INTRODUCTION
Gut microbiota (GM) play beneficial roles in the homeostasis and immune systems of hosts in addition to improving their general health and nutritional status (Claesson et al 2012, Round and Mazmanian 2009, Sommer and Backhed 2013). Consequently, changes in the composition, diversity, or abundance of GM are frequently associated with diseases and immune system problems (Evans et al 2013, Zhernakova et al 2016). In addition, a considerable body of research over the past decade has revealed that host diet, stressors, and biogeography are major factors that affect GM dynamics (Knight and Girling 2003, Versalovic and Relman 2006).
Giant pandas (Ailuropoda melanoleuca ) are endemic to China, but exhibit rare wild populations due to decreasing population sizes (Shengzhi et al 2018, Zhang et al 2018). They are well known for their unique diet comprising bamboo, despite that they belong to the order Carnivora and possesses a typical carnivorous digestive system (Wei et al 2015, Zhu et al 2011). Interestingly, the giant panda has not evolved any enzymes specific for cellulose digestion, despite their unique dietary adaptation (Hu et al 2017). Therefore, it is not known how giant pandas rely on high fiber diets characterized by low-nutritional components. It has consequently been hypothesized that giant pandas rely on symbiotic gut microbial populations to degrade nutritional components of their highly fibrous diets including cellulose, hemicelluloses, and lignin, which are all key components of their bamboo diets (Hu et al 2017). Despite the investigation of this hypothesis by multiple studies (Zhu et al 2011), it has remained unresolved (Wei et al 2018). Nevertheless, it is clear that the GM of giant pandas play roles in their dietary metabolisms, although the extent of these roles may be unclear.
Giant panda cubs also exhibit unique dietary conversion phases, changing from milk to bamboo diets during development. Significant shifts in the compositions of GM concomitantly occur in giant panda infants during the transition to more solid and varied diets (Sghir et al 2000). Accordingly, investigating GM variation within giant pandas during dietary shifts may provide evidence for the mechanisms underlying the dietary specialization of giant pandas. Indeed, several studies have compared the GM of milk- and bamboo-fed giant pandas (Guo et al 2018, Zhang et al 2018). However, diet was not the only unique variable in the comparison groups of these studies, and it is thus difficult to infer the influences of diet on the GM of giant pandas from these studies.
The reintroduction of captive giant pandas effective at increasing their wild population sizes and mitigating population declines. The reintroduction of extirpated or threatened species is a remedial measure that can generally prevent species extinctions, and has been used in conservation efforts for wolves (Smith et al 2000) and giant tortoises (Gibbs et al 2010). Remarkable achievements have been made in the giant panda conservation breeding program (e.g., through mating, artificial insemination, and parental care behaviors), contributing to the sustainment and increase of giant panda populations that can then be used in reintroduction efforts to supplement wild populations (Li et al 2017, Wei et al 2015, Zhang et al 2004). As indicated above, human-associated microbial communities can be quickly and profoundly altered by typical human activities and ecological backgrounds (David et al 2014). Likewise, accumulating evidence has emphasized that gastrointestinal disease is a primary cause of giant panda deaths (Tun et al 2014), indicating that their gut microbial communities play crucial roles in improving reintroduction success rates. However, studies of giant pandas have only compared GM compositions between captive and wild giant pandas, while few have evaluated the GM characteristics of pandas with different lifestyles (Wei et al 2015, Wu et al 2017, Zhu et al 2011). Moreover, these studies have investigated samples of captive and wild giant pandas from different individuals, although individual microbiota differences are a significant confounding factor when comparing community structures (Xue et al 2015). Thus, little is known regarding the impact of lifestyle variation on the GM of giant pandas. Consequently, the aims of this study were to evaluate the influence of dietary and lifestyle changes on the diversity and composition of giant panda gut microbial communities in order to understand the interactions among the host and their GM and inform future conservation efforts.
MATERIALS AND METHODS