Adaptation
Adaptive evolution affects all species. ~ American evolutionary geneticist David Gresham
Repeated evolution can occur by reusing the same genetic mechanisms over and over again. ~ American evolutionary biologist Erica Bree Rosenblum
Evolution is commonly adaptive to environmental circumstance. Adaptation is initiative in reaction – a positive process for survival.
Adaptive radiation – the rapid evolution of ecological and phenotypic diversity within a clade – accounts for much of life’s diversity. ~ American evolutionary biologists Christopher Martin & Peter Wainwright
The evolutionary process is really fluid. ~ American paleoanthropologist Richard Potts
Organisms evolve for an array of reasons: to better exploit resources, to improve breeding odds, to optimize efficiency, or to overcome an onslaught otherwise from predation or poison. The desire to live drives evolution.
Biological evolution is an economic process in which the entities of life – all organizational units from genes to species – change through time according to the circumstances in which they live and which they helped to create. It is a process governed by opportunities, challenges, and limitations. Feedbacks between life and its environment effect evolution. ~ Geerat Vermeij
Perception
Biological information processing should seek to maximize performance subject to constraints on information processing capacity. ~ American cognitive scientist Chris Sims
Perception is the fundamental mechanism of the mind to function in the world. The process begins with sensation: the collation of sensory stimuli. Perception starts by turning sensations into symbolic representations. These symbols are then identified using memory and categorization: generalizing specific symbols into classes via hierarchical pattern-matching. The hierarchy of classification is based upon priority of utility: which categories are most useful, based upon knowledge which may be inborn or learned.
Perception concludes by deriving the meaning of the identified symbols, especially with regard to affinity or avoidance. What to eat, and what not to get eaten by, are illustrative.
Learning involves reprioritizing and creating new categorizations, as well as modifying and creating new linkages between concepts, which are essentially codified categories.
Learning applies to the conceptual constructs derived from perception which evolve into “purer” abstractions that are only remotely related to actuality – sometimes so distantly so that the connection is obscured. Learning is the evolution of a mind.
The greatest risk of perception is misidentification: to mistake what is for what is not and vice versa. Confusion is commonly generated during the generalization stage, while categorizing.
Perceptual generalization in any efficient communication system will necessarily follow an exponential function of the cost of perceptual error. ~ Chris Sims
The information channels of sensation are limited by type and quality. Certain organisms can see, but not very well. They compensate by having a keener sense of chemistry (e.g., olfaction), touch, or audition. Many sensations are a confluence of sensory inputs.
Altogether, adaptation drives at perception capabilities which best suit the environment in which an organism lives, with the minimal overall sensory distortion that permits workable perceptual acuity.
Sensory systems adapt to suit the lifestyle or environmental niche of an animal through discrete molecular and biophysical modifications. ~ David Julius et al
Sensory adaptation is reflected in static and dynamic characteristics of sensory performance. Viewed statically, sensory systems are highly selective: their sensitivity varies across stimuli as if they favor certain stimuli over others. Dynamically, stimulus selectivity varies across time; it is modified when the environment changes. ~ American vision scientist Sergei Gepshtein
Regarding sensation, the parameters of evolution are constrained by physics, biochemistry, economies of biological production, and fitness within the phyla (body plan). That withstanding, to think just in terms of physical senses under-scopes the issue of perceptual adaptation.
The mind compensates for deficiencies in sensation via a variety of heuristics, including reliance on knowledge as a basis for probabilistic assessment. Sensation and perception both involve learning, most markedly during early development.
Whereas biological structures and behaviors are all that may be observed, the real work of perception is done in the mind, and so is as much a focus for adaptation as biomechanics.
Sea Snakes
Sea snakes are found in warm coastal waters from the Indian Ocean to the Pacific. Many species inhabit coral reefs. All sea snakes have paddle-like tails which aid propulsion.
While venomous, having a long body means that their tail might be mistaken for food by a hungry fish when only that portion can be seen, such as when a snake is moving through a cluttered reef. To compensate, some sea snakes evolved light sensors in their tails. This gives them some sense of exposure as to how visible their tails may be.
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For the littlest ones, evolution is a matter of self-selection. Microbes carve their own evolutionary path: deciding how to adapt themselves to environmental conditions via self-induced genetic modifications. Horizontal gene transfer often facilitates the process.
For macrobes, adaptation often appears via bodily change (phenotypically). But physical changes may be the tip of the iceberg to functional transformations, including behaviors.
Predation has long been recognized as a key ecological factor for adaptive responses in morphology, behavior, and alterations in life-history variables. But predation risk also drives the evolution of social complexity. Under threat of predation groups become more cohesive. Organisms stay together to minimize risk. Proximity evolves social interaction regimes. If membership in a group becomes a precondition for survival, predation adaptively affects mating and breeding regimes as well as everyday life.
The significance of predation for the evolution of social complexity can be well illustrated by behavioral and morphological adaptations of highly social animals showing division of labor, such as eusocial insects and cooperatively breeding fishes. Predation risk has the greatest explanatory power of social complexity. ~ Dutch evolutionary biologist Frank Groenewoud
Adaptation ultimately involves alterations in the genetic fabric. But adaptation is not necessarily confined to being within an organism. Solutions may involve environmental transformations (envirotype). Organisms and their ecology are entangled.
Organisms are constructed in development, not simply “programmed” to develop by genes. Living things do not evolve to fit into preexisting environments, but co-construct and coevolve with their environments, in the process changing the structure of ecosystems. ~ Kevin Laland et al
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Evolution plays an important role in range spread. ~ American environmental biologist Christopher Weiss-Lehman
Dispersal and speciation have long been considered interrelated, yet range extension of a population has long been thought merely a matter of demographic metrics, such as dispersal inclinations and rates of birth and mortality. Extending the range of a population commonly involves adaptive evolution when habitat conditions differ from those where the core of the population live. Environmental pressures at a population’s edges stimulate adaptation which may eventuate into speciation.
Tropical Rainforest Spiders
Preferring lives of solitude, spiders rarely live in groups. But if conditions warrant, spiders do what it takes.
In the mountain highlands of Ecuador, cobweb spider families stay together to help each other raise offspring.
Though not especially hospitable, highland conditions are milder than in the tropical rainforests which lie below. There, strong rains and powerful ant predators make life for solitary spiders untenable. Even small groups are easily overwhelmed. So, cobweb spiders in the rainforest form large colonies. A single colony may comprise tens of thousands of spiders which cover an entire tree canopy in a giant web: the power of cooperation.
The spiders make dense webs that require a lot of silk. When the webs get damaged by strong rains or colonies are attacked by predators, some spiders can protect their offspring while others go and make the repairs. ~ Ecuadoran evolutionary biologist Leticia Avilés
Ecuadoran spiders are not the only ones to come together when living otherwise is unwise. Social living among spiders has arisen independently many times.
(Not) Freezing
Physiological processes require liquid water. Freezing the water inside cells spells certain death unless you happen to be a well-fed Panagrolaimus davidi worm, in which case you just feel a bit stiff.
Despite the peril of being on the icy edge of death, many organisms live at temperatures below the equilibrium freezing point of their body fluids. To do so necessitates specific adaptations which vary among species, though many antifreeze solutions involve protein agents: those wily macromolecules who know how to keep the plumbing working.
The precise physiological challenge of not freezing differs between marine and terrestrial environments. Life in the sea is more thermally stable than on land, owing to the much greater specific heat capacity of water compared to air. If it’s cold in the water, it’s likely to stay that way for some time. Thermal shocks are a greater hazard on land.
Life evolved in the sea, so most organisms have a body fluid similar to seawater in osmotic strength. Hence, for most marine organisms, freezing is a relative problem: if the sea remains fluid, so do they.
Teleosts arose during the Triassic. These ray-finned fish make up 96% of all living fish, with abundant diversity: 26,840 extant species. Teleost’s great advantage is their jaws, which may protrude from their mouths, enabling them to grab prey and draw it in.
Teleosts are unusual in having thin blood: roughly half the osmotic strength of seawater. This dilute blood likely reflects an early evolutionary phase in fresh water, when thinner blood would have reduced osmoregulatory costs. It means that teleosts in polar waters are living with blood that would easily freeze without some serious compensatory devices.
Polar teleosts avoid freezing via a suite of anatomical, physiological, and chemical adaptations. One of them is an antifreeze protein (AFP). P. davidi also avoid catching a lethal cold via an AFP.
AFPs inhibit ice crystal formation and are effective in minute concentrations. Antifreeze proteins bind to specific faces of growing ice nuclei, preventing them from reaching sufficient size to achieve thermodynamic stability, and thereby inoculate bulk freezing. The proteins thermally assess cold spots and so can efficiently prevent freezing.
