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