Snakes: A Model System for Studying Facultative Parthenogenesis of Vertebrates

Booth, Warren

Department of Biological Science

The University of Tulsa

Tulsa, OK 74104 USA

Schuett, Gordon W.

Department of Biology and Neuroscience Institute

Georgia State University

Atlanta, GA 30303 USA

Chiricahua Desert Museum

P.O. Box 376

Rodeo, NM 88056 USA

Card, Daren C.

Department of Biology

University of Texas — Arlington

Arlington, TX 76019 USA

Parthenogenesis is widespread in animal taxa, including vertebrates. Within squamate reptiles (lizards and snakes), a group for which the largest number of cases is documented, both obligate and facultative types of parthenogenesis exists; however, the obligate form in snakes appears to be restricted to a blind snake, Indotyphlops braminus (scolecophidian). By contrast, a number of snake species that otherwise reproduce sexually are capable of facultative parthenogenesis. Because the original documentation of this phenomenon was restricted to subjects held in captivity and isolated from males, facultative parthenogenesis was attributed to be a captive syndrome. However, its recent discovery in nature shifts the paradigm and identifies this form of reproduction as a potentially important feature of vertebrate evolution. With the growing number of documented cases of parthenogenesis in snakes and the development of robust phylogenies, it is possible to provide a reasonable phylogenetic distribution of facultative parthenogenesis (and associated characters) and identify subtle variations and commonalities that may exist through the characterization of its emerging properties. Accordingly, based on our recent phylogenetic analyses, we partitioned facultative parthenogenesis in snakes into type A and type B categories divided by phylogenetic position, sex of the parthenogens, viability, and sex chromosome morphology. Recently, we introduced the directionality of heterogamety hypothesis, which seeks to explain the production of female-only parthenogens in primitive (basal alethinophidian snakes) and male-only parthenogens in advanced (caenophidian) snakes. We provide RADseq (restriction-site associated DNA sequencing) derived data supporting this in both Boa (Boidae) and Python (Pythonidae). Through additional RADseq analysis, we describe our recent collaborative analyses of genome-wide variation in parthenogens produced within the same reproductive event relative to their sexually-produced mother in the Boa Constrictor (Boa imperator) and King Cobra (Ophiophagus hannah). Importantly, heterozygosity is restored following sexual reproduction of a parthenogen with an unrelated male in Boa imperator.