Phylogenetic surveys on the newt genus Tylototriton sensu lato (Salamandridae, Caudata) reveal cryptic diversity and novel diversification promoted by historical climatic shifts

Abstract

Global climatic transitions and Tibetan Plateau uplifts are hypothesized to have profoundly impacted biodiversity in southeastern Asia. To further test the hypotheses related to the impacts of these incidents, we investigated the diversification patterns of the newt genus Tylototriton sensu lato, distributed across the mountain ranges of southeastern Asia. Gene-tree and species-tree analyses of two mitochondrial genes and two nuclear genes revealed five major clades in the genus, and suggested several cryptic species. Dating estimates suggested that the genus originated in the early-to-middle Miocene. Under different species delimitating scenarios, diversification analyses with birth-death likelihood tests indicated that the genus held a higher diversification rate in the late Miocene-to-Pliocene era than that in the Pleistocene. Ancestral area reconstructions indicated that the genus originated from the northern Indochina Peninsula. Accordingly, we hypothesized that the Miocene Climatic Transition triggered the diversification of the genus, and the reinforcement of East Asian monsoons associated with the stepwise uplifts of the Tibetan Plateau promoted the radiation of the genus in southeastern Asia during the Miocene-to-Pliocene period. Quaternary glacial cycles likely had limited effects on speciation events in the genus, but mainly had contributions on their intraspecific differentiations.

Integrative taxonomy reveals three new taxa within the Tylototriton asperrimus complex (Caudata, Salamandridae) from Vietnam

“…In this case the genetic differences of taxon 3 to the topotypical population of T. asperrimus ranged between 4.1 to 4.2 % to taxon 1 between 3.6 to 4.0 %, and to taxon 2 between 4.1 to 4.5 % (see Table 2 for genetic distances). Our time estimates are very similar to those generated by Wang et al (2018), and the results show that T. asperrimus from China split from taxon 1 about 2.5 MYA (95% highest posterior densities -95% HPD = 1.4-3.7), while taxon 3 diverged from the two taxa approximately 3.4 MYA (95% HPD = 2.3-4.8) (see Suppl. material 2).…”

“…We included 12 new samples from five populations distributed in north and north central Vietnam to another 21 known species' samples of Tylototriton (Table 1). Additionally, five species were selected as outgroups: Echinotriton andersoni, E. chinhaiensis, Lyciasalamandra atifi, Notophthalmus viridescens, and Pleurodeles waltl, to root the tree (Qian et al 2017;Wang et al 2018). .…”

“…A priori criteria for the analysis were set in the program BEAUti v1.8.0. One calibration point, the split between the clade containing Tylototriton vietnamensis + T. panhai and the clade consisting of T. asperrimus and other related species, estimated for 12.4 ± 2.3 million years ago (MYA) (Wang et al 2018), was used to calibrate the phylogeny. A general time-reversible (GTR) model using gamma + invariant sites with four gamma categories was employed along with the assumption of a relaxed molecular clock.…”

“…However, the taxonomic assignments of some populations of T. asperrimus have not been completely resolved. The population from Thuong Tien District, Hoa Binh Province, Vietnam, was identified as T. asperrimus due to low genetic differences in partial mitochondrial (Yuan et al 2011;Nishikawa et al 2013b) and partial nuclear genes (Wang et al 2018) compared with the Chinese population. Nonetheless, other authors regarded this population as an undescribed species, T. cf.…”

“…asperrimus, based Figure 1. Current distribution map of the genus Tylototriton, from South and Central China, to northern Vietnam, Laos, Thailand, Myanmar, India, Bhutan and Nepal (Hernandez 2016;Qian et al 2017;Grismer et al 2018;Wang et al 2018;Grismer et al 2019;Hernandez et al 2019;Zaw et al 2019). In red the distribution areas belonging to the subgenus Tylototriton, and in blue the distribution areas belonging to the sub-genus Yaotriton (Dubois and Raffaëlli 2009).…”