Meeting Abstract

30.8  Friday, Jan. 4  A Molecular Timescale For Snakes ALAMILLO, Hugo*; ALFARO, Michael E.; Washington State University; Washington State University halamillo@wsu.edu

Despite a rich fossil record and a flurry of recent studies of snake origins, patterns of snake diversification remain poorly understood. Many hypotheses of snake evolution, such as accelerated diversification of colubroids during the Miocene and of elapines during the Eocene, have never been rigorously evaluated. To test these and other hypotheses of ophidian diversification, we downloaded molecular sequences from one nuclear (c-mos) and two mitochondrial genes (cyt-b and 16s) for 281 snake taxa from Genbank. Chronograms were estimated in BEAST 1.45 using a Bayesian relaxed-clock model with uncorrelated log-normally distributed rates. Our analysis included 10 fossil calibrated nodes with soft upper bounds distributed broadly across our tree. Preliminary results include a Jurassic crown-age group of snakes (153 mya, 95% HPD: 126/192 mya), a Cretaceous crown age of scolecophidians (120 mya, 95% HPD: 88/159 mya), a Cretaceous split between boids and pythonids (83 mya, 95% HPD: 73/788 mya), a Paleocene (64 mya, 95% HPD: 56/70 mya) crown age of colubrids, and an Eocene crown age of elapines (46 mya, 95% HPD: 38/50 mya). We tested the hypothesis that major snake clades experienced accelerated evolution early in their history, a pattern consistent with the hypothesis of initial adaptive radiation. Using the MCCR test we found a significant slow-down in net cladogenesis for caenophidians, colubrids and elapines, consistent with hypotheses of adaptive radiation in the early history of these groups. A test based on a Kendall-Moran estimator revealed no evidence of accelerated diversification across ophidians during the Miocene. Further tests using the method of Magall�n and Sanderson to estimate absolute diversification rates of major snake clades will be reported. This research was supported in part by NSF DEB 0445453 to MEA.