Gut Microbiota and Phytoestrogen-Associated Infertility in Southern White Rhinoceros

Abstract

With recent poaching of southern white rhinoceros (SWR [Ceratotherium simum simum]) reaching record levels, the need for a robust assurance population is urgent. However, the global captive SWR population is not currently self-sustaining due to the reproductive failure of captive-born females. Dietary phytoestrogens have been proposed to play a role in this phenomenon, and recent work has demonstrated a negative relationship between diet estrogenicity and fertility of captive-born female SWR. To further examine this relationship, we compared gut microbial communities, fecal phytoestrogens, and fertility of SWR to those of another rhinoceros species—the greater one-horned rhinoceros (GOHR [Rhinoceros unicornis]), which consumes a similar diet but exhibits high levels of fertility in captivity. Using 16S rRNA amplicon sequencing and mass spectrometry, we identified a species-specific fecal microbiota and three dominant fecal phytoestrogen profiles. These profiles exhibited various levels of estrogenicity when tested in an in vitro estrogen receptor activation assay for both rhinoceros species, with profiles dominated by the microbial metabolite equol stimulating the highest levels of receptor activation. Finally, we found that SWR fertility varies significantly not only with respect to phytoestrogen profile, but also with respect to the abundance of several bacterial taxa and microbially derived phytoestrogen metabolites. Taken together, these data suggest that in addition to species differences in estrogen receptor sensitivity to phytoestrogens, reproductive outcomes may be driven by the gut microbiota’s transformation of dietary phytoestrogens in captive SWR females. IMPORTANCE Southern white rhinoceros (SWR) poaching has reached record levels, and captive infertility has rendered SWR assurance populations no longer self-sustaining. Previous work has identified dietary phytoestrogens as a likely cause of this problem. Here, we investigate the role of gut microbiota in this phenomenon by comparing two rhinoceros species to provide the first characterizations of gut microbiomes for any rhinoceros species. To our knowledge, our approach, combining parallel sequencing, mass spectrometry, and estrogen receptor activation assays, provides insight into the relationship between microbially mediated phytoestrogen metabolism and fertility that is novel for any vertebrate species. With this information, we plan to direct future work aimed at developing strategies to improve captive reproduction in the hope of alleviating their threat of extinction.

Reduced Gut Microbiome Diversity and Metabolome Differences in Rhinoceros Species at Risk for Iron Overload Disorder

“…Previous large wildlife studies that included a few rhinoceros samples demonstrated that host phylogeny and diet influenced bacterial diversity, and the most abundant phyla in most mammals were Firmicutes and Bacteroidetes (Ley et al, 2008; Youngblut et al, 2019). Therefore, the dominance of these two phyla members in the gut microbiota of rhinoceroses across several North American zoos was expected and in accordance with reports of rhinoceros microbiome in China (Bian et al, 2013), Europe (Antwis et al, 2019), San Diego (Williams et al, 2019), South Africa and Texas (Gibson et al, 2019).…”

“…In contrast, the Sumatran rhinoceros metabolome was more closely associated with those of the GOH rhinoceros and white rhinoceros. Williams et al (2019) also reported similar metabolite composition between GOH and white rhinoceroses despite differences in gut microbial composition.…”

“…Most gut microbiome research has focused on rodents and humans, but microbial populations in wildlife, and even horses, are largely uncharacterized much beyond the phyla level (Daly et al, 2001; Ley et al, 2008; Proudman et al, 2015), with the exception of a recent study (Youngblut et al, 2019). A previous paper reported 15–42 and 58–85% unclassified bacteria at the family and genus levels, respectively, across five white rhinoceroses (Bian et al, 2013), and more recent publications on rhinoceros microbiota also reported high proportions of unmapped reads (Gibson et al, 2019; Williams et al, 2019). Similarly, we report 26–52 and 62–78% unclassified reads within family and genus, respectively, across all four rhinoceros species.…”

Endocrine Disruptors in Food: Impact on Gut Microbiota and Metabolic Diseases

“…The effect of soy intake on microbiota composition and diversity has been studied in other animal models, such as porcine models [61,63] and the Southern white rhinoceros [62]. Yeruva et al (2016) [63] determined the influence of diet on the development of the immune system in neonates, using a porcine model.…”

Effects of Phytoestrogens on the Developing Brain, Gut Microbiota, and Risk for Neurobehavioral Disorders

“…A recent study with Southern white rhinoceros (SWR, Ceratotherium simum simum) suggested that dietary phytoestrogens might transform the gut microbiota composition, which may be another mechanism resulting in increased infertility in captive populations fed a diet enriched with such compounds (71). The bacterial profiles of SWR were compared to that of the greater one-horned rhinoceros (GOHR [Rhinