Molecular genetic evidence for parthenogenesis in the Burmese python, Python molurus bivittatus

Abstract

Parthenogenesis among reptiles is rare. Only a few species have the ability to reproduce asexually. Most of these are obligate parthenogenetic species that consist (almost) entirely of females, which can reproduce solely through parthenogenesis. Rarer are sexual species that only sporadically reproduce through parthenogenesis. A female Python molurus bivittatus (Reptilia, Boidae) from the Artis Zoo, Amsterdam, produced eggs in five consecutive years that contained embryos while she was isolated from males. These eggs might be fertilized with stored sperm, or might be the product of parthenogenesis. Parthenogenesis has not been shown for the Boidae family before. We performed parentship analyses on the snake and seven of her embryos using microsatellites and AFLP. Four microsatellite loci developed for this species combined with three loci developed previously for different snake species revealed too little variation to discriminate between sperm retention and parthenogenesis. With AFLP we were able to confirm that the Artis Zoo female reproduced parthenogenetically. Because the offspring are genetically identical to their mother, whereas in previous studies on sporadic parthenogenesis in snakes a loss of genetic information was reported, we conclude that the meiotic pathways that produce the diploid egg cells are different.

Evidence for viable, non-clonal but fatherless Boa constrictors

“…As the offspring are nonclonal, limited intra-litter variation will exist, however, owing to maternal heterozygosity at some loci. Previous studies suggest that only ZZ zygotes resulting in male offspring will develop [3,5,6,12,20]; however, their long-term viability is unknown as many fail to hatch or are stillborn (e.g. [5]).…”

“…This single parthenogenetic event recorded in the Pythonidae resulted in embryos with levels of heterozygosity comparable to that of the mother [3]. Although genic heterozygosity is retained, essentially comparable to that of the mother, habitual parthenogenetic reproduction will eventually lead to the accumulation of deleterious mutations through the lack of recombination (e.g.…”

“…the fusion of the second polar body with the egg nucleus during meiosis, resulting in extensive homozygosity; [5,6,11,12]), or females (ZW) following apomixes, premeiotic doubling or automictic central fusion (i.e. fusion of the first polar body with the oocyte during meiosis, preserving maternal heterozygosity; [3,13]). Among the primitive snakes of the families Boidae (Boas) and Pythonidae (Pythons), anecdotal reports of parthenogenetic reproduction exist, but only one instance has been scientifically demonstrated [3].…”

“…fusion of the first polar body with the oocyte during meiosis, preserving maternal heterozygosity; [3,13]). Among the primitive snakes of the families Boidae (Boas) and Pythonidae (Pythons), anecdotal reports of parthenogenetic reproduction exist, but only one instance has been scientifically demonstrated [3]. Apparently fertile eggs produced by an isolated Burmese Python (Python molurus bivittatus) were partially incubated before embryo dissection for genetic screening and sexing.…”

Evolutionary perspectives on clonal reproduction in vertebrate animals

“…In recent years, several instances of sporadic parthenogenesis (tychoparthenogenesis) have come to light in species that otherwise reproduce sexually. For example, in the Burmese snake, Python molurus (22), and in the Bonnethead shark, Sphyrna tiburo (23), captive specimens without known access to males occasionally have given virgin birth to progeny that have proved on molecular examination to be genetically identical to their one and only female parent. I strongly suspect that many additional instances of tychoparthenogenesis (either meiotic or ameiotic) have gone unnoticed in nature simply because suitable molecular markers have not been systematically deployed to address possible clonal identities in large numbers of individuals from most natural vertebrate populations.…”