Partitioned Bayesian analyses, dispersal-vicariance analysis, and the biogeography of Chinese toad-headed lizards (Agamidae: Phrynocephalus): a re-evaluation.

The toad-headed lizards of genus Phrynocephalus are distributed from northwestern China to Turkey and are one of the major components of the central Asian desert fauna. To date, published morphological and molecular phylogenetic hypotheses of Phrynocephalus are only partially congruent, and the relationships within the genus are still far from clear. We re-analyzed published mitochondrial gene sequence data (12S, 16S, cyt b, ND4-tRNA(Leu)) by employing partition-specific modeling in a combined DNA analysis to clarify existing gaps in the phylogeny of Chinese Phrynocephalus. Using this phylogenetic framework, we inferred the genus' historical biogeography by using weighted ancestral-area analysis and dispersal-vicariance analysis in combination with a Bayesian relaxed molecular-clock approach and paleogeographical data. The partitioned Bayesian analyses support the monophyly of Phrynocephalus and its sister-group relationship with Laudakia. An earlier finding demonstrating the monophyly of the viviparous group is corroborated. However, our hypothesis of internal relationships of the oviparous group differs from a previous hypothesis as our results do not support monophyly of the oviparous taxa. Instead, the viviparous taxa form a clade with many oviparous taxa exclusive of P. helioscopus and P. mystaceus. Our results also suggest that: (1) P. putjatia is a valid species, comprising populations from Guide, Qinghai Province and Tianzhu, Gansu Province; (2) P. hongyuanensis is not a valid species, synonymized instead with P. vlangalii; (3) P. zetangensis is not a valid species and should be included in P. theobaldi; (4) the population occurring in Kuytun, Xinjiang Uygur Autonomous Region is recognized as P. guttatus instead of P. versicolor; and (5) the Lanzhou population of P. frontalis is part of P. przewalskii. Congruent with previous hypotheses, the uplift of the Tibetan Plateau played a fundamental role in the diversification of Phrynocephalus. An evolutionary scenario combining aspects of vicariance and dispersal is necessary to explain the distribution of Phrynocephalus. Bayesian divergence-time estimation suggests that Phrynocephalus originated at the Middle-Late Miocene boundary (15.16-10.4 Ma), and diversified from Late Miocene to Pleistocene from a center of origin in Central Asia, Tarim Basin, and Junggar Basin temperate desert, followed by several rapid speciation events in a relatively short time. The proposed biogeographic scenarios also indicate that the Tarim Basin desert may be the secondary diversification center, followed by Junggar Basin temperate desert and Alashan Plateau temperate desert. In the viviparous group, the allopatric speciation of P. theobaldi and P. vlangalii may have been caused by the uplifting of Tanggula Mountain Ranges. In addition, the results of this study make an important contribution to understanding the uplift of the Tibetan Plateau and Tian Shan Mountains and the biogeography of the entire region.