A yellow-bellied water snake has, for the second year in a row, given birth without mating with a male. The snake is in captivity at the Cape Girardeau Conservation Nature Center in Missouri. This is the first example of parthenogenesis in this species of snake observed.
The snake has not been in contact with a male of her species in eight years and has twice gave birth through the process of parthenogenesis, a form of asexual reproduction. This rare process occurs when a female self fertilizes her own eggs to give birth to offspring. Because no male is involved, offspring are usually genetically identical to their mothers.
The two snakes born last year are both alive but the same can’t be said about this year’s offspring as neither survived. The death of these offspring is not surprising though; the progeny of organisms that reproduce asexually tend to have lower survival chances. The mixing of genes in sexual reproduction provides more variance among offspring increasing the odds of survival in some of them in certain conditions. Asexual reproducing organisms don’t have this advantage.
Asexual reproduction does have its advantages though. When the number of males nearby is scarce and sexual reproduction is impossible, asexual reproduction can give an individual a chance at passing on its genes. It can give birth to genetically identical offspring, which may have a chance at finding a mate in the future.
The yellow-bellied water snake can, and would likely prefer to reproduce sexually but when isolated from males for so long, asexual reproduction through parthenogenesis is better than nothing.
It is still unknown whether or not last year’s offspring can reproduce sexually but they seem to being doing well in captivity. They are on display at the Missouri Nature Centre.
While relatively common in insects, parthenogenesis is quite rare in higher animals such as snakes and no cases have been reported in mammals in the wild. It has been seen in about 10 species of snakes including one that reproduces called the brahminy blindsnake in which parthenogenesis is the only means of reproduction and females are the only sex.
While unlikely, it may be possible that the snake has been storing sperm for eight years. This is very improbable though as no species of snakes have been known to be able to carry sperm for more than a year.