The East Asian monsoon drove the latitudinal expansion and convergent adaptation of true frogs to overwintering
Past and present climates are prominent drivers of phylogeographic diversity and the evolution of ecological traits, especially for species distributed across latitudinal gradients. Subsequent to the ancient Holarctic true frogs (Rana spp.) dispersed out of Asia and into the Nearctic because of geological events, we provided evidences that evolution of the modern East Asian monsoon and climate variability since the Neogene period were the factors driving the present diversity of the genus in the Palearctic. Specifically, the resulting latitudinal climate diversity concurrently triggered the evolution of trait related to latitudinal range extent and adaptability of a subarctic Eurasian clade to overwintering. We integrated a meta-analysis and climatic variables in phylogenetic comparative methods, then merged quantitative taxonomy and multilocus phylogeography to: (i) track the evolutionary history of latitudinal ranges in Ranidae widespread across the Holarctic and Indomalayan realms, (ii) resolving the evolutionary diversifications of Rana distributed across the Palearctic (348 individuals sampled; 17 species and 52 localities). The phylogenetic signal and the ancestral character states demonstrated the significant association between annual precipitation and the homoplasy in the extend of latitudinal ranges in ranids. Specifically, the trait was prevalent among opportunistic species (e.g., Pelophylax ridibundus) and other Eurasian subarctic species (e.g., Rana amurensis, Rana dybowskii and Rana temporaria) c. 30.0 Mya, and accumulated in Nearctic ranids (e.g., Lithobates catesbeianus, Lithobates sylvaticus) c. 12.0 Mya. Paleogeographic models further provided support to the joint impact of the East Asian monsoon changes and Arctic oscillations on the diversification of three major stem lineages and repeated sub-radiations of East Asian Rana in central latitudes since 22.0 Mya. Finally, we demonstrated the dispersal of northern R. amurensis clades into the Siberian-subarctic c. 7.7 Mya, coinciding with warmer-than-today conditions of the Arctic in the Late Miocene, and exemplifying climate-induced gradual adaptation to the present extremely cold subarctic conditions.
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