Icefish (notothenioids) live off the coast of Antarctica. They evolved AFPs once, when first adapting to the freezing waters, with a genetic recipe that is uniquely efficient in manufacturing antifreeze proteins. These fish also have aglomerular kidneys which prevent losing AFPs in their urine.
Representing a major evolutionary radiation, icefish are the dominant teleost on the continental shelf of Antarctica. Later-evolved notothenioids which live in warmer waters to the north of Antarctica have the AFP-generation gene, but do not express it, as the protection is superfluous.
Antarctic fish are ever in frigid waters, and therefore need antifreeze throughout their lives. In contrast, many fish on the fringes of the Artic basin only face freezing in winter. Many of these fish synthesize their AFPs seasonally.
Arctic fish employ a different AFP than Antarctic ones, with exception. Codfish created on their own AFP, selfsame as icefish, illustrating convergent evolution for not freezing to death in frigid waters.
The thermal environment on land is more volatile than in the sea, and the evolutionary responses have been correspondingly complex. Some land animals employ antifreeze proteins. Certain insects, frogs, turtles, and at least 1 snake can tolerate extracellular water freezing. Water in the cells remains fluid, and metabolism continues, albeit at a low level. A minority of these creatures actually induce extracellular freezing via ice-nucleating proteins as a form of virtual hibernation. Meantime, AFPs are employed within cells to prevent recrystallization, averting tissue damage from ice crystals growing while the animal is frozen.
Some insect protein antifreezes have been found to be many times more effective than fish AFPs. Such efficacy is needed to survive the wider range and rapidity of frigidity to which these insects are subjected.
Many arthropods exposed to extreme cold also produce various cryoprotectants sufficient to significantly drop the freezing point of their cells. Some species employ just 1 compound, while others use a complex chemical suite which both protects and minimizes cellular injury. Especially prominent in damage control is the use of trehalose, a double-glucose sugar which helps maintain membrane integrity during desiccation (anhydrobiosis).
Cellular dehydration is a significant problem for organisms whose extracellular fluids freeze, as the increased osmolarity of the residual unfrozen water is high, pulling water from the cell. Many unicellular beings residing in super-salty homesteads or able to hold up under drought are often incidentally able to withstand freezing. Maintaining cell membrane integrity plays a resounding role in such resistance. There appear to be significant physiological parallels and evolutionary convergences between drought and freezing tolerances, involving stress (chaperone) proteins and similar osmolytes (compounds affecting osmosis).
Whereas land animals are motile and may migrate to locales that lessen environmental stresses, plants are sessile, and must withstand whatever challenges the weather delivers. Using a variety of ice-nucleating agents, plants typically initiate freezing in xylem and extracellular fluids as a way to raise the odds of cell survival. Besides the potential insulating effect of an ice shell, extracellular freezing withdraws water from cells. So, fighting freezing to death involves similar responses to dealing with drought.
Besides their extensive precocious knowledge, plants learn the best ways to survive water shortages. For many plants, aridity is a common problem, whereas life-threatening cold is less frequent. Being able to apply honed skills to an infrequent hazard improves the probability that a plant can manage to survive.
Islands
Isolation plays games. ~ Richard Potts
Adaptation is always ecological, and opportunistic toward probable survival. Life-history variables shift with envirotype.
Islands spark accelerated evolution. ~ American scientist Lisa Gross
Islands represent unique challenges to both plants and animals. Evolutionary responses have been various, with some underlying consistencies. Once such constant is that island species evolve faster than mainland species, especially during the early generations, which are finding their best fit to island isolation.
Islands have produced both radiation and a strong degree of convergent evolution. ~ English paleontologists Adrian Lister & Peter Rawson
Animals
Living large can become advantageous for an island-bound animal. Predators drop away as prey gain girth.
As we have already seen, island birds repeatedly supersized. Not being able to fly away became increasingly insignificant as predatory attack became more remote.
Already-large monitor lizards turned into Komodo dragons on Indonesian islands. But then, today’s Komodo dragons are a serious step down from earlier, extinct Australian relatives.
Conversely, shrinking to reduce nutrient requirements is an equally viable strategy. While rats on the island of Flores grew to a meter to establish dominance, elephants shrank to the size of large hogs on the 2 separate occasions they made their way to Flores. A hominid isolated on Flores became a pygmy, as did humans that arrived there within the past 50,000 years.
Flores the only example in the world where insular dwarfism has arisen twice in hominins. ~ American evolutionary biologist Joshua Akey
Settling in on Madagascar, cockroaches grew to 6 cm or more and started hissing to scare off potential troublemakers. Meanwhile, hippos on Madagascar became pygmies. This was not the only instance of hippos shrinking. Finding their way to Cyprus, hippos dwindled to the size of sea lions.
Timing matters. A rattlesnake that made its way to an island in Baja California grew into a giant. The rattlesnakes that followed got a case of adaptive intimidation: shrinking rather than face well-established stiff competition.
Islands often inspire animals to try something different. Small ones enlarge while big ones shrink. Whereas rodents tend to gigantism, carnivores, artiodactyls (even-toed ungulates), and rabbits deign to dwarf.
Food resources and the ability to self-limit population size determine the evolutionary vector on an island. In the interest of self-preservation, rodents can prudently control their population numbers in absence of predators; but hippos, deer, and other artiodactyls cannot. Early island generations may at first upsize from the new-found abundance, then be forced to shrink as food becomes scarcer.
Lizards typically dine on various animal fare. The Balkan green lizards that inhabit islands in the Greek archipelago found meat running scarce, so they are adapting to eating greens: their digestive tracts are lengthening, and they are developing pouches (cecal valves) to harbor gut microbes that feast on floral food. Such changes are common in herbivorous reptiles, as in the green iguana.
Plants
Several plant traits are known to evolve in predictable ways on islands. ~ New Zealander biologists Patrick Kavanagh & Kevin Burns
Islands present new challenges to plants. Evolutionary responses have been consistent.
To better establish themselves where real estate is severely limited, herbaceous species on islands often become woody. Larger leaves are another predictable trend, to make the most of land allotment and try to crowd out competition.
Island plants also produce larger seeds. This reduces dispersibility, which is an advantage when seeds spread afar may be lost at sea. Further, larger seeds tend to generate larger seedlings, which are more likely to grow and outcompete punier neighbors. Coconuts innovated to create gigantic seeds which can survive sea voyages and then establish themselves on new islands.
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Not all ‘islands’ need to be surrounded by water. Climatic changes can lead to the constriction or dissection of terrestrial environments producing isolated, spatially restricted refuges. Refuges can produce the same geographic isolation of organisms as islands. ~ Catherine Forster
The New World callitrichid monkeys, which include tamarins and marmosets, are phyletic midgets. Arid conditions during the Neogene and early Quaternary periods likely reduced and isolated forest regions into small refugia, limiting resources and adaptively pushing callitrichids toward dwarfism.
The remarkable diversity of birds in Amazonia may have transpired similarly. The zones of high avian radiation were concentrated in areas over 100 meters in elevation. In the Neogene and early Quaternary periods, sea level rises from marine transgressions may have divided the Amazon basin into numerous islands and archipelagoes, engendering allopatric (isolation) speciation and diversification of bird faunas within each refuge.
Ocean basins and lakes may also become isolated, affecting biotic evolution in an island-like manner. The 3 genetically distinct groups of cichlids in Lake Tanganyika likely arose during the Pleistocene, when the water level dropped, and the lake split into 3.
The explosive radiations of animals during the early Cambrian may be explained by island-like isolations. The supercontinent Rodinia was fragmenting during that time, creating additional continental shelves and coastline areas which facilitated biotic evolution.
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Facilitated variation via ecology is one way modification leads to speciation. A change in environment provokes envirotypic adaptation.
Gall Plumbing
Many insects form conspicuous galls on their host plants. The galls provide the inducer insects with an isolated and exclusive habitat, constant and high-quality food supply, physical barrier against predators and parasites, and mitigated environmental stresses such as desiccation and temperature fluctuation. The gall-forming insects manipulate the plant growth and morphogenesis for their own sake in a sophisticated manner, thereby inducing elaborate plant structures as “extended phenotypes” of the insects. ~ Japanese biologist Mayako Kutsukake et al
Rather than build their own nests, social aphids induce galls on a plant to secure a comfortable home. Some gall nests have an open structure, with waxy walls. Other aphids prefer sealed structures, where they live for months without emerging.
Aphids feed exclusively on plant sap. As gall tissue provides a constant sap supply, no foraging outside is needed. But there is a plumbing problem: wastes must be flushed. Some galls have small openings through which soldier nymphs dispose colony refuse.
This is a compromise. Completely closed colonies offer the coziest abode: safe from all but gall-boring predators.
