Paleoclimatic and paleogeological events have been identified as being the two main drivers of genetic structuring in extant organisms. We used a montane stream-dwelling frog, Quasipaa boulengeri, to explore the relative roles played by these drivers on species in southern China, a region needing thorough studies. We detected four major matrilines, and no broadly distributed haplotypes occurred. The complex orogenesis of south-western China drove matrilineal divergence in Q. boulengeri into highly structured geographical units. These matrilines subsequently persisted in situ with stable populations rather than undergoing expansions during glacial cycling. The unification of the upper and middle Yangtze River in the Three Gorges mountain region mediated downstream colonization of this frog. Analyses identified geological events as playing a larger role than climatic fluctuations in driving the population history of Q. boulengeri. Nuclear allele analyses indicated gene flow; this maintained genetic cohesion of the species. South-eastern Sichuan Basin was identified as the area of secondary contact for several matrilines, and this area deserves further study and special protection.

Geological events play a larger role than Pleistocene climatic fluctuations in driving the genetic structure of Quasipaa boulengeri (Anura: Dicroglossidae)

Speciation remains a fundamental issue in biology. Herein, we report an investigation into speciation in the Rana chensinensis species complex using DNA sequence data from one mitochondrial and five nuclear genes. A phylogenetic analysis of the data revealed four major clades in the complex, and each of them was found to likely represent a species, including one cryptic species. Ecological niche models were generated from 19 climatic variables for three of the four major clades, which were represented by widespread sampling, including R. chensinensis, Rana kukunoris and the potential cryptic species. Each clade is associated with a unique ecological unit, and this indicates that ecological divergence probably drove speciation. Ecological divergence is likely related to the late Cenozoic orogenesis of the Qinghai-Tibetan Plateau. In addition, gene flow between species was detected but only in peripheral portions of the ranges of the four major clades, thus likely had little influence on the speciation processes. Discordances between mitochondrial and nuclear genes were also found; the nominal species, R. chensinensis, contains multiple maternal clades, suggesting potential mitochondrial introgression between R. chensinensis and R. kukunoris.

Speciation in the Rana chensinensis species complex and its relationship to the uplift of the Qinghai–Tibetan Plateau

Thirty-five years ago, the idea of a young Qinghai-Tibetan Plateau was proposed based on a comprehensive investigation on the Qinghai-Tibetan Plateau. This hypothesis suggested that the plateau began to rise from a planation surface (relict surface) that was less than 1000 m high formed during the Miocene to Pliocene. The fast uplift, i.e., the Qingzang Movement, began since ~3.6 Ma, evidenced by massive molasse deposits around the plateau margin and the synchronous occurrence of faulted basins within the plateau. However, later studies challenged this idea and suggested earlier (8, 14 or 35 Ma) formation of the huge plateau topography. Here we reevaluate the Qingzang Movement on the basis of our previous results and in light of new studies in the recent decades. The plateau margin has been subjected to intensive incision by very large drainages and shows the landscape characteristics of an “infant” stage of the geomorphological cycle. However, these drainages were not formed until 1.7–1.9 Ma; headwater erosion has not yet reached the hinterland of the plateau, so the interior of Tibet is free of significant erosion despite its lofty elevation, and remains an “old stage” landform. If the mean erosion rate is equivalent to the sum of clastic and soluble discharges of the modern rivers draining the Tibetan Plateau, it should have been worn down to a lowland within 8.6 Ma, ignoring tectonic uplift and isostasy. The massive conglomerate around the plateau margin began to deposit at about 3.6 Ma, indicating an increased relief after that time. Furthermore, the Hipparion fauna sites were widely distributed, and elephants, giraffes, and rhinos were abundant in the Qaidam Basin until the early Pliocene. Cenozoic climate change alone is not able to account for the dense occurrence of Hipparion fauna, unless the paleo-elevation of Tibet was lowered. The rise of Tibet since the Qingzang Movement has had a great influence on the Asian interior aridification.

The Qingzang movement: The major uplift of the Qinghai-Tibetan Plateau

Aim We assessed the influence of past environmental changes, notably the importance of palaeogeographical and climatic drivers, in shaping the distribution patterns of Dipodoidea (Rodentia), the superfamily most closely related to the large species-rich superfamily Muroidea (c. 1300–1500 species). Dipodoids are suitable for testing several biogeographical hypotheses because of their disjunct distribution patterns in the Northern Hemisphere and the numerous species distributed in Asian deserts. Location Holarctic. Methods We inferred molecular phylogenetic relationships for Dipodoidea (34 out of 51 species and 15 out of 16 genera) based on five coding genes. A time-calibrated phylogeny was estimated using a Bayesian relaxed molecular clock with four fossil calibrations. A cross-validation procedure was adopted to examine the impact of each fossil on our estimates. The ancestral area of origin and biogeographical scenarios were reconstructed using time-stratified dispersal–extinction–cladogenesis models. Results Phylogenetic analyses recovered a well-resolved and supported topology. The divergence between Dipodoidea and Muroidea occurred in the late Palaeocene (c. 57.72 Ma) and modern Dipodoidea diversified during the middle Eocene (c. 40.62 Ma). Similar results were found with each calibration strategy used with the cross-validation procedure. The reconstruction of ancestral areas and biogeographical events indicated that modern Dipodoidea originated in the Himalaya-Tibetan and Central Asian region. Main conclusions At the time when Dipodoidea diversified (middle Eocene), the Central Asia and Himalaya-Tibetan Plateau region experienced major uplift episodes due to the collision of India with Asia, which also induced diversification events in many other groups. Other important diversification events (e.g. divergence between Zapodidae and Dipodidae in Central Asia) took placed during the Eocene–Oligocene transition when the global temperature decreased significantly and rodent/lagomorph-dominant faunas replaced Eocene perissodactyl-dominant faunas. All of these climatic and geological disruptions in the Central Asia and Himalaya-Tibetan Plateau region modified landscapes and offered new habitats that favoured diversification events, thus triggering the evolutionary history of Dipodoidea.

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Out of Himalaya: The impact of past Asian environmental changes on the evolutionary and biogeographical history of Dipodoidea (Rodentia)

Correlation between environment and Late Mesozoic ray-finned fish evolution

Based on the phylogenetic and biogeographical studies of the glyptosternoid fishes in Qinghai-Tibet area, the following hypothesis is proposed: the speciation of this group has a direct relationship with the three uplift intervals of the Qinghai-Tibet Plateau. This process was explained by the theory of vicariance of biogeography. The ancestor of this group was similar to Bagarus and/or Glyptothorax, which still have a wide distribution. At the moment when the Tethys sea closed, the Indian tectonic plate collided with the Eurasian tectonic plate, so the Glyptothorax-like and Bagarus-like ancestors entered Eurasia and gradually became widely distributed. After the Pleistocene, with the enforced colliding, the gradual uplift of the Qinghai-Tibet Plateau brought about the current water environment, and the Glyptosternoids were generated from Glyptothorax-like fish under this environment. The present Glyptosternum, distributed across the Himalayas is the ancestor of Glyptosternoids. In the three uplift intervals of the plateau, the water system of this region was separated gradually and Glyptosternum-like ancestor was isolated in different rivers and evolved into various species. All this resulted in the speciation and formation of the biogeographical pattern of glyptosternoids.

Wenxuan Cao

Papers

The uplift of Qinghai-Xizang (Tibet) Plateau and the vicariance speciation of glyptosternoid fishes (Siluriformes: Sisoridae)