Virgin Births seen in Wild Snakes

Wednesday, September 26, 2012

Virgin births seen in wild snakes

Although facultative parthenogenesis (asexual reproduction by sexually reproducing species) have been observed in captivity in variety of species including hammerhead sharks and Komodo dragons,  until  the recent work of Dr. Warren Booth, a molecular ecologist at The University of Tulsa, it has not been observed in  wild vertebrate populations.  In two species of North American pit viper snakes, copperheads and cottonmouths, females were detected that delivered offspring without mating with males (i.e., embryonic development occurred without fertilization from sperm). 

female copperhead with offspring

In recent work published in the Royal Society journal Biology Letters, Dr. Booth examined microsatellite DNA genotypes (a form of DNA fingerprinting) from captured pregnant females and their offspring. The results revealed that both species of pitviper snake are capable of reproducing via facultative parthenogenesis (commonly referred to as virgin births). In 22 copperhead litters and 37 cottonmouth litters, in each species a single litter contained parthenogenetic offspring. Each parthenogenetic litter consisted of a single male offspring, composed of half of its mother’s genetic material.  The rate of such births suggests that between 2.5 to 5.0 percent of litters in these wild reptiles may be produced by facultative parthenogenesis.

Why would a species which typically produces offspring by sexual reproduction also retain the capacity of asexual reproduction?  Being able to switch to from sexual to parthenogenetic modes of reproduction may allow females in the absence of males to perpetuate the species.  However, in the habitats from which these species were collected males were present alongside the females. Given the lack of reproductive information relating to each female, it is impossible to determine whether or not they had previously mated, and in each case rejected the sperm of the male. Given the diminutive size of the copperhead in this study, it is possible that the mate-seeking males, simply overlooked her in favor of larger, more fecund females. Other environmental factors, including  bacterial infections, are known to influence reproductive mode in a number of invertebrate species. Their role in vertebrate parthenogenesis is currently unknown, however this is a line of research Dr. Booth is presently investigating.

Can facultative parthenogenesis in reptiles result in viable offspring which can grow to maturity and pass on their genes to succeeding generations.  If so, what is the evolutionary impact of facultative parthenogenesis? Organisms reproducing asexually typically have reduced genotypic diversity when compared to out-breeding sexual species and this may potentially limit their fitness and ability to adapt to shifts in environmental conditions. Many interesting avenues of research can be explored if these virgin births can be demonstrated as a viable form of reproduction and not a reproductive error as previously considered.

Warren Booth