Seemingly just in time for Christmas, a recent news story via The Australian tells of a problem of invasive mourning geckos. Invasive species are a problem anywhere they show up, and Australia has had many problems with invasive critters in the past, but this problem is different as these geckos are entirely female. That’s right, much like the whiptail lizards of the U.S., this species is apparently entirely made up of females that can fertilize their own eggs, doubling the reproduction rate. This has important ramifications for ecological and evolutionary patterns, especially in terms of Founder Effect, which is the effect of a new population being established by a small number of individuals. Think of it this way, the mourning geckos (only requiring females to reproduce) somehow catch a lift on a piece of flotsam to an island not far away, are released by a collector that can’t keep them, or catch a lift by boat or plane. Provided the geckos survive their trip and find habitat on the island, they can readily reproduce and the population will grow at a higher rate than endemic species requiring sexual reproduction being that all the offspring are females and all females can reproduce. This seems to be an effective short-term strategy, and there is some genetic difference between mother and daughters (the daughters are not clones), but the net genetic difference that sexual reproduction allows for is reduced. Thus, the species may not be as likely to adapt to quick ecological changes or have natural selection work on changes brought about through random mutation. The converse of this is that since there is less random mutation as a result as sexual reproduction, there are less harmful mutations and the species is more stable, but again this strategy may be a downfall in the long term. In essence it’s a trade off, exchanging genetic variability for reproductive success, having both pros and cons to the process, as well as having little change from the parent population making parthenogenic creatures like these geckos unlikely candidates for rapid evolutionary change through punctuated equilibrium.
I searched PubMed for mourning geckos or any information on what precisely is happening in their sexual cycle, but the only article that came up involved intestinal parasites, and the article that led me to this story in the first place is ambiguous, suggesting that the females have made their “male counterpart[s] redundant.” If this were true, that the females have spurned their male partners to reproduce on their own, it would be an amazing evolutionary event, but this does not appear to be the case. Upon a further Google search for “mourning gecko + male”, it appears that male mourning geckos are unknown, the closest thing to a male being “bisexual” females. I haven’t found any reference to how these females are “bisexual” either, but from what I understand I’m assuming that the mourning gecko’s reproductive cycle is akin to that the the whiptail lizards, in that some females mount other females during certain times of the year. Although one female can not fertilize another (nor does one need to), the copulation seems to increase certain hormone levels that result in greater reproductive success, so while they are parthenogenic in their reproductive cycle sex still plays an important role.
Whenever I go to the zoo, there are always parents telling their children how a mommy bear and a daddy bear make a baby bear, or how the mama tiger takes care of her cubs, playing into the anthropomorphism common when it comes to most animals; explaining parthenogenesis or gay penguins or any of natures vast reproductive strategies would most likely only further confuse parent and child. Even so, there is a view that all “higher” animals (chordates on up) have the strongest males breeding with the most viable females, making it easy to generalize about how reproduction happens. Unfortunately for the uninformed, most organisms do not reproduce as we do, using a vast array of behaviors and appendages that would seem alien if we did not observe them among extant taxa. I can only imagine what the reproductive strategy of extinct organisms like Stegosaurs must have been like, although I’m sure the old adage of “very carefully” would describe how such spiny behemoths went about their intimate affairs.