The Elements of Evolution (43-14-5) Pollution Adaptation

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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.