Saturday, May 19, 2018

[Herpetology • 2018] Molecular Systematics and Historical Biogeography of the Genus Gerrhonotus (Squamata: Anguidae)

in García‐Vázquez, Nieto‐Montes de Oca, Bryson, et al. 2018. 
   DOI: 10.1111/jbi.13241 

Multiple geological and climatic events have created geographical or ecological barriers associated with speciation events, playing a role in biological diversification in Mexico. Here, we evaluate the influence of Neogene geological events and of Pleistocene climate change in the diversification of the genus Gerrhonotus using molecular dating and ancestral area reconstruction.

Location: Mexico and south‐central United States.

A multilocus sequence dataset was generated for 86 individuals of Gerrhonotus from most Mexican biogeographical provinces and belonging to five of the seven currently recognized species, as well as two putative undescribed species. Phylogeographical structure was explored using Poisson‐Tree‐Processes molecular species delimitation. Divergence events were estimated based on the fossil record using a relaxed uncorrelated lognormal clock. Ancestral areas were estimated at divergence events across the tree using a probabilistic Bayesian approach.

Extensive geographical structure was evident within three well‐supported clades. These clades probably diverged from each other in the early to mid‐Miocene, and their divergence was followed by six divergences in the late Miocene and eight divergences in the Pliocene. The ancestral origin of Gerrhonotus with keeled dorsal scales (keeled‐scale Gerrhonotus) was reconstructed to be across the Pacific Coast Province. Our phylogenetic analyses did not support the monophyly of Gerrhonotus.

Main conclusions: 
Miocene and Pliocene geomorphology, perhaps in conjunction with climate change, appears to have induced allopatric divergence on a relatively small spatial scale in this genus. The late Miocene–Pliocene reduction in the highlands along the Tehuantepec fault probably created a large marine embayment that led to an early divergence in a clade of Gerrhonotus. Our analysis suggests uplifting of the Trans‐Mexican Volcanic Belt during this same time period resulted in additional diversification. This was followed by more recent, independent colonization events in the Pliocene from the Mexican Plateau to the Sierra Madre Oriental, Sierra Madre Occidental, Tamaulipas and Edwards Plateau provinces. A genus Gerrhonotus with the keeled‐scale species in addition to Coloptychon rhombifer (= G. rhombifer) is strongly supported. Inclusion of the smooth dorsal‐scale species in the genus is uncertain and maintained only tentatively.

Keywords: ancestral area reconstruction, Coloptychon,  divergence dating, diversification, Gerrhonotus, Isthmus of Tehuantepec, Mexican Plateau, Trans‐Mexican Volcanic Belt

Biogeographical studies seek to explain the distributions of species in terms of historical factors and contemporary ecology. The genus Gerrhonotus has proven to be an insightful model for studying these factors in a widely distributed group. Extreme climatic oscillations during the Pleistocene, a key driver of diversification between lineages in some taxa (León‐Paniagua et al., 2007), do not appear to have substantially affected diversification in Gerrhonotus. Instead, Miocene and Pliocene geomorphology, perhaps in conjunction with climate change, appears to have induced allopatric divergence on a relatively small spatial scale in this genus. There is strong support for a genus Gerrhonotus composed of the keeled‐scale species in the genus in addition to Coloptychon rhombifer (= G. rhombifer), whereas inclusion of the smooth‐scale Gerrhonotus into the genus should be regarded as tentative. Gerrhonotus infernalis, G. liocephalus and G. ophiurus may each be composed of multiple evolutionary independent lineages.

Uri O. García‐Vázquez, Adrián Nieto‐Montes de Oca, Robert W. Bryson Jr., Walter Schmidt‐Ballardo and Carlos J. Pavón‐Vázquez. 2018. Molecular Systematics and Historical Biogeography of the Genus Gerrhonotus (Squamata: Anguidae). Journal of Biogeography.  DOI: 10.1111/jbi.13241

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