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Understanding the intrinsic driving mechanisms of biodiversity formation from a microevolutionary perspective is one of
the important scientific questions of conservation genetics.
Among them, the evaluation of the genetic structure and population history dynamics of the target species, and the analysis of the hybridization suitability of the hybridization zone are the major difficulties in the research of this discipline
.
How to properly distinguish population differentiation, and even whether speciation is the result of nuclear site hybridization or environmental selection, is still one of
the challenges that the discipline needs to face.
In recent years, with the rise and development of gene flow detection models based on consistency theory, the internal and external mechanisms of speciation can be explored by integrating time-corrected phylogenetic relationships, ecoclimatic factors, morphological data and various statistical methods, which can better provide new perspectives and ideas
for biodiversity conservation.
The team led by Xie Feng, a researcher at the Chengdu Institute of Biology, Chinese Academy of Sciences, took the unique Tibetan toothed toad (Scutiger boulengeri) in the mountain streams of the Qinghai-Tibet Plateau as a model, and analyzed the mitochondrial and nuclear gene genetic structure of the toad through detailed field investigations, molecular experimental data and literature in the past three years, based on consistency theory ( Approximate Bayesian models (DIYABC and Migration-N) under Coalescent theory evaluate population history dynamics based on nuclear genes, using geographic cline The location of the hybrid zone was analyzed, and information such as climatic factors and head body length of the toad distribution area was integrated using a variety of statistical methods (multiple matrix regression with randomization, partial Mantel tests and Mantel tests) further evaluated the inducers of this chaotic group structure
.
The results showed that there were significant nucleoplasmic inconsistencies
in the genetic structure of this species.
From the phylogenetic analysis of mitochondrial genes, it was found that the toad coexisted in eight small branches and was classified into three deeply differentiated genetic clades, with obvious geographical structure (Fig.
1A).
； Analysis of the genetic structure of nuclear genes revealed that there were three completely different population structures in the toad species, and there was high-frequency gene flow between the populations, and there was no obvious geographical structure (Figures 2A and 2B).
Approximate Bayesian models (DIYABC and Migration-N) analysis based on Coalescent theory show that intraspecific population structural differentiation is caused by the geographical isolation of ancestral groups (Early Pleistocene, about 2.
49 Ma) Some individuals of the two groups that initially differentiated after the initial differentiation underwent secondary contact and interbred due to climate fluctuations (Holocene, about 0.
59 Ma A third group of offspring is produced, which is accompanied by changes in population size (Figure 3A).
The ratio of the mitochondrial gene genetic differentiation index (F ST) to the nuclear gene F ST is 2.
3, No androgenic spread
was detected.
Geographic cline analysis showed that the toad established a wide hybridization zone (gradient width) in southwest China (near Hengduan Mountain).
277.
63 km, Figure 3B), with significant cross-infusion between populations and no significant reproductive isolation, suggesting that the hybrid may have a high suitability
.
In addition, the results showed that mitochondrial genes (mtDNA) exhibited as geographic isolation by distance (IBD) (Figure 4A), while nuclear genes (nuDNA) Manifested by Isolation by environment (IBE) (Figures 4B and 4C), the mitochondria - Inconsistent nuclear gene differentiation speculates that population differentiation is first caused by geographic isolation, and then rainfall-mediated hybridization produces a wide hybridization zone, which leads to the more confusing geographical structure
of the nucleus of the Tibetan tooth toad.
The study revealed the complex population history of the Tibetan tooth toad, which was facilitated by specific climatic factors that facilitated gene flow within the system, ultimately leading to the species-specific inheritance pattern
.
Figure 1 Time-calibrated phylogenetic tree and sampling point distribution plot based on mitochondrial DNA (Figure 1).
Figure 2 Analysis of geographical distribution and genetic structure (Figure 2).
Figure 3 Optimal population historical dynamic model and geographic gradient analysis (Figure 6.
).
Figure 4.
Mantel test analysis (Figure 7).
The study is entitled "A wide hybrid zone mediated by precipitation contributed to confused geographical structure of Scutiger boulengeri" and published online in an internationally renowned journal Zoological Research
。 Lin Xiuqin, a doctoral student at the Chengdu Institute of Biology, Chinese Academy of Sciences, is the first author of the paper, and researcher Xie Feng is the corresponding author
.
Researcher Jiang Jianping, researcher Yang Weizhao, and Professor Shi Zonggang of Capital Normal University participated in the research
.
The study was supported by the Second Comprehensive Scientific Expedition to the Qinghai-Tibet Plateau (STEP, 2019QZKK05010503), the Biodiversity Investigation and Assessment Project of the Ministry of Ecology and Environment (2019HJ2096001006), and the Construction of the Basic Conditions Platform of the Department of Science and Technology of Sichuan Province (2019JDPT0020 ) and funded
by projects such as the China Biodiversity Observation Network (Sino BON).
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