The Ecology of Humans (15-15) Lookout from the Dung

 Lookout from the Dung

Pilobolus is a fungus that starts its life cycle as a black sporangium let loose in the grass. A grazing herbivore eats the fungal bit.

The sporangium survives digestion intact, emerging in excrement. Once back out in the open air, embedded in fertilizer, the spores in the sporangium germinate, growing as a mycelium on the dung.

The fungus then fruits to produce more spores. The sporangiophore – asexual fruiting structure – is a transparent stalk (hypha) which rises above the excrement, ending in a balloon-like globe. A single sporangium forms on top.

Sporangiophore stalks like this are common in simple fungi. Pin mold on stale bread employs the same technique.

In Pilobolus, the globe (subsporangial vesicle) acts as a lens, focusing the light onto a carotene light receptor. If not properly focused, the fungus adjusts its hypha to point it at the light.

Pilobolus anticipates the human eye: a focusing element that acts as a lens, a photoreceptor that acts as a retina, and the means to detect unacceptable reception and adjust accordingly.

Pilobolus employs its eye for more than aiming its spores. The vesicle swells until it bursts, shot-gunning spores at up to 50 km per hour.

One tiny nematode appreciates the physics of this. The nematode slips into the sporangium. When the capsule bursts, ejecting the spores, the nematode rides along, traveling much farther than it otherwise could.