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Eurasia is a large continent characterized by heterogeneous environments. Glacial cycles during the late Pleistocene have had variable impacts on the avifauna across Eurasia. Bird populations from South-East Asia show stability through the Last Glacial Maximum ( LGM), while populations from Europe exhibit evidence of post- LGM expansion. We investigated the phylogeography of the Long-tailed Tit ( Aegithalos caudatus), which spans the longitudinal breadth of Eurasia to test how climatic history and regional topographical complexity affected populations and diversification within the species complex. Our results show that two lineages from central and southern China (lineages C and D) segregate geographically, while lineages across northern Eurasia (lineage A and B) show substantial sympatry. Bayesian estimates for the timing of diversification suggest that the four lineages diverged during the middle Pleistocene, splitting in parallel and undergoing concurrent demographic histories since divergence. A. caudatus lineages experienced similar and synchronous population size dynamics during glacial cycles before the LGM. We conclude that the difference in geo-topologic complexity may be an important factor that led to the variation in secondary admixture between northern Eurasian and eastern Asian lineages. [ABSTRACT FROM AUTHOR]

Genetic diversity is one of the three dimensions of biodiversity and fundamental to various life forms on the Earth. Understanding the distribution pattern of genetic diversity and its driving forces has been an important topic in ecology, biogeography and conservation biology since the last decade. We investigated the genetic diversity pattern of passerine birds in the Mountains of Southwest China, a global biodiversity hotspot with the highest species richness of birds in the entire Eurasia, and explored the influencing forces of environmental variables on genetic diversity. We compiled 1189 Cytochrome b sequences of 27 passerine species from 152 geographic sites, covering the range of Mountains of Southwest China and its adjoining areas. We generated genetic diversity distribution maps using a grid-cell method based on nucleotide diversity and haplotype diversity indices. We further analyzed the variation pattern of the two indices along latitudinal, longitudinal, and elevational gradients. The correlations between the two indices and environmental variables were also evaluated. The nucleotide diversity hotspots were mostly located in the southern Hengduan Mountains, while for haplotype diversity, three hotspots were detected: the southeast edge of the Qinghai-Tibetan Plateau, the southern Hengduan Mountains and the Qinling Mountains. There was no monotonic increasing or decreasing pattern in nucleotide diversity or haplotype diversity along latitudinal, longitudinal or elevational gradients except for altitudinal range. Correlation and model selection analyses detected multiple environmental variables in driving genetic diversity patterns, including temperature, precipitation, vegetation, human influence, longitude and altitude range. Similar to the pattern of species richness, the nucleotide diversity pattern of passerine birds in the Mountains of Southwest China presents a decreasing trend from southwest to northeast, while the haplotype diversity pattern is more likely decreased from west to east. Our results indicate that the distribution pattern of genetic diversity may be derived from the complex topography and diverse microclimates in the Mountains of Southwest China. [ABSTRACT FROM AUTHOR]