Currently, most niche studies are built at the species level, treating species as individual, undifferentiated entities in response to climate change. Some studies believe that the niches at the species level are conservative, and other studies have shown that the niches of species have diverged. Species are a collection of evolutionary lineages that differ in time of differentiation, evolutionary independence, and genetic specificity. For widely distributed species with systematic geographic structures, it is difficult to accurately describe the evolutionary dynamics of ecological niches between different genetic clades adapted to different climatic conditions using ecological niche models (ENMs) of integrated lineages at the species level. In addition, the morphological evolution and phenotypic plasticity of different clades under intraspecific niche dynamics need to be observed.
The Tibetan Plateau continues to rise northward under the influence of the collision of the Indian Ocean plate and the Asian plate, resulting in intricate alpine valleys and violent climatic fluctuations in the mountains around the Tibetan Plateau, which provide diversified ecological opportunities for the differentiation of intra-species branches and the evolution of ecological niches. The Tibetan toothed toad is distributed in the southeastern edge of the Qinghai-Tibet Plateau, spanning adjacent mountain systems such as the Himalayas, the Qinghai-Tibet Plateau, Hengduan Mountain and Minshan Mountains, and is distributed at altitudes from 2400m to 5270m, so the widely distributed species provide good research materials for studying the evolution of ecological niches and morphological evolution within intraspecies.
The team led by Jiang Jianping and Xie Feng, researchers of the Amphibian and Reptile Diversity and Conservation Project Group of the Chengdu Institute of Biology, Chinese Academy of Sciences, and capital normal university, based on biological data sampled for many years of scientific research, combined with world climate data (WorldClim database), using ecological niche models (ENMs) and environment principal component analyses, PCA-env), phylogenetic comparative methods (PCMs), and phylogenetic generalized least squares (PGLS), explored the level of ecological niche differentiation between the branches of the Tibetan dendritic toad, the specific forms of ecological niche differentiation, Niche differentiation contributes the most to climatic factors as well as the response to morphological evolution.
The results showed that the mitochondrial genome was genetically differentiated into 6 branches, of which 3 were (branch E. A, E.B and E. C) Significant niche differentiation occurred (based on ENMs and PCA-env methods: Schoener's D is less than the expected Schoener's D value under the null hypothesis, and the bidirectional niche similarity test P < .05, the null hypothesis is rejected, i.e., the niche differentiation occurs). In this case, niche differentiation is mainly caused by niche expansion rather than niche filling (niche expansion: metastatic niche vs. local niche E > U; niche filling: metastatic niche vs. local niche U > E, see table 3). Environmental principal components PC3 (composed mainly of BIO2 and BIO3), PC4 and PC5 (mainly composed of BIO6 and BIO7) dimension environmental factors follow Brownian motion along phylogenetic relationships to promote the evolution of ecological niches, a conclusion that is almost consistent with the environmental factors that promote the evolution of head body growth. Moreover, niche differentiation due to niche expansion does accompany morphological evolution (e.g., head body length (SVL) with strong phylogenetic signals) and the occurrence of phenotypic plasticity (e.g., forearm and hand length (LAHL), full leg length (HLL), and foot length (FL)). This study provides a research model and theoretical framework for the evolution of ecological niches and morphological characteristics of inter-species within the species of widely distributed species.
The research was published in Ecology and Evolution under the title of Climatic-niche evolution with key morphological innovations across clades within Scutiger boulengeri (Anura: Megophryidae). The research work was funded by the Second Comprehensive Scientific Expedition to the Tibetan Plateau, the Biodiversity Survey and Assessment Project of the Ministry of Ecology and Environment, the Construction of the Basic Conditions Platform of the Sichuan Provincial Department of Science and Technology, and the China Biodiversity Observation Network.
Figure 1. Distribution map of occurrence sites of each branch
Figure 2.(a) Lineage relationships and geographical extents obtained based on the minimal convex shape method; (b) suitable distribution areas for each clade; (c) ancestral relationship reconstruction along climatic principal components (PCs) and elevations
Figure 3.(a) 3D-PCA of environmental variables; (b) ecological niche distribution of bio3 along the climatic variable of each branch; (c) correlation and principal component contribution of each factor involved in PCA-env analysis; (d-e) ecological niche equivalence test results; (f-g) ecological niche similarity bidirectional test results; (h-i) ecological niche dynamic analysis results, red represents the expansion ecological niche, green represents the stable ecological niche, and blue represents the overlapping area of the expanded ecological niche and stable ecological niche
Source: Chengdu Institute of Biology, Chinese Academy of Sciences