Pilobolus is a fungal genus whose fruiting bodies consist of a stalk ending in a spore mass that is launched via turgor pressure to disperse the spores. The fruiting bodies grow towards light, which ultimately influences the direction in which the spores are launched.

It seems that gravity-directed growth would be sufficient to ensure an upward trajectory, so I'm wondering what the value is of phototropism. Has this been studied at all?

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    $\begingroup$ Most of the "why" questions have no scientific answers. Reasonable questions I can imagine in this context would be: "how does it work?" (pathways involved), "how did it evolve?" (evolutionary history of individual components of the system and of the system as a whole) and "what kind of biological role does it play?" (if we knock out some key components of the phototropic system: would it break/diminish spore dispersion?). $\endgroup$ – har-wradim Apr 8 '15 at 16:05
  • $\begingroup$ @har-wradim I'm most interested in the third question - i.e. what adaptive benefit does the phototropism confer? $\endgroup$ – augurar Apr 9 '15 at 5:30
  • $\begingroup$ My thoughts - pilobolus is only 1 cm tall. Its spores need to be ingested by an animal to complete its life cycle. Suppose some detritus like a dead leaf landed on or near it. If it only responded to gravity, the spore mass would be ejected into the leaf and back onto the dung on which it grew, and will not likely be eaten until the dung is thoroughly decomposed and the area re-grown with vegetation for host animal to feed upon (herbivores give a wide berth to feces when feeding). By growing toward the light, the spore mass misses the dead leaf and travels over a meter away, onto vegetation th $\endgroup$ – H Preston Brown Feb 15 '16 at 22:14

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