Once again, we look at livebearers. Not only do they look after young internally and have the ability to change sex, one particular species within this group does away with sexual reproduction completely! The Amazon molly (Poecilia formosa) is described as a unisex species with all individuals being female. From a genetic point of view, a typical egg cell from most animals contains only half of the genetic material to create a viable embryo, with the other half of the genetic material being provided by a male of the same species. This introduces a small amount of genetic variation amongst offspring; some of that variation being favourable to survival, some not. Those that survive pass on these beneficial traits to the next generation and so on. The all-female Amazon molly deviates from this strategy in that the eggs she produces (and subsequently incubates internally) contain all of the genetic material, which is just as well as there are no male fish to provide their contribution. In a strange twist of biology, mating is still required to get the process of egg development underway. But how can this happen if there are no males within this species? Well, from males from very closely related species! More recently, it has been discovered that these interspecies matings do allow for a very small amount of genetic variation to occur to provide the benefits that genetic mixing bring. Now if that’s not a bizarre lifecycle, I don’t know what is!
Image credit: furity.org
Tagged in: Aquatic Adaptations