INTRODUCTION
The gut provides a rich and favorable ecological environment for microbial communities, facilitating a complex and dynamic equilibrium among microorganisms. This balance is subject to continuous modifications across different hosts or developmental stages, contributing to a variety of physiological (Hertli & Zimmermann, 2022 ) and pathological processes, including metabolism (Lindsay, Metcalfe & Llewellyn, 2020; Wei et al., 2023 ), nutrient absorption (Flint et al., 2012 ), immune regulation (Siddiqui, Maciver & Khan, 2022; Wei et al., 2023 ), and host ecological behavior (O’Donnell et al., 2020 ). The composition and structure of normal gut microbiota serve as indicators for assessing animal health as well as diagnosing or preventing disease (Hu et al., 2017; Kundu et al., 2017; Rosshart et al., 2017 ). Gut microbes are shaped by a multitude of factors, such as the evolutionary status (Kartzinel et al., 2019 ), feeding habits (Jiang et al., 2017 ), distribution (Qin et al., 2014 ), seasonal variation (Sun et al., 2016; Gao, Yang & Shi, 2023 ), and climate (Greenspan et al., 2020; Li et al., 2020 ). However, the primary determinants affecting the composition of the gut microbiota are the genetic background and dietary habits of the host (Kovacs et al., 2011; Doré & Blottière, 2015 ). Understanding these factors is crucial for studying the ecology and evolution of animal gut microbes.
A variety of factors, including sex, geographical population, breeding status, health condition, local altitude, and temperature, influence the composition and characteristics of gut microbes. For example, significant sex-based differences in microbial community structure have been reported in wild Calotes versicolor , with theBacteroide and Ochrobactrum genera found to be dominant in wild females and males, respectively (Zhang et al., 2022 ). Differences in fecal microbial abundance and gene functional types have also been noted between the Guilin and Xiangyang populations ofPtyas dhumnades (Li, Sun & Xu, 2021 ). Additionally, the relative abundance of Shigella species in fecal samples ofElaphe carinata , noted for its lack of intestinal diseases, is considerably higher than that of two congeneric species, suggesting a potential link to intestinal health (Lu et al., 2019 ). Research has also shown that conditional or potentially pathogenic bacteria are often present in the animal gut microbiota. For example, potential pathogenic bacteria such as Citrobacter , Trichococcus , andErysipelothrix have been detected in the intestines of wildRhabdophis tigrinus (Tang et al., 2019 ) andRhabdophis subminiatu s (Tang et al., 2019 ). Significant differences have also been found in the composition of gut microbiota among populations of Phrynocephalus vlangalii living at different altitudes, with changes corresponding to the altitudinal gradient (Zhang et al., 2018 ). Furthermore, based on semi-natural experiments, Bestion et al . (2017 ) demonstrated that increasing temperature can lead to a decrease in microbial diversity in wild lizards, potentially negatively impacting host survival. Conversely, gut microbiota can be regulated to enhance immune capacity in lizards, thus facilitating adaptation to climate change (Yang et al., 2024 ).
The bamboo pitviper (Viridovipera stejnegeri ) is a common venomous snake with wide distribution across China and Vietnam (David et al., 2001; 2002; Guo et al., 2022 ). It typically inhabits the rocks of streams, grassy and bushy areas, roadsides, vegetable fields, and rock crevices in mountainous areas at elevations ranging from 150 to 2 200 m. These snakes primarily feed on mice, frogs, lizards, and birds (Zhao, 1998; Guo et al., 2022 ). Research by Guo et al . (2016 ) on mitochondrial gene fragments and nuclear genes revealed significant population differentiation within this species.
Snakes, lacking the ability to chew, possess a robust intestinal digestion capacity and remarkably strong hunger tolerance. In the current study, we analyzed the composition, abundance, and carbohydrate-active enzymes (CAZymes) of gut microbes in different populations of V. stejnegeri using metagenomic next-generation sequencing. Our main goal was to compare the gut microbiota in the three different populations and investigate the potential relationship between habitat factors and gut microbes as well as the crucial roles played by gut microbes during carbohydrate metabolism within populations ofV. stejnegeri .