Musk deer (Moschus spp.), the only extant genus of the family Moschidae, consists of seven species and are widely found in forests and mountains in Asia (Yang et al., 2003; Jiang et al., 2020). China has the largest musk deer population and musk source globally (Sun et al., 2018). Six species of genus Moschus are found in China, among which the forest musk deer (FMD, M. berezovskii) and the alpine musk deer (AMD, M. chrysogaster) are the most widely distributed and have the highest wild and captive population (Fan et al., 2018). They inhabit high-altitude coniferous forests or broad-leaved forests (Wang and Harris, 2015), alpine shrub meadow, and mountain forest grassland zone (Harris, 2016) in central and southwestern China, with some overlapping areas. However, wild musk deer populations plummeted to the brink of extinction in the 20th century due to illegal hunting, habitat fragmentation, and other human activities (Wu and Wang, 2006; Cai et al., 2020). The International Union for Conservation of Nature (IUCN) Red List (Wang and Harris, 2015; Harris, 2016) and red list of China’s vertebrates (Jiang et al., 2016) have listed both the species as endangered (EN) and critically endangered (CR), respectively. The captivity breeding of the FMD and AMD began in China in the 1960s to curb the rapid decline of the musk deer population by reducing the pressure on hunting wild musk deer to some extent (Fan et al., 2019). Captive individuals can also serve as a rewilding resource for reintroduction, which is beneficial for effective conservation and population recovery of wild musk deer. However, gastrointestinal diseases occur in the captive FMD and AMD with a fatality rate of about 30%, especially in winter and autumn (Li et al., 2017). Diseases are the most significant constraints on population growth, breeding scale, and musk secretion (Zhao et al., 2011; Zhang et al., 2019).
Gut microbiota has a close mutualistic symbiotic relationship with their hosts during long-term coevolution and is essential in organisms (Nicholson et al., 2012). The complex and variable micro-ecosystem of gut microorganisms were involved in metabolism, immune regulation, intestinal development promotion, pathogen defense, and other physiological activities (Wang et al., 2019; Yoo et al., 2020). Many factors, such as host genetics, diet, season, age, and lifestyle, influence the composition and function of gut microbiota (Zhang et al., 2010; Claesson et al., 2012; O’Toole and Jeffery, 2015). For instance, changes in dietary composition rapidly alter the composition and abundance of gut microbiota (Zmora et al., 2019). Seasonal changes in food composition and availability change the structure and function of gut microbiota in many animals (Amato et al., 2015; Xue et al., 2015). Moreover, captive breeding and ex situ conservation are effective for the conservation of endangered species. Long-term captive breeding has significantly changed the dietary composition of musk deer compared with wild populations (Guo et al., 2019), resulting in changes in the composition and function of gut microbiota (Sun et al., 2020). Therefore, studying the diversity of gut microbiota of endangered species in captivity is essential for assessing the current captive conditions, understanding the appropriate capacity of changes in gut microbiota for their future, and evaluating whether they can be released into the wild. However, the relationship between the diversity, structure, and function of gut microbiota of captive musk deer of different ages and seasonal changes is unclear due to the inadequate relevant data.
In this study, combined with weighted gene co-expression network analysis (WGCNA), the 16S rRNA gene amplicon technology was used for high-throughput sequencing on the Illumina MiSeq sequencing platform to analyze the fecal microbial composition, diversity, and function in captive FMD and AMD in different seasons. This study aimed to (i) explore the composition and differences in the gut microbiota of both musk deer in different seasons; (ii) analyze the core microbiota and its metabolic functions, and their seasonal difference; and (iii) construct a weighed co-occurrence network of gut microbiota for identifying modules of co-occurring taxa and hub OTUs significantly related with the seasonal variation. Therefore, this study can provide a scientific basis for the effective management of captive musk deer.
Figure 5. Identification of key module and hub OTUs based on WGCNA. (A) Correlation between module eigenvalue and traits of musk deer. Depth of color corresponds to depth of correlation and p-value of each module presented in parentheses. (B) Network diagram of the hub OTUs. Each node represented the OTUs whose Ktotal value was in the top 10%, and its color represented the corresponding module. The gray line thickness represents the weight value between nodes (OTUs). (C) Visualization of hub OTUs in black modules. (D) Visualization of full weighted networks in black modules associated with different seasons. The node size represented the Kwithin value of the node in the black module, that is, the size of the connectivity in the module. The gray line thickness represented the weight value between nodes (OTUs). (E) Identification of key OTU in the black module through Cytohubba. The node size represented the Kwithin value, and the shade of red indicated the importance within the module.
This result was published in Frontiers in Microbiology with the title of “Marked Seasonal Variation in Structure and Function of Gut Microbiota in Forest and Alpine Musk Deer”.
The link below will guide you to the reading:
https://doi.org/10.3389/fmicb.2021.699797