The Emerging Phylogenetic Pattern of Parthenogenesis in Snakes

 

Booth, Warren                                      

Department of Biological Sciences                                                                                               

The University of Tulsa, Tulsa, OK USA

 

Schuett, Gordon W.                                                                                                                 

Department of Biology and Neuroscience Institute                                                                      

Georgia State University, Atlanta, GA USA

 

Chiricahua Desert Museum & Geronimo Event Center                                                          

Rodeo, NM USA      

 

 

Parthenogenesis has been documented across a variety of vertebrate taxa. Within snakes, a group for which the largest number of cases has been documented, both obligate and facultative types of parthenogenesis exists, although the obligate form appears to be restricted to a single species of blind snake, Indotyphlops braminus. By contrast, a number of snake species that otherwise reproduce sexually have been found 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 as 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. In light of the growing number of documented cases of parthenogenesis, it is now possible to review the phylogenetic distribution in snakes and thus identify subtle variations and commonalities that may exist through the characterization of its emerging properties. Based on our findings, we propose partitioning facultative parthenogenesis in snakes into two categories, type A and type B, based on the sex of the progeny produced, their viability, sex chromosome morphology, ploidy, phylogenetic position. Furthermore, we introduce a hypothesis (directionality of heterogamety hypothesis) to explain the production of female-only parthenogens in “primitive” snakes (basal alethinophidians) and male-only parthenogens in “advanced” snakes (caenophidians).