An interesting article in The Scientist, on Amazon mollies.

I think you need to subscribe to the site, before you can view it, but here's the link anyway: http://www.the-scien.../display/55611/

Basically, amazon mollies (Poecilia formosa) are a parthonogenic species. The species consist entirely of females, which are pretty much genetic copies of the mothers. Although they don't incorporate male genetic material into their eggs, female amazon mollies do need to mate with males of other species (either the sailfin mollie, P. latipinna, or the shortfin mollie, P. Mexicana) before their eggs will develop into baby female fish. Amazon mollies are thought to have resulted from a long ago cross of the two species.

What scientists don't understand is why all three species don't go extinct. Theoretically, the ever increasing proportion of females should use up all the available males, preventing them from mating with females of their own species, causing a population crash.

This doesn't happen. The researchers theorize there are several reasons why. First, the Amazon species and the two species may occupy different habitats, and only come in contact periodically. Second, males are thought to be able to distinguish between females of their own and a P. formosa, and preferentially mate with their own species. (In support of that hypothesis, I think I remember a study claiming that the males only mate with P. formosa females in an effort to increase their marketability with females of their own species--inciting piscine jealousy, in fact.)

The scientists do note that in spite of these potential safegaurds, populations do periodically go extinct at a local level. But since the ranges of P. latipina and P. mexicana extend far beyond that of the range of P. formosa, there are reservoirs of males to extend into the range of P. formosa and make up for the lost males of their own species.

I'm confused. If they're reproducing via parthenogenesis then why do they need sperm?
Why would parthenogenesis evolve if you still need a male? It seems that having all of your species being able to reproduce but still being reliant upon a male would be a serious problem.

Andrew, you gotta take Vertebrate Reproduction this fall... Many parthenogenic species need some kind of "male" stimulation either to produce viable eggs at all like Amazon mollies, or to produce more like some species of whiptail lizard. The all-female whiptails take turns acting as "males", mounting each other as a fake copulation. This seems to stimulate the mounted female, who is at a hormonal peak of more estrogen in her ovulation cycle, to produce more eggs; the mounting female is at a low estrogen point in her cycle. The mollies seem to need a mating behavior, and physical contact, to stimulate the transformation of viable oocytes into developing embryos; it's a matter of signal transduction to stimulate the hypophysis-pituitary-gonadal axis (in a million words or less). It sounds like a song title waiting to happen, but an animal may need a social interaction to trigger a hormonal cascade; "Stimulate Me".

I think I'll have time for it next fall--I'll see. Oh what will my mother say when she hears I'm taking a course in sex? She'll really think I'm a liberal hippie then.

My confusion stems from the article saying a sperm from a related species' is required.

....To initiate embryogenesis, however, Amazon mollies require sperm from the males of one of two closely related, but sexually reproducing, species sharing their habitats in southern Texas and northern Mexico -- the sailfin molly (Poecilia latipinna) or the shortfin molly (Poecilia mexicana)....

Does anyone know if the sperm is actually binding with an egg or is it the stimulation that does the deed? Perhaps the article has misquoted someone?

Finding a female when all of your comrades are female is easy, but if you still need a male---what's the advantage? I would assume higher reproductive output, but there has to be a bottleneck since a male is still required.

Does anyone know if the sperm is actually binding with an egg or is it the stimulation that does the deed? Perhaps the article has misquoted someone?

Finding a female when all of your comrades are female is easy, but if you still need a male---what's the advantage? I would assume higher reproductive output, but there has to be a bottleneck since a male is still required.

The sperm doesn't bind with the egg, but does a series of "molecular handshakes" with the egg exterior without penetrating the egg and triggers embryogenesis. The situation isn't purely adaptive, since the species is descended from sexually reproducing ancestors and carries that baggage. Does it maximize fitness? Probably not in the long run, but if a given genome works it could be a case of if it ain't broke don't fix it. Field work has been conducted with Amazon mollies and their near relatives demonstrating that the sexually reproducing species can adapt much better to stresses like novel parasites or drought. It's still unclear what benefits a population gains by going off on such an odd adventure and abandoning meiosis/sex, going against over 2 billion years of eukaryotic cells fine-tuning meiosis (and sex as a mechanism to make it work better).

And my compliments to your mother, she needn't worry...

If there is no advantage, there might just not be a disadvantage. This species presumeably stemmed from a hybrid P. latipinna/mexicana. If the Amazons are making it by not sharing their genes because of some fluke in their makeup, and still come in contact with their "triggers," what is there to drive selection away from how they get by currently? Sure, there are local extinctions all the time with them in ditches and intermittant streams down south, I'm sure, but overall they seem to have no problem finding their "trigger" in the grand scheme.

I think a lot of oddities (and some normalities) in this world aren't selected for, but fail to be selected against.

"No selective disadvantage" is what I was trying to say in a roundabout way. Sometimes things just happen for no particularly good reason.

Gynogenesis is funky. But not as funky as kleptogenesis!

They have found a few male specimens once in a while. They are working with these to try and mate with the females to see if that has any effects. They are working bout with artificial and natural fertilization. I have not heard any results yet on this but it is interesting.

I have not heard of these. Do you have a reference or a link?

They have found a few male specimens once in a while. They are working with these to try and mate with the females to see if that has any effects. They are working bout with artificial and natural fertilization. I have not heard any results yet on this but it is interesting.