Aphids in closed galls engineered a clever solution: inducing galls with an inner surface specialized for absorbing water. Honeydew waste is promptly removed via the plant vascular system. This innovation evolved independently in different aphid species. The engineering skill is hereditary.
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Evolutionary conflict can drive rapid adaptive evolution, sometimes called an arms race, because each party needs to respond continually to the adaptations of the other. Evidence for such arms races can be seen in morphology, in behavior, or in the genes underlying sexual interactions or host-pathogen interactions. ~ American evolutionary biologist Katherine Geist
Resource allocation trade-off has influenced the evolutionary diversification of weapons, revealing a rich interplay between developmental trade-offs and both pre- and post-mating mechanisms of sexual competition. ~ Australian evolutionary biologist Leigh Simmons & American zoologist Douglas Emlen
Evolutionary arms races often occur. A typical example are male animals that produce ever-spectacular weapons to fight off rivals and secure a mate. Antlers and tusks are exemplary.
3 preconditions appear necessary for adaptive arms races to reach extremities. 1st, there must be competition for a limited resource, typically access to reproductive females. 2nd, the resource must be confined in a way that its access is largely defensible by an animal. 3rd, males fight one-on-one for the right of access. Where guerilla tactics may succeed does not lead to the evolution of extreme bioweapons.
Backdoor Beetles
Male coastal dung beetles develop extravagant weaponry in the form of horns or enlarged mandibles. They employ these armaments during combat over females, protecting the entrance to tunnels where the lady of the household resides. The horniest male beetle almost always triumphs.
At some point, the biological cost of built-in armory becomes too expensive. So it is with the coastal dung beetle. Their horns may make up 30% of body weight.
Because nutrients are shifted to horn growth, males with stunning racks may have stunted eye growth and tiny testicles. The cost is so high for coastal dung beetles that only a relative few males have competitive horns.
An adaptive alternative arose: cheat. Some male coastal dung beetles stay relatively small and grow no horns. Instead, they are vested with terrific testes that produce extraordinary amounts of sperm.
Sans fighting weapons, these nimble dung beetles dig backdoor tunnels, where they charm the female within while the brute at the den entrance is none the wiser. Ninja lovers do not mate as many females as the larger beetles, but they make the most of every opportunity.
For male coastal dung beetles, there are 2 ways to have the equipment where it counts.
Feathers & Fur
Animal furs generally have at least 2 kinds of hair: guard hair (longer, straighter, colored) and ground hair (shorter, denser, and often curly).
A similar distinction exists for bird feathers. Bird wings are optimized for flight, but they also serve as insulation, among other things.
Mammal hair varies from straight to curly. For aquatic mammals, hair shape allows an air layer to be maintained within the fur during submersion, increasing water repellency.
After being soaked, many animals shake themselves to rid their bodies of water. They do so at optimal frequencies. The bigger an animal gets, the slower it shakes. Whereas a mouse shimmies at 27 hertz – back and forth 27 times per second – a bear shakes at 4 hertz. Loose skin helps by oscillating to release more water than if skin were tighter.
Shedding water efficiently is important. It could otherwise cost 25% of daily caloric intake in maintaining body temperature, and risk hypothermia and death.
For land mammals, fur features are optimized for the thermal habitat. That often means keeping out the cold.
Polar bear fur is only 5 cm thick yet impenetrable enough to keep bear bodies warm, even when temperatures reach a frigid –40 °C.
In adapting to the Arctic climate, polar bears got stinky feet. Pungent paws leave scent tracks by which polar bears can find one another; because sheer white-on-white in a vast wilderness would be a surefire formula for species extinction.
It is commonly assumed that feathers and fur keep animals warm by trapping a layer of air that slows thermal conduction. Instead, radiation shielding often plays a larger role.
Bird feathers are often barbed, with long appendages that diffuse thermal radiation. Barbed feathers and the individual hairs of fur are precisely arranged to repeatedly backscatter infrared light. These create a radiative shield that provides thermal insulation.
If trapping heat were the point, polar bears would be black. Instead, their white fur maximizes reflectivity. This keeps polar bears warm, as it creates the most effective radiative shield.
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It is extremely common that animals are cryptically colored, thereby blending in with their surroundings. If hypothesized natural selection via random mutation were at work, such optimization would not be so ubiquitous. In that case, poorly colored animals would regularly appear. Instead, such ill-adapted mutations are quite rare: typi-cally, symptomatic of general developmental deficiencies
Eyelashes are found on a wide variety of mammals. They are always about 1/3rd as long as the eye is wide. This allometric proportion is the ideal length for diverting airflow around the eye, and thereby minimizing evaporation.
Poison Avoidance
We lose baits all the time. ~ American entomologist Grzegorz Buczkowski
Cockroaches first appeared during the Carboniferous, over 320 MYA. These were the ancestors to modern roaches and mantises. The cockroaches scurrying about today debuted during the early Cretaceous, 140 MYA.
In response to assault of toxic baits by people, who consider their home not a proper residence for roaches, German cockroaches rapidly adapted. The sugar glucose, put in baits to attract, instead took on a bitter taste, which the roaches avoided.
Instead of taste buds, cockroaches have taste hairs on many parts of their body. The taste mechanism is much the same: the vibrations of sensed molecules trigger signals deciphered for substance quality.
Glucose is a come-hither sweet to countless life forms, and a ubiquitous biological fuel. Given poisonous glucose, roaches learned that glucose out of context to a natural sugar is a trap. This adaptation took less than a decade from the time glucose baits were introduced. The exact evolutionary mechanism remains a mystery.
Mosquitos are another highly unpopular pest. They quickly evolved not to linger on walls that have been treated with insecticide. Instead, untreated ceilings are preferred.
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The outcome of adaptation is not necessarily a physical change in an organism. It may instead be innate intelligence, such as adjusting reproduction according to environmental conditions.
Pig Litters
Female wild pigs adjust their litters based upon resource availability. When food is scarce, mothers birth about 5 piglets, all the same size. The little ones fight it out for the most productive teats. Not all thrive. Survival becomes a matter of spirit.
When times are less lean, a mother instead produces a litter with piglets of various sizes. This limits sibling rivalry. The bigger piggies get the choice teats, while the little ones get by on teats that give less milk. All have a better shot at survival.
Epigenetics
As life evolves, the adaptive tricks of the past are stored genetically. This toolkit provides the means for variations and new combinations.
Tiny tweaks can work wonders. A single gene regulates the complex wing patterns, structures, and colors for mimicry in butterflies. Epigenetic controls are applied to achieve the desired result.
A great number of traits are managed by expression of gene complexes which are often regulated by environmental conditions, and even by state of mind.
Animal development is rife with thresholds. The expression of complex morphological and behavioral phenotypes may be sensitive to many environmental or circumstantial stimuli at multiple periods during development. ~ American biologist Mark Rowland & Douglas Emlen
The caste that eusocial ants and bees have for life are epigenetically determined from the same set of genes, based upon their diet early on. The size and shape of dung beetle horns are sensitive to nutritional history.
The vast array of coloration that animals display varies via regulation of a sparse set of genes. In some species, colors, and other visible features signal social status.
Lusty Birds
The tiny red-backed fairy-wren, averaging 8 grams, is endemic to the rivers and coastal areas of Australia. Sexual dimorphism comes with coloration. Females and juveniles are a drab brown.
Males are either drab or wear a fiery red collar, depending on how hot their sex life is. Hormones regulate which path a male fairy-wren is on, based upon social interactions prior to the breeding season.
A male feeling empowered by success in flirting develops into a bright guy, flush with testosterone. Conversely, those who get negative social feedback – receiving scant interest from females or picked upon by other males – dulls a bird as testosterone drops. While the drab males do breed, the reds sire more offspring that year.
The plumage change is not permanent. In a year or 2, a fairy-wren male may be better placed to put on a bright red collar and go further in fathering.
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Such status badges as fairy-wrens wear are found in numerous social animals, most prolifically birds. Relative success in sociality regulates hormones which reversibly alter genetic expression.
Male house sparrows have black bibs which distinguish dominant birds from subordinates by size. Harris’ sparrows with the blackest head feathers are the top birds.
Male African red-shouldered widowbirds wear epaulets. Territory holders have larger and redder shoulder patches than those that float between territories.
Whether a male orangutan is flanged or not is a simple hormonal change, activated by the ape’s recognition of social circumstance.
The above examples illustrate how easily, and dynamically, phenotypic changes can be accomplished in animals via psychology.
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Some adaptations appear as invention: a creative saltational step well beyond what has done before. Sometimes these leaps are keepers, as defining a lineage. Other times, evolution produces a singular novelty.
Planthopper Leap Gear
Mechanisms previously thought only to be used in manmade machines have evolved in Nature. ~ English zoologists Malcolm Burrows & Gregory Sutton
Gears rarely appear in Nature. The only known life with a working gear is the planthopper: a phloem-sucking plant pest common across the globe, only a bit bigger than a flea.
