Interesting! I don’t think this answers the question of “why not hermaphrodites” though. A hermaphrodite can produce two different types of gametes, large and small (I assume this is what trees do).
Yes, but the distinction between gametes had to evolve first from asexual, i.e., undifferentiated reproduction, while hermaphroditism requires some added complexities, as it has to combine both sexes in a way that works. And as long as divided sexes work well enough, there isn’t much selection pressure to go that route.
As for why this is more common in plants, I’m intuitively guessing that there are a bunch of issues involved that I’m not familiar with either. But a major driver is probably that (land) plants are sessile and tend to require some space for themselves. The problem for plants with differentiated sexes is then that if their nearest neighbours happen to be of the same sex, the chance of their spores reaching those of the opposite sex is drastically lower than for hermaphodites, as the latter have potential partners in every neighbour.
This wouldn’t generally be an issue in mobile animals, who have to find and approach their mates anyway.
This wouldn’t generally be an issue in mobile animals, who have to find and approach their mates anyway.
Unless they’re slow and uncommon as snails, in which case the cost of looking for a new mate might be high enough that developing hermaphroditeness was worth it.
Interesting! I don’t think this answers the question of “why not hermaphrodites” though. A hermaphrodite can produce two different types of gametes, large and small (I assume this is what trees do).
Yes, but the distinction between gametes had to evolve first from asexual, i.e., undifferentiated reproduction, while hermaphroditism requires some added complexities, as it has to combine both sexes in a way that works. And as long as divided sexes work well enough, there isn’t much selection pressure to go that route.
As for why this is more common in plants, I’m intuitively guessing that there are a bunch of issues involved that I’m not familiar with either. But a major driver is probably that (land) plants are sessile and tend to require some space for themselves. The problem for plants with differentiated sexes is then that if their nearest neighbours happen to be of the same sex, the chance of their spores reaching those of the opposite sex is drastically lower than for hermaphodites, as the latter have potential partners in every neighbour.
This wouldn’t generally be an issue in mobile animals, who have to find and approach their mates anyway.
Unless they’re slow and uncommon as snails, in which case the cost of looking for a new mate might be high enough that developing hermaphroditeness was worth it.