Neotrogla is a genus of barklice noted for its reversed sex roles and organs, traits shared by all species of the genus.
Female Neotrogla possess a penis-like organ, properly termed a " gynosome ", but interchangeably called a penis. They aggressively seek out mates, while males are more selective. During mating, the female mounts the male and penetrates his small genital opening from behind.
However, the evolutionary origin of the penis-like organ remains a complete mystery. “Usually, a new structure evolves as a modification of a previously existing structure,” Yoshizawa explained. Such an adaptation would be “exceptionally difficult” because of the need for male and female genital structures to change at the same time.
My question is: OK, it’s “exceptionally difficult”, but what are the possibilities?
The only thing I can think of is that at some point it didn’t use any sex organs at all, similar to creatures who mate via external fertilization (I’m not sure if this works on land) and then evolved into a penetration system. But I don’t know if that’s a viable hypothesis.
I must be missing something, because this seems nonsensical to me. Of course a penetrative and a penetrated sex organ can evolve, as they did for all the other animals that have them. Why does it seem so implausible that they would have evolved with, opposite sexes from what we expect.
Also, by what means are they defining male and female? Maybe they don’t match up well with our concepts of the sexes.
“Also, by what means are they defining male and female?” Males have sperm and females have eggs.
Which is still the case here. I studied Seahorses in college and while the males get “pregnant” and nurture their offspring, males fertilize females in a fairly normal way, unlike what is happening here.
I think the problem is looking at the end product of evolution and not being able to dream up the intermediate forms. I think it’s safe to say this change didn’t happen overnight, and the fact that the female gets nourishment during the act is probably a major factor in why it evolved the way it did.
These Barklice live in an extremely hostile environment so to survive, the females had to come up with a way to reproduce while getting life-sustaining nourishment at the same time. Over a long period of time, females evolved a method for doing that so that it now works perfectly every time. How this evolved is currently unknown, but it doesn’t strike me as any more unexpected than male Seahorses giving birth.
Presumably the issue is that the neotrogla are just one branch of a tree that indicate that the common ancestor had sex organs that wouldn’t be a good starting point for such an evolution. That is also a good candidate for explaining why they’d find it implausible that they would evolved with “opposite sexes”, the common ancestor already had sexes the way round we expect.
OR
The editors of this entry could have found a particularly unimaginative and inexpert biologist to question on the topic.
No one has a problem if these develop “from scratch”. The problem is if the neotrogla evolved from some creature which had the more common alignment and needed to switch over. It’s hard to see how that could be done, even in incremental steps.
And if they did develop from scratch, then that would presumably mean that the neotrogla would have to have split off before the development of sex organs in other creatures.
There are many other species which have arrangements that differ widely from the male-penis-female-vagina system, but in those cases it’s not hard to see how they might have arisen incrementally from a MPFV arrangement. In the case of the neotrogla it’s much harder, as it would seem to require simulataneous and fundamental changes in both males and females.
That’s the issue, anyway, as I understand it. Not saying there’s no way around it, of course. Just curious as to what that might be.