Planthoppers are camouflaged to look like their meal ticket. To avoid attention, they walk on branches extremely slowly. In case one is spotted, an adult can leap within milliseconds with a force of 500 Gs: flea-like indeed. A human would pass out at such a speed. Other insects simply can’t keep up.
To powerfully jump in an instant, both legs need to move precisely synchronously: otherwise a leap begets an out-of-control spiral.
Nymphs are not as able leapers as adults, so they have an assist: legs in gear. Juvenile planthoppers have a set of matching gears between their legs that coordinates takeoff. Each gear strip has 10–12 teeth, with each tooth 350–400 micrometers long.
Other insects, such as grasshoppers, push their legs straight up to hop. Planthoppers propel themselves with a breaststroke motion: their legs a mirror of each other in splaying out to the sides.
This precise synchronisation would be impossible to achieve through a nervous system, as neural impulses would take far too long for the extraordinarily tight coordination required. ~ Malcolm Burrows
Close registration between the gears ensures that both hind legs move at the identical angular velocity, propelling the body without yaw rotation. The gears are asymmetrical, so that they can only rotate in the direction needed to leap.
Planthopper gear teeth have rounded corners at the point where they mesh: a feature human engineers use for shock absorption, to prevent gear teeth from breaking off.
A nymph might recover from a broken gear tooth in a regenerative stage, but an adult would be doomed if it relied on the same mechanism and had to jump. After molting a half-dozen times, the gears are lost at the final ecdysis into adulthood. Nevertheless, with stronger leg muscles, adults are better jumpers than juveniles.
Owing to a mathematical oddity there are a limitless number of ways to design intermeshing gears. Planthoppers evolved an ideal set for their intended purpose.
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Planthoppers are not alone in having mechanical joints that seem more machined than biological. A flightless weevil endemic to Papua (Trigonopterus oblongus) has a nut-and-screw joint connecting its legs to its hips, 0.5 mm in size. (All other known hip-leg joints are either ball-and-socket (as in humans), hinges, or saddle joints.) The unique mechanism allows the weevil to tuck its legs below its body.
Adaptation may arise from opportunity, most notably new nutrient sources. At other times, the habitat demands change if a population is to survive. Such envirotypic demands include ecological associations: whether from parasites, predators, prey, or from one’s own kind: sociality. Group dynamics within a population may itself propel adaptations.
Harvester Ants
Collective behavior arising from interactions among societal members can determine a population’s success.
Common in the southwest United States, red harvester ants reside in the desert. Their water intake comes mostly from metabolizing the fats in the seeds they eat.
Each harvester ant colony is founded by a single queen. 5 years into her reign colony population may stabilize at 10,000. Offspring colonies are founded by newly mated gynes: females destined by caste to become queens.
A colony’s foraging activity varies daily, depending upon local food supply and weather. Foragers interact, creating a feedback loop of communication that results in a community decision as to a day’s level of effort.
Ants lose water when foraging. Sometimes it can be so hot and dry that a foraging ant can desiccate to death.
The more successful colonies forage when conditions permit, forgoing foraging on scorching days. Restraint does not compromise a colony’s prospects of survival over its queen’s 25-year lifespan. Colonies that selectively fail to forage do as well as those that brave the hot sands.
Foraging theory for social insects generally presumes that the more food collected, the better for reproductive success. Harvester ants show that this is not necessarily so.
Harvester ant colonies store seeds for many months. Conserving water in various ways is a ubiquitous adaptation for desert animals, as red harvester ants demonstrate by intelligently managing their activity to optimize outcomes.
A daughter harvester ant founds her new colony far from her birthplace. There is no communication between mother and daughter colonies. No cultural transmission occurs. Yet the daughter knows what her mother did and how it fared. The tendency to forgo foraging is passed from queen to gyne epigenetically: a precious precocious knowledge. (Molecules coating DNA can’t literally impart information. The use of epigenetics here is loose: referring to molecular artifacts that signify a mind-energy complex.) Thus, each colony takes its innate cue for best foraging practices from former founders.
Rapid Adaptation
Evolution is always moving quickly but we tend not to see it because we typically measure it over longer time periods. ~ English evolutionary biologist Greger Larson
The pace of evolution can be accelerated by need, and can even occur within a single generation. Adaptation is specific, directed to the prospect of improved fitness.
Evolutionary change can occur rapidly. ~ American evolutionary biologist Yoel Stuart et al
Viruses know that their hosts are always working to keep them out or kill them if they get in, so viruses are constantly tuning their genic toolkits. How they do so often follow patterns. Vaccine makers have discovered how to anticipate the variants that influenza viruses use. This discovery relies upon the fact that viruses typically take the savviest path.
Seasonal influenza virus undergoes rapid evolution to escape human immune response. ~ geneticist Natalja Strelkowa & German physicist Michael Lässig
Such optimality in evolution has been seen in HIV. HIV populations readily discover every possible mutation and select those that best accelerate viral replication.
HIV quickly acquires genetic mutations that allow it to escape the immune system and multiply in the body. HIV establishes a chronic infection despite heavy immune predation. ~ German evolutionary microbiologist Richard Neher et al
Plants also adapt rapidly. The Pyrenean rocket is a small flowering plant native to the mountains of southern Europe. It somehow made its way to the lowlands of Belgium in the 1st half of the 19th century. Within 20 generations of its landing in Belgium, the rocket had adapted to a quite different biome.
Rapid adaptation to a novel environment can increase population growth rates, which also promotes spread. ~ American entomologist Marianna Szücs et al
Polar Bears
400 TYA, polar bears diverged from brown bears in fewer than 20,500 generations. The most significant adaptation was to the cardiovascular system, so that polar bears could tolerate the extremely fatty diet of eating blubbery seals: the only catchable meal.
Polar bears also adapted to the frigid temperatures of the Arctic Circle where they live, moving about on ice and snow, and swimming in near-freezing water.
Sticklebacks
Repeated evolution can occur by ‘reusing’ the same genetic mechanisms over and over again. ~ American evolutionary biologist Erica Bree
The stickleback is a family of small fish that has long been abundant in the oceans. 10,000 years ago, as the last ice age relented in glacial melt, most of the 16 species wound up in new freshwater streams and lakes.
Around the world, sticklebacks, well-adapted to life at sea, faced a freshwater dilemma: evolve or die. Within 10 generations they all underwent similar changes: swapping their armored plates and defensive spines for a lighter freshwater form, as well as adapting from saltwater conditions to fresh. This convergent evolution happened thousands of times.
Most of the rapid adaptations were not genetic mutations. Instead, epigenetic regulation altered the activities of genes.
Sticklebacks are an excellent example of how rapidly adaptation can happen, convergent to functional needs.
Coywolves
The environmental pressures presented by humans has forced animals into desperation. Wolves have been hard put from deforestation and deliberate persecution by man.
Within the past few decades, a scarcity of sex partners led wolves to mate with coyotes and dogs. If they survive at all, such interbreeding usually leads to offspring less robust than either parent. The coywolf combination is an exception.
Coywolf DNA is mostly coyote, with 25% wolf and 10% dog (mostly large breeds, such as Doberman Pinschers and German Shepherds). The result: remarkable adaptation.
Coyotes disdain hunting in forests. Wolves prefer it. Interbreeding has produced an animal skilled at predation in both open terrain and densely wooded areas.
At 25 kg or more, many coywolves have twice the heft of coyotes. With larger jaws, more muscle, and faster legs, coywolves can take down small deer solo. A pack can even kill a moose.
Since the 21st century dawned, coywolves’ range has come to encompass America’s entire northeast, urban areas included. They are continuing to expand in the southeast, following coywolves’ arrival there half a century ago.
This is astonishing. Coyotes never managed to establish themselves east of the prairies. Wolves were killed off in eastern forests long ago. But coywolves have been able to spread into a vast and otherwise uninhabitable territory.
Indeed, coywolves are now living even in large cities, including Boston, New York, and Washington. This adaptability to urban life owes to greater tolerance of people and noise. Wolves dislike humans.
Interbreeding helped urbanization by broadening the animals’ diet. Versatile tastes prove handy for city living.
Coywolves consume pumpkins, watermelons, and other garden produce as well as discarded food. They snack on rodents and other smallish mammals.
Parks and lawns are usually kept clear of thick underbrush, so catching squirrels and pets is easy. Cats are commonly eaten skull and all.
Thanks to this bounty, an urban coywolf needs only half of the territory it would require residing in the countryside. Getting into town is easy: railways provide corridors that make the trip easy.
Surviving in the city requires keeping a low profile. Coywolves have adjusted by becoming nocturnal. They have also learned to watch out for cars, looking both ways before crossing a road.
