Sunday, September 25, 2011

Novel Squamates

In the 1970's I remember several conversations with zoo curators and reptile keepers who swore female snakes would give birth to offspring without ever being in the presence of a male or if they had been with a male it had been years before the offspring/eggs developed. The latter situation was often attributed to sperm storage. At the time, I was skeptical, but parthenogenesis was known in lizards since Ilya Darevsky discovered all female rock lizard, Lacerta saxicola, populations in 1958 in southern Russia. L. saxicola (Eversmann, 1834) has now been removed from Lacerta and placed in the genus Darevskia, with about 25 other species of rock lizards, the generic name derived from the name of the Russian herpetologist. But, four decades later parthenogenesis has been documented in many squamates, and it has apparently evolved at least 40 times independently. 
Squamate reptiles (lizards + snakes) are both numerous and diverse with 61 families and more than 9000 species. With the diversity come novel traits that have evolved multiple times - like parthenogenesis. In a forthcoming paper Sites et al. (2011) summarize many of these novel traits in squamates - traits like parthenogenetic, viviparity, limb-reduction and limb loss, herbivory, and venom. The authors note that squamates are the only vertebrate group with true parthenogenesis; the clade has more origins of viviparity than any other group of vertebrates; and squamates have undergone dramatic changes in body form (lizard-like to snake-like) dozens of times.

They also note that new phylogenetic hypotheses are challenge our ideas about squamate biology and are emerging at all taxonomic levels. Phylogeny based research is revealing much about ecological aspects of of parthenogenesis as well as finer details about the origins of several forms of viviparity.

Sites, J. W., Jr, T. W. Reeder, J. J. Wiens. 2011. Phylogenetic Insights on Evolutionary Novelties in Lizards and Snakes: Sex, Birth, Bodies, Food, and Venom. Annual Review of Ecology, Evolution, and Systematics, DOI: 10.1146/annurev-ecolsys-102710-145051

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