Phylogenetic relationships and origin of the rattlesnakes of the Gulf of California islands (Viperidae: Crotalinae: Crotalus)

The islands of the Gulf of California are divided into three categories – oceanic, continental, and landbridge – and were formed from the Middle Miocene to the Holocene. The species of the Crotalus genus are an important ecological element of the endemic fauna of these islands. This study is the first to include several island-endemic species in a phylogenetic framework. We seek to understand the phylogenetic relationships among these species, and in particular, whether these species are more related to the Baja California peninsula or continental Mexican species, and whether the divergence times for these relationships are consistent with the formation of the islands. We performed a phylogenetic analysis and estimated divergence times using Bayesian inference and two mitochondrial 12S and 16S genes. The analyses show a new relationship between Crotalus angelensis and C. pyrrhus. Crotalus lorenzoensis was nested with C. ruber individuals, making this species a paraphyletic species. A novel relationship was also detected in that C. estebanensis was sister to C. basiliscus. The divergence time for all island-endemic Crotalus species is consistent with the formation of these islands. In addition, the insular species are related to their congeners in the Baja California peninsula or mainland Mexico.