Even coywolf cries blend those of their ancestors. The 1st part of a howl has a deep pitch like that of a wolf, but this then turns into a higher-pitched, coyote-like yipping.
Coywolves illustrate that species is a contrived concept. Evolution is not the simple branching that textbooks might lead one to believe.
But then, humans also illustrate such hybridization, in modern Europeans carrying Neanderthal genes, and east Asians have Denisovans in their DNA. Whereas plants are judicious, animals breed with what they can.
Tibetans
Tibet is one of the most hostile places that people inhabit. The weather is bitterly cold. The air is thin and dry.
But locals do well. First arriving 12,500 years ago, humans adapted to Tibetan conditions within 150 generations by introgression of Denisovan DNA suited to the habitat.
Admixture with other hominin species has provided genetic variation that helped humans to adapt to new environments. ~ American evolutionary biologist Emilia Sánchez et al
Florida Lizards
The degree and quickness with which they evolved was surprising. ~ Yoel Stuart
The green anole is a smallish arboreal lizard common in the southeastern United States and some Caribbean islands.
Though not a chameleon, the green anole can change color: from various brown hues to bright green. The ability to change colors is common to anoles, which are iguanas.
The brown anole is a cousin to the green, native to Cuba and the Bahamas. It has a highly invasive species, helped along by humans who kept them as pets and carelessly let them into the domain of the green anole, who cannot compete against the brown anole.
Within 15 years and 20 generations, green anoles in south Florida adapted to invasion of the browns by growing larger sticky toe pads, allowing them perch higher up the branches of trees where they and their hatchlings are safer.
Big-headed Ants
It’s scary that it can happen so quickly. ~ American entomologist Andrew Suarez
Big-headed ants are named after their soldiers, which are larger than other workers and have outsized heads. These ants are aggressively invasive.
The environment influences how large big-headed ant soldiers become. If they face fierce competition from local ants, soldiers grow even larger heads, with commensurately prodigious mandibles that are their weaponry.
Big-headed ants are not the only combative ant that adjusts its size to suit its habitat. Fire ants begin morphing their body size within 60 days to meet environmental demands.
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Animals are most adaptive during early development. Tadpole tolerance to insecticides is most successful when exposure occurs during the embryonic stage.
Polluted Fish
Beginning in 1947, practicing business-as-usual, General Electric plants dumped massive quantities of PCBs and other toxic pollutants from their new factories into the Hudson River. The pollution nearly wiped out all of the river’s young Atlantic tomcod, which are river-bottom dwellers.
50 years later, researchers discover that 99% of the remaining Hudson tomcod now have a genetic mutation that prevents these pollutants from killing them. That adaptation appears in only 10% of tomcod in cleaner waters. Fish forced to survive in filth tuck the pollutants into their fat cells. That means that striped bass that eat tomcod ingest a heavy dose of stockpiled toxins. This moves the necessity for toxic adaptation up the food chain.
Similarly, PCB pollution in Massachusetts New Bedford harbor nearly killed off the killifish there. Like the Hudson tomcod, specific genetic mutations allowed the genetic transcription factor that gets gummed by PCB to work again, even though the PCB pollutants still bind to the factor proteins.
Even though the specific molecular changes found in PCB-resistant tomcod and killifish are different, in both species the same major gene is responsible for the resistance. ~ American toxicologist Mark Hahn
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Fish are not the only ones that have rapidly adapted to poisoned water.
Polluted People
The Atacama Desert is a 1,000 km long plateau on the Pacific coast of South America, situated west of the Andes Mountains. Scant rain falls there. Some spots haven’t got a drop in recorded history.
But people came to the Atacama and stayed. The Atacameños fished the Pacific, hunted game, and herded livestock in the highlands. And were poisoned by drinking the water there.
The Atacama Desert sits on top of arsenic-rich volcanic rock. The concentration of arsenic in Atacama drinking water runs to 20 times the level considered safe for human consumption.
While many Atacameños succumbed to arsenic poisoning, some survived, thanks to a protective mutation that detoxifies arsenic in the liver. This genetic variation spread throughout the population within a few thousand years.
Peppered Moths
This is one of the most iconic examples of evolution. ~ English zoologist Martin Stevens
Before the industrialization of England, the peppered moth was sprinkled to match light-colored lichen-covered tree bark. By the early 20th century, the peppered moth developed black wings, so that it was invisible when it settled on soot-covered tree trunks. Regulation that improved air quality resulted in peppered moths becoming peppered again.
A jumpy transposon is responsible for the moth’s rapid adaptation. Evolutionary biologists have no physiological explanation for how pulses of environmental change are able to effect this fast and accurate transformation in ecological mimicry.
Mosquitofish
There is a high mortality rate among Bahamian mosquitofish when predators are abundant. In such circumstances, males become desperate to mate: rejecting elaborate courting rituals for more frequent and sometimes forceful encounters.
Habitat fragmentation by humans – building roads that isolate waters – changed the situation for some mosquitofish populations. There are fewer predators about.
Within 12 generations of living in a safer environment, male mosquitofish genitalia adapted and courtship again became par for the course.
Birds
Dinosaurs and their descendants diversified through several bursts of niche-filling radiations. Evolution is not necessarily the gradual process that Darwin imagined.
On his trip to the Galápagos Islands, Darwin was puzzled by the diversity of finches there: a smorgasbord of variation.
Within the past million years finches had arrived on those dry volcanic islands, blown far from where they intended. Since then, the descendants of immigrant finches evolved into 18 separate species, falling into 3 groups, ranging in size from less than 10 grams to more than 40. The 3 groupings are ground finches, tree finches, and the warbler finch.
Besides size, the most conspicuous difference in body shape is the beak, which relates to diet. Finches with short, thick beaks feed on seed, which would be too tough to crack with the slender beaks of insect feeders. The warbler finch, and other finches with long bills, probe flowers for nectar, or the holes in wood for tasty critters.
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In 1981, a young, male, large cactus finch immigrated 100 km from the Galápagos island of Espanola to the small island of Daphne Major. The immigration is remarkable for its extreme distance. Clearly this bird willed its way on a unique adventure.
Unable to return home to mate, the sturdy immigrant bred with a female medium ground finch on Daphne Major, who liked the male’s body, beak, and song.
One of the 1st generation of offspring bred with another medium ground finch, but all other offspring inbred. From generation 2 onwards, the lineage behaved as an independent species. Generations 4–6 came from a single brother-sister mating in generation 3. Despite close inbreeding, the lineage was highly fit, judging by their reproductive output and high survival.
Fledgling finches imprint on the features of their parents. When later choosing a mate, females discriminate on the basis of bill size and shape, as well as song and body size. Hence, this new species was immediately reproductively isolated.
The new species, dubbed big bird, is 1 of 4 different finches that live on Daphne Major. Beak morphology was a key factor in this new finch’s success. Unlike medium ground finches, big bird finches can efficiently exploit the large woody fruits available in dry seasons.
Hybrid speciation of the big bird lineage exemplifies the potential evolutionary importance of rare and chance events. Expansion of the population from 2 individuals to 3 dozen was conditioned on the founder being a male with a distinctive song, and facilitated by the chance occurrence of strong selection against large bill size in a competitor species, the medium ground finch. ~ American evolutionary biologist Peter Grant
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On Daphne Major, medium ground finches competed with large ground finches for seeds. Both had big beaks. Then came a drought in 2004–2005 that diminished seed supply. The medium-sized finches lost ground to their bigger cousins as many died of starvation. Medium ground finches quickly adapted by having offspring with smaller beaks, giving them greater feeding flexibility in seed size.
Besides the beak, Galápagos finches have developed specialized feeding habits. Woodpecker and mangrove finches use various tools to pry arthropods from crevices. Twigs, cactus spines, and leaf stems are popular tools of the trade.
Vampire finches peck at the base of booby feathers and suck booby blood. The boobies try to dislodge them, but the little feathered vampire finches still manage to steal their bloody meals. These finches also shove and kick seabird eggs against rocks to crack them, widen the cracks, then suck out the contents.
Life on the Galápagos is tough. Food is often difficult to come by.
As a group Darwin’s finches rip open rotting cactus pads, strip the bark off dead branches, kick over stones, probe flowers, rolled leaves, and cavities in trees, and search for arthropods on the exposed rocks of the shoreline at low tide. They consume nectar, pollen, leaves, buds, a host of arthropods, and seeds and fruits of various sizes. ~ Peter Grant
Potato Whiteflies
The sweet potato whitefly acquired a new bacterium from the genus Rickettsia. As a result, infected whiteflies develop faster, are more likely to survive to adulthood, and lay more eggs, especially more female eggs.
