Friday, April 26, 2019

[Herpetology • 2019] The Origins and Diversification of the Exceptionally Rich Gemsnakes (Colubroidea: Lamprophiidae: Pseudoxyrhophiinae) in Madagascar


Phylogeny of Pseudoxyrhophiinae.  

in Burbrink, Ruane, Kuhn, Rabibisoa, Randriamahatantsoa, et al., 2019. 
  DOI: 10.1093/sysbio/syz026  

Abstract
Processes leading to spectacular diversity of both form and species on islands have been well documented under island biogeography theory, where distance from source and island size are key factors determining immigration and extinction resistance. But far less understood are the processes governing in-situ diversification on the world’s mega islands, where large and isolated land masses produced morphologically distinct radiations from related taxa on continental regions. Madagascar has long been recognized as a natural laboratory due to its isolation, lack of influence from adjacent continents, and diversification of spectacular vertebrate radiations. However, only a handful of studies have examined rate shifts of in-situ diversification for this island. Here we examine rates of diversification in the Malagasy snakes of the family Pseudoxyrhophiinae (gemsnakes) to understand if rates of speciation were initially high, enhanced by diversification into distinct biomes, and associated with key dentition traits. Using a genomic sequence-capture dataset for 366 samples, we determine that all previously described and newly discovered species are delimitable and therefore useful candidates for understanding diversification trajectories through time. Our analysis detected no shifts in diversification rate between clades or changes in biome or dentition type. Remarkably, we demonstrate that rates of diversification of the gemsnake radiation, which originated in Madagascar during the early Miocene, remained steady throughout the Neogene. However, we did detect a significant slowdown in diversification during the Pleistocene. We also comment on the apparent paradox where most living species originated in the Pleistocene, despite diversification rates being substantially higher during the earlier 15 million years.

Key Words: Pseudoxyrhophiinae, gemsnakes, island biogeography, in situ diversification, speciation, Neogene

Distribution of pairwise divergence dates for 36 newly discovered species pairs (blue) against previously described species pairs (pink) using BPP.

Phylogeny of Pseudoxyrhophiinae, with photographs showing representative species from all included Madagascan genera.
Distribution of pairwise divergence dates for 36 newly discovered species pairs (blue) against previously described species pairs (pink) using BPP.


Frank T. Burbrink, Sara Ruane, Arianna Kuhn, Nirhy Rabibisoa, Bernard Randriamahatantsoa, Achille P. Raselimanana, Mamy S. M. Andrianarimalala, John E. Cadle, Alan R. Lemmon, Emily Moriarty Lemmon, Ronald A. Nussbaum, Leonard Jones, Richard Pearson and Christopher J. Raxworthy. 2019. The Origins and Diversification of the Exceptionally Rich Gemsnakes (Colubroidea: Lamprophiidae: Pseudoxyrhophiinae) in Madagascar. Systematic Biology. syz026.  DOI: 10.1093/sysbio/syz026


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