Do rivers function as genetic barriers for the plateau wood frog at high elevations?

Phylogeographic inference of Sumatran ranids bearing gastromyzophorous tadpoles with regard to the Pleistocene drainage systems of Sundaland

Rivers are known to act as biogeographic barriers in several strictly terrestrial taxa, while possibly serving as conduits of dispersal for freshwater-tolerant or -dependent species. However, the influence of river systems on genetic diversity depends on taxa-specific life history traits as well as other geographic factors. In amphibians, several studies have demonstrated that river systems have only minor influence on their divergence. Here, we assess the role of the paleodrainage systems of the Sunda region (with a focus on the island of Sumatra) in shaping the evolutionary history of two genera of frogs (Sumaterana and Wijayarana) whose tadpoles are highly dependent on cascading stream habitats. Our phylogenetic results show no clear association between the genetic diversification patterns of both anurans genera and the existence of paleodrainage systems. Time-calibrated phylogenies and biogeographical models suggest that these frogs colonized Sumatra and diversified on the island before the occurrence of the Pleistocene drainage systems. Both genera demonstrate phylogenetic structuring along a north–south geographic axis, the temporal dynamics of which coincide with the geological chronology of proto Sumatran and -Javan volcanic islands. Our results also highlight the chronic underestimation of Sumatran biodiversity and call for more intense sampling efforts on the island.

Mountains too high and valleys too deep drive population structuring and demographics in a Qinghai-Tibetan Plateau frog Nanorana pleskei (Dicroglossidae)

Pleistocene glacial–interglacial climatic oscillations greatly shaped the current genetic structure of many species. However, geographic features may influence the impact of climatic cycling. Distinct geographic and environmental characters between northern and southern parts of the eastern Qinghai–Tibetan Plateau (EQTP) facilitate explorations into the impacts of geographic features on species. The northern parts of EQTP contain large areas of marsh, and the environment is rather homogeneous. In contrast, the southern EQTP harbors complex alpine valleys and a much more heterogeneous setting. We evaluate DNA sequence variation from both the mitochondrial and nuclear genomes in Nanorana pleskei, a species endemic to the EQTP. Hypothesis testing on the evolutionary history of N. pleskei indicates that northern populations can disperse freely, but alpine valleys isolate southern populations. Demographic histories between northern and southern populations also differ. Northern populations appear to have experienced population expansions, while southern frogs exhibit a far more stable demographic history. By combining climatic analyses and species' distribution models, our study suggests that geographic and environmental features drive the differences between the northern and southern EQTP.

Yangtze River, an insignificant genetic boundary in tufted deer (Elaphodus cephalophus): the evidence from a first population genetics study

Great rivers were generally looked at as the geographical barrier to gene flow for many taxonomic groups. The Yangtze River is the third largest river in the world, and flows across South China and into the East China Sea. Up until now, few studies have been carried out to evaluate its effect as a geographical barrier. In this study, we attempted to determine the barrier effect of the Yangtze River on the tufted deer (Elaphodus cephalophus) using the molecular ecology approach. Using mitochondrial DNA control region (CR) sequences and 13 nuclear microsatellite loci, we explored the genetic structure and gene flow in two adjacent tufted deer populations (Dabashan and Wulingshan populations), which are separated by the Yangtze River. Results indicated that there are high genetic diversity levels in the two populations, but no distinguishable haplotype group or potential genetic cluster was detected which corresponded to specific geographical population. At the same time, high gene flow was observed between Wulingshan and Dabashan populations. The tufted deer populations experienced population decrease from 0.3 to 0.09 Ma BP, then followed by a distinct population increase. A strong signal of recent population decline (T = 4,396 years) was detected in the Wulingshan population by a Markov-Switching Vector Autoregressions(MSVAR) process population demography analysis. The results indicated that the Yangtze River may not act as an effective barrier to gene flow in the tufted deer. Finally, we surmised that the population demography of the tufted deer was likely affected by Pleistocene climate fluctuations and ancient human activities.

The Phylogeography and Population Demography of the Yunnan Caecilian (Ichthyophis bannanicus): Massive Rivers as Barriers to Gene Flow

Ichthyophis bannanicus is the only caecilian species in China. In this study, the phylogeography and population demography of I. bannanicus were explored, based on the mitochondrial DNA genes (cyt b and ND2) and 15 polymorphic microsatellite loci. Altogether 158 individuals were collected from five populations in Yunnan province, Guangxi province, Guangdong province, and Northern Vietnam. Phylogeographical and population structure analysis identified either two groups (Xishuangbanna, Northern Vietnam-Yulin-Yangchun-Deqing) or three groups (Xishuangbanna, Northern Vietnam-Yulin-Yangchun, and Deqing), indicating that the Red River and Pearl River systems may have acted as gene-flow barriers for I. bannanicus. Historical population expansion that happened 15–17 Ka ago was detected for mtDNA data and was possibly triggered by warmer weather after the Last Glacial Maximum. However, the Bayesian simulations of population history based on microsatellite data pinpointed population decline in all populations since 19,123 to 1,029 years ago, demonstrating a significant influence of anthropogenic habitat alteration on I. bannanicus.

The Sepik River (Papua New Guinea) is not a dispersal barrier for lowland rain-forest frogs

Major tropical rivers have been suggested to be important dispersal barriers that increase the beta diversity of animal communities in lowland rain forests. We tested this hypothesis using assemblages of frogs in the floodplains of the Sepik River, a major river system in Papua New Guinea. We surveyed frogs at five sites within a continuous 150 × 500-km area of lowland rain forest bisected by the Sepik, using standardized visual and auditory survey techniques. We documented 769 frogs from 44 species. The similarity in species composition decreased with logarithm of geographical distance between the sites, which ranged from 82 to 465 km. The similarity decay did not depend on whether or not the compared sites were separated by the Sepik River or whether the species were aquatic or terrestrial breeders. Likewise, a DCA ordination of frog assemblages did not show separation of sites by the river as a significant factor explaining their composition. Our results suggest that even major rivers, such as the Sepik, may not act as dispersal barriers. Rivers may not limit the distribution of frogs and therefore have a limited effect on determining frog species abundance and assemblage structure in rain forests.