The bacterium induces a higher percentage of daughters because the bacterium is genetically transferred only by females. In less than a decade, the population count of whiteflies with Rickettsia went from 1% to 95%. Biological success proliferates, no matter how it is arrived at.
Hawaiian Crickets
If you’re a male cricket, your life is defined by calling. How are you going to find a female, and once you do, how are you going to get her to mate with you without your call? ~ American evolutionary zoologist Marlene Zuk
Male crickets usually sing to attract a mate. Cricket singing is done by rubbing wings. The evolutionary changes described pertain to alterations in wing design.
The crickets on Hawaii discovered that their marital crooning made them easy targets for parasitic flies. The flies deposit their maggots on the crickets. The maggots burrow into the cricket and eat it alive.
Within a few generations of the parasites becoming a plague male crickets evolved to stay silent. Shortly thereafter they regained their voice: a cat-like purr at a lower register than the parasitic flies could hear. Understanding female crickets mated with quiet males until they could get their singing act back and have adjusted to the new register. These cricket adaptations recurred independently on the different islands of Hawaii – an instance of convergent evolution.
Purring crickets communicate with potential mates. ~ American evolutionary behavioralist Ann Hedrick
Coral
The rising temperature of the world’s oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. ~ American biological oceanographer Mark Eakin et al
Coral comprises a colony of marine invertebrates, individually called a polyp. Each polyp is a spineless animal, only a few centimeters in length, with a set of tentacles surrounding its mouth.
An exoskeleton of calcium carbonate is excreted near the base of coral. Over the years this builds into extensive reefs.
Coral reefs are the rainforests of the sea, forming some of the most diverse ecosystems on Earth. Though occupying less than 0.1% of the world’s ocean surface, coral reefs are home to 25% of all marine species. Coral is one of the most important keystone species on the planet.
Rising acidity and warming water present extreme challenges to coral. Their demise leaves a reef bleached of its color and an ecosystem in terminal distress.
To a degree, coral can adapt, and do so quickly via epigenetic changes. In less than 2 years, high-growth warmwater coral can tolerate greater heat stress. This involves management consultants. Coral acclimatize to the heat by hiring temperature-tolerant algal symbionts.
Acclimatization can allow corals to acquire substantial high-temperature resistance quickly. ~ American marine biologist Stephen Palumbi et al
Germ Plasm
Germ plasm liberates constraints on somatic development. ~ American biologist Andrew Johnson et al
Germline cells are the special cells of sexual reproduction. In contrast, the bodily cells of a multicellular eukaryote are somatic.
Passed from one generation to the next, germline cells are immortal. Conversely, somatic cells can live only as long as the organism in which they are produced.
Early in animal development a small number of embryonic cells produce primordial germ cells (PGCs). These develop into sperm or eggs. All other cells develop as the soma.
There are 2 ways to produce a PGC: epigenesis or preformation. In epigenesis, PGCs are induced from pluripotent cells via extracellular signals.
In preformation, material in the egg – germ plasm – is inherited directly by a few cells in the embryo. The germ plasm instructs these cells to become PGCs.
Germ plasm functions to segregate PGCs from somatic cells at the inception of development. This relaxes genetic constraints on the mechanisms that govern early somatic development. ~ Andrew Johnson
Some invertebrates, including roundworms and vinegar flies, employ germ plasm for germline cell differentiation. Preformation also repeatedly evolved in certain vertebrates, including frogs and teleosts.
This convergent evolution had a singular purpose: to enhance evolvability. Clades that practice preformation can speciate much more rapidly than those that rely upon epigenesis.
Animals can evolve more rapidly with germ plasm. ~ Andrew Johnson
Epigenesis is a conserved process. Mammals produce PGCs via epigenesis. That is because enhanced evolvability via preformation has a price. Germ plasm leads to an evolutionary dead end.
Salamander-like amphibians, lacking germ plasm, evolved into reptiles, which begat birds and mammals.
Epigenesis is open-ended phenotypically. Preformation is not. Frogs with germ plasm can only evolve into other frogs – many different frogs, but still just frogs.
Coevolution
Interactions between species are as diverse as they are pervasive. The result is a continual process of adaptation and counteradaptation, where each species evolves continually to keep abreast of interacting species. ~ American evolutionary biologists Sarah Otto & Scott Nuismer
All organisms live in a web of relationships, from synergistic to antagonistic. Interdependencies evolve that range from mutualistic to parasitic.
Species can coevolve with more than one other species. Legumes have simultaneously evolved sophisticated coevolutionary relationships with their rhizobia and with their pollinators. Many parasites evolve adaptations to multiple hosts by partitioning their interactions into different life history stages. ~ John Thompson
Coevolution is adaptive intertwining among species that is inspired by their interaction. Biological self-interest drives the gyre of coevolution.
Coevolutionary arms races are a powerful force driving evolution, adaptation, and diversification. They can generate phenotypic polymorphisms that render it harder for a coevolving parasite or predator to exploit any one individual of a given species. ~ South African zoologist Claire Spottiswoode & Martin Stevens
African cuckoo finches lay their eggs into the nests of tawny-flanked prinias. Female prinias try to weed the fakes out. This can be perplexing, as parasitic eggs are strikingly selfsame. Egged on by parasitism, prinias epigenetically develop new shell hues to catch the cuckoos out. The cuckoo finches retaliate with new fakes. This adaptive cycling takes place within a few breeding seasons. Evolution moves at requisite pace.
Milkweed
Pyrrolizidine alkaloids (PAs) are produced by angiosperms as a defense against insect herbivores. More than 660 PAs have been identified in over 6,000 plants. PA production capability independently evolved many times.
Milkweeds are one plant genus which adopted PAs as a toxin of choice to ward off predation. (Milkweeds also produce cardenolides to thwart insects. Cardenolides are steroids which stop the hearts of the little pests that dare prey upon milkweeds.) There are over 140 distinct milkweeds.
The problem that certain milkweeds encountered with PAs is that some predators adapted to the toxin. Danaine (milkweed) butterflies lay their eggs on milkweeds. When the eggs hatch, the larvae feed on the milkweeds, concentrating PA in their bodies to make themselves inedible to birds that would otherwise pick them off.
Pyrrolizidine alkaloids are an ineffective defense against milkweed butterflies. Furthermore, they are actually beneficial to them since they take in these chemicals for their own defense against their predators. ~ American botanist TaTYAna Livshultz
Recognizing that there is no good reason to waste energy producing poisons that don’t work, at least 4 different milkweeds gave up making PAs.
Fruit
Most woody tropical angiosperms produce fleshy fruits and rely on animals for seed dispersal. Fleshy fruits have evolved independently in more than half of extant angiosperm families. ~ Israeli evolutionary ecologist Omer Nevo et al
Fruit is a wily confection of plants: an ovary enclosing seeds, often full of sweet and succulent pulp, exquisitely designed to appeal to specific consumers. The seeds are hardened to survive the rigors of the animal digestive tract. The plan behind fruit is for an animal to eat it and deposit the seeds some distance away from the fruit-bearing plant; the deposit conveniently including some fertilizer.
The colors of fruits are optimized to contrast with the natural background according with the visual system of the intended seed disperser. The size, shape, form, smell, and taste of the fruit conforms with what primary seed dispensers like. Even the location of fruit and its presentation on the branch cater to the intended audience.
The simians in Uganda are trichromats (tricolor vision). The birds there have even better vision. By contrast, most lemurs in Madagascar are dichromats: red-green color-blind, only seeing yellow-blue light. Compensation for lemurs comes in a keen sense of smell.
Ugandan fruit eaten by the birds and simians there contrast with foliage in the red-green spectrum. In Madagascar, fruit for lemurs pops in yellow-blue contrasts. Further, the fruit smells right.
In plants that specialize on seed dispersal by lemurs – an olfactorily-oriented primate – fruits increase scent production and change their chemical composition significantly more than sympatric species whose seeds are largely dispersed by birds. Lemurs use these shifts in fruit scent to identify ripe fruits. ~ Omer Nevo et al
Balanites wilsoniana decided it liked elephants. This African tree produces a pungent odor detectable for kilometers. Elephants gobble up the large fallen fruit, not minding at all if it is a bit fermented. Only elephants can swallow the fruits and defecate the sizable seeds whole. This plant’s seeds won’t even germinate unless it passes through an elephant’s gut.
The traveler’s palm is not a true palm: instead, belonging in the genus of bird-of-paradise plants native to southern Africa. Bird-of-paradise plants produce red or yellow seeds easily detected by their avian consumers. In Madagascar, where traveler’s palms reside, the seeds are a brilliant blue: a color appreciated by aye-ayes, a lemur with ultraviolet sight.
Knowing that their fruit is intended to be eaten, many plants add a laxative to their seeds, easing their offsprings’ passage.
Fruit sweetly illustrates that plants somehow know what should be unknowable, and that an intelligent force is behind evolution.
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Coevolution between parasites and their hosts is an endless war. Viruses are the most confrontational provocateur of evolution.
Marine Cyanophages
These parasites impose a tight control over the composition of marine microbial communities. ~ French virologists Frédéric Partensky & Laurence Garczarek
There are typically 100 billion viral particles per liter of water in the top 50 meters of most marine ecosystems. Marine viruses outnumber bacteria 10 to 1.
A cyanophage is a virus that infects cyanobacteria. The impact that cyanophages have on victim populations differs. They exert the strongest predation pressure on the most abundant bacteria. Scarcer species are much less affected. Thus, through their culling, viruses help maintain bacterial diversity.
Different strains of the same bacteria have genomic variances that create ranges of susceptibility or resistance to viruses. Hence, only a fraction of a population is killed when attacked by a cyanophage horde.
Several cyanobacterial genes are found in viral genomes. Most often these are employed in energy metabolism, such as photosynthesis.
The viruses themselves may optimize the functioning of these genes. During infection, viruses hijack the translational machinery of their hosts and make the bacteria express the viral version of the genes. This strategy helps maintain host metabolism long enough for the viral replication cycle to be completed.
These viral optimizations may then be picked up by other viruses, and by their bacterial targets. This gyral dynamic drives evolution for both. For cyanobacteria, what doesn’t kill you might make you and your offspring stronger.
Parasitic Plants
Microbes are not the only ones who practice horizontal gene transfer as an intelligence exercise and self-determine their own evolution. Parasitic plants monitor their hosts and selectively pilfer genes. They also themselves evolve genes which mimic their hosts. This diligence pays off in maintaining the ability to evade host defenses and improve nutrient extraction as needed.
Red Queen Hypothesis
Now, here, you see, it takes all the running you can do, to keep in the same place. ~ the Red Queen in Lewis Carroll’s novel Through the Looking-Glass (1871), explaining to Alice in Wonderland why she is exhausted from running, yet finds herself still under the tree where she started
In 1973, American evolutionary biologists Leigh Van Valen and Michael Rosenzweig independently concluded that organisms must constantly adapt to merely survive. Van Valen termed his hypothesis “Red Queen”; Rosenzweig called it a “Rat Race.” In the annals of popular science, Van Valen won, thanks to the charming literary allusion.
In Van Valen’s view of Nature, species continually evolve, but their fitness never increases because each adaptation is countered by adaptations by their competitors and enemies.
~ English evolutionary biologist Michael Brockhurst
Animal studies have shown statistically constant extinction rates between competing species that coevolve. From this, Van Valen proposed the Red Queen hypothesis to explain his hypothesized law of constant extinction: that the probability of population extinction remains constant.
Leigh Van Valen formulated the law of constant extinction after attempting to show that the probability of extinction increases with taxon age and finding instead that it does not. ~ Finnish evolutionary biologist Indre Zliobaite et al
Other evolutionary biologists have invoked the Red Queen hypothesis to explain the advantage of sexual reproduction, in offering variability and faster adaptive response compared to more economical and efficient asexual reproduction. The Red Queen hypothesis has also been applied to host-parasite coevolution, and to explain aging as evolutionarily advantageous.
From the time a species originates to its demise, its evolutionary success may be measured in several ways, such as the extent of its geographical range. Such metrics often form a bell curve, with a rise toward a central peak, followed by a decline to extinction. This pattern has been repeatedly observed. 2 primary drivers are involved: biotic competition and abiotic environmental factors.
Evolutionary innovation is influenced by intrinsic factors – the less-predictable origin of the ‘right’ variants at the right time, able to exploit either existing or new resources. ~ American paleobiologist Charles Marshall
Neither competition nor environmental change correlates well with the rates at which species arise. But, once expansion starts, the rate at which genera reach their peak in the fossil record strongly correlates with biotic competition intensity. The rise of large mammals was suppressed by dominant dinosaurs, for instance.
The probability of when a genus might reach its evolutionary peak is not related to how long it has been around. But, for large mammal herbivores at least, demise violates the law of constant extinction: the probability of extinction rises over time. (One known exception: the North American mammalian fossil record from the Cenozoic era fits the law of constant extinction with remarkable fidelity.)
Biotic drivers of evolution pertain mainly to the peak of taxon expansion, whereas abiotic drivers mainly apply to taxon extinction. At the end of its history, when a taxon is already rare, its final extinction is more likely to be a consequence of environmental change. In this light, the law of constant extinction might be usefully reformulated as the law of constant peaking. ~ Indre Zliobaite et al
The population dynamics behind evolutionary peaking and extinction resemble a gyre obeying self-organized criticality.
Mutualism
As every multicellular eukaryote carries an extensive microbiomic society, coevolution is a constant within all plants and animals. Microbes often invoke evolution in their hosts, as exemplified by the potato whitefly and Rickettsia bacteria.
Deep-Sea Battery
Deep-sea vents are suffused with chemical energy, including hydrogen (H2), hydrogen sulfide (H2S), methane (CH4), and oxygen (O2), courtesy of carousing reactions with oceanic crustal rocks. This comes about because billions of years of photosynthetic activity has created a thin veneer of highly oxidized material over a mass of chemically reduced rock. Earth is essentially a battery.
Hydrothermal circulation taps this battery: fluids circulating through seafloor crust are charged with reduced (electron-laden) compounds, emerging as jets into the oxidizing environment of the ocean. The carry of compounds from the reduced rock mass (the anode) to the ocean (the cathode) is a flow of electrons. As with any battery, this electron flow is a usable energy source.
Mussels evolutionarily managed the neat trick of harboring bacteria in their gills that convert these charged ingredients into metabolic sustenance for the mollusks. Some of the mussel microbes specialize in methane, others hydrogen sulfide, while some like their energy straight with a chaser: H2 and O2.
A hydrogen-consuming symbiosis is particularly surprising. Hydrogen consumption by life forms is rare, as its natural production in reliable quantities occurs in only a relatively few places, such as in vent systems hosted by peridotite (mantle-like) rock. In being highly reactive, hydrogen is a uniquely rich energy source.
Pathogen Protection
Symbiosis for nutritional purposes is ubiquitous. Pathogen protection is less well-known.
In unique antennal glands, female beewolf digger wasps cultivate symbiotic Streptomyces bacteria. The wasps secrete the bacteria into their larval brood cells. The larvae uptake the bacteria. When the larvae spin their cocoon, the bacteria are placed outside, where they act as protection against a wide range of potentially detrimental microbes, doing their job by producing a cocktail of at least 9 different antibiotics.
Wood cockroaches nest in the crevices of decaying tree trunks. These same crevices are home to fungi that parasitize cockroaches. The microbiome inside wood cockroaches evolved a solution: internal manufacture of an antifungal. The cockroaches insulate their homes from infestation by plastering it with their feces, which keeps the fungus at bay.
What works for a family scales up. Termites are colonial descendants of cockroaches. The earliest termites created an antifungal paste which they applied to their nests.
In evolutionary time, termites and their microbes cultivated a more mutualistic perspective with regard to fungi. Now, only a quarter of the termite species chew wood with the help of digestive microbes. The other 75% maintain fungal gardens upon which they feed.
Codependence
Over time, mutualism may become codependence, or it may develop into an even more intimate relation: union. Endosymbiosis is the intracellular capture of former symbionts.
Biological merger has repeatedly occurred, in seemingly creative ways. The mitochondrion, chloroplast, and nucleus of eukaryotic cells have double membranes: an apparent vestige of evolutionary union of an eocyte and bacteria.
Eocytes are anaerobic thermophiles that thrive in a sulfur-rich marine environ. Eocytes are archaea, with an evolutionary lineage distinct from bacteria.
These prokaryotic cousins – archaea and bacteria – have repeatedly teamed up. Purple sulfur bacteria and eocytes are naturally complementary endosymbiotic partners, as the metabolic needs of one are met by the metabolic waste products the other. An endosymbiotic relationship has flourished between a purple bacterial host and an eocyte symbiont, based on hydrogen and sulfur recycling, with CO2 taken in.
The selective integration of cellular life was merely a matter of time given coherence in evolution. Much later plants and animals coevolved symbiotically. The waste product of plants – oxygen – became a ready fuel of animal respiration, as well as plants themselves being nourishment.
The coevolution of flowering plants and pollinating animals is well-known. To attract pollinators and seed dispersal agents, plants evolved advertisements of various sorts: distinctive visual patterns and colors that contrast with their background, unique scents, and morphological features. Plants place their flowers and fruits on long peduncles (stalks), facilitating detection and approach. Even leaves may act as billboards.
Over time, a relationship between a plant and pollinator may even become exclusive: the animal and plant coevolving to a private mutualism.
Darwin noted the Malagasy star orchid, with a nectary at the base of a corolla tube 25 cm deep. While he knew of no pollinator, Darwin predicted one existed, one with a tongue long enough to reach the nectar. Years later, a local giant hawk moth was discovered, named Morgan’s sphinx moth, with a 30-cm tongue, longer than its body. In a pattern of coevolution, star orchids and hawk moths have developed such that certain hawk moths are suited to pollinate specific star orchids.
In the cloud forests of the Ecuadorian Andes mountains live nectar bats. Many varieties of these bats have tongues that reach 3.9 cm. One, Anoura fistulata, has a tongue that can extend to 8.5 cm: 150% of its body length, comparable only in tongue length to a chameleon. When not in use, the bat stores its tongue in a special tube in its thorax. With it, in an exclusive relationship, the nectar bat can dine on the flowering Centropogon nigricans, which stores its nectar at a depth only the tongue of A. fistulata can reach.
The Cuban tropical vine Marcgravia evenia has a unique disk-shaped leaf. For nectar bats foraging by echolocation, the leaf produces an echo signature which can be clearly differentiated from the echoes produced by background foliage. This reduces bat search time by half in finding the vine they were looking for.
The Cuban tropical vine’s echolocation trick is especially impressive when considering that different bat species have different echolocation techniques. Somehow the Cuban tropical vine knew exactly who its customers were and catered to them.
Cave-dwelling bats, such as fruit bats, make quick echolocation clicks by popping the tongue from the floor of the mouth to the roof. Bats that feed upon flying insects have a different clicking action: one that lasts 5 times that of the quick pop of cave bats. The longer signal is better for detecting flying prey than for navigating obstacles.
Plants & Animals
Plants are in a unique position in Nature: largely self-sufficient autotrophs, consciously knowledgeable about their relationships with other species, and able to concoct chemical persuasions for those interactions. Conversely, as heterotrophs, animals are dependent on interactions with other species of macroorganisms to survive. Compared to plants animals are clueless.
The power of plants in their manipulative intelligence is met by the ability of animals to destroy. While plants create ecosystems, all that most animals do is ransack their habitats for sustenance and defense. Constructive keystone species that build without destruction, such as coral, are relatively rare exceptions.
Plants typically provide the biological substrate for symbiotic relationships. Mutually beneficial relations between a plant and an animal often involves other characters with less than benign intent. Acacia trees illustrate.
Acacia & Ants
Bullthorn acacia trees in Central America produce large, swollen thorns at the base of their leaves. Acacia ants are stinging, wasp-like ants that hollow out the thorns and use them as nests.
The bullthorn caters to the ant’s nutritional needs: providing a sugary nectar for adults, and a high-protein liquid for growing larvae. The ants reciprocate by defending the tree.
A climbing vine will be met by vigorous chewing of its tendrils by the ants, defeating its advance. A competing plant near the acacia is dealt with similarly: its leaves nipped off by ant bites, hence hastening the plant’s demise.
The protective ants are alerted to nearby landing of any leaf-grazing insects by vibration. Their stings and bites persuade an intruder to graze elsewhere.
Vigilance is not the only benefit that bullthorns get from acacia ants. The ants’ microbiome includes bacteria that synthesize antifungal compounds.
The ants very presence on the trees keeps parasitic fungal growth in check. Thus, the ants act as an immune system agent for the bullthorn.
Beltian Body Snatcher
At least one spider doesn’t swear by silk to get fed. The acacia jumping spider is largely vegetarian.
The acacia spider has an especial fondness for Beltian bodies: nutritiously rich nubs that form at the leaf tips of an acacia tree. The Beltian bodies are intended as payoff for acacia ants, which the tree feeds in return for protection from herbivores that are more of threat to them than the jumping spider.
The spiders live out on the tips of old leaves, where ants seldom go. To feed, they head in to newer leaves. The ants diligently defend their Beltian body food supply, so a filching spider has to be stealthy and swift.
A spider waits for an opening, then darts in. It clips off a Beltian body, holding the morsel in its mouth as it makes its getaway. Once back on an undefended part of the plant, the sneaky spider enjoys its booty.
Acacia spiders have keen eyesight, are especially fast and agile, and likely possess considerable cognitive skill. Stealing from a colony of ants right under their noses is one snappy trick.
The interdependence between ants and acacias allowed for the emergence of the Beltian body. Now the only known case of spider herbivory depends on this interdependence. ~ American biologist Christopher Meehan
Adaptive Predatory Cycle
A primary driver of adaptation comes from avoiding being eaten, and, conversely, getting enough to eat. Predator and prey competitively cycle through evolutionary time.
Plants are proficient in concocting metabolites for all sorts of purposes. Many of these metabolites are chemical concoctions that make them distasteful to potential predators, or otherwise inhibit their consumption.
Herbivores adapt to ingest poisonous plants. Some then adopt the toxin for their own protection. That poison may be passed on to predators who adapt to tolerate the toxin.
Bad Taste
Brightly colored pitohuis are endemic to New Guinea. These birds take advantage of another animal’s culinary taste to keep themselves safe.
Flashy pitohuis are an advertisement of aposematism (warning coloration). These omnivorous birds are toxic.
Pitohuis are fond of melyrids: small beetles stuffed with batrachotoxins, which are unique steroidal alkaloids more poisonous than strychnine. This is much the same toxic brew found in poison frogs.
Like pitohuis, poison frogs of the Amazon forest are outrageously colored, in a variety of patterns, depending on locality. Poison frog subspecies stew their own variety of toxin. 28 different poison frog alkaloids are known.
Frog-eating snakes learn to recognize the pattern of local dart frogs but will peck at those that don’t match the local coloration pattern; local being 10 km or less. A snake risks death in swallowing one of these frogs if the snake is not adaptively tolerant to the specific toxin.
The poisons in the birds and frogs are hand-me-downs from their diet. The ultimate source of the toxin is not known but is most likely the ultimate food-chain producer: plants.
This predator-prey dynamic of locality in aposematism accounts for the wide variety of warning patterns in a single-prey species. Localized patterning such as this have been observed in butterflies, bees, and other animals. Pitohui and poison frogs are exemplary of innumerable animals that mark themselves and their eggs as inedible.
Marked Against Predation
Chemical defense in an evolutionary cycle is common. How it works as a deterrent is not obvious. If every predator had to eat colorful prey to learn an unappetizing lesson, it’s inscrutable how conspicuous colors have the chance to evolve as a defensive strategy. The answer is reputation.
Learning by observing others occurs throughout the animal kingdom. Species ranging from fruit flies to trout can learn about food using social transmission. ~ English zoologist Rose Thorogood
Birds and other animals often see conspecifics take a bite of something. If the reaction to taste is one of disgust, an observer learns to avoid the experience. Such knowledge may be communicated to others as the occasion arises.
The animal world abounds with brilliant colors and striking patterns that either disguise or attract attention. They are all the product of an adaptive strategy to survive predation or increase the chance of propagation. Damselfish exemplify deceptive coloration designed to thwart predators.
False Eyespots
The Ambon damselfish is a frequent prey to larger fish. The young are naturally more vulnerable. Clever adaptation has given damselfish fry a better chance of reaching adulthood.
Ambon damsels are a pale yellow, with a distinctive circular black eye toward the top of their tailfin, which fades as a fish matures. Ambon eyes can quickly change during juvenile development. When fry are in a hostile environment, their false dorsal fin eye grows larger, while the display of their real eye shrinks.
The false eye gives a predator a 1st impression that the damselfish is headed in the opposite direction of where it is actually going. This misdirection gives the Ambon 5 times better odds of survival than damselfish which lack the eyespot.
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Many lepidopterans (moths and butterflies) have coloration patterns that act as camouflage. As insectivorous birds have caught on to the ruse, adaptation has furthered the camouflage cycle.
Quite a few lepidopterans have false eyespots that mimic birds of prey that prey upon the small birds that prey upon them. These spots are often displayed with behaviors that startle a predator into thinking that the tables have been turned on it.
Birds are not the only worry for butterflies. Lepidopterans may be laid low by small jumping spiders which can leap on their heads and deliver venom that instantly paralyzes.
The red-banded hairstreak is a butterfly endemic to the southeastern United States. If feeds on fallen tree leaves which are frequently crawling with spiders.
Besides the striping that begat its name, the hairstreak has a pattern on its hind wings that looks like its head. On the ground in the presence of spiders, the hairstreak constantly moves its hind wings to elevate the effect of its false head being real. Spiders are suitably seduced: jumping at the false head, thereby saving the hairstreak from a bad hair day.
The spiders get frustrated with futile attacks. They learn not to bother with prey that they cannot capture. This enhances the efficacy of the hairstreak’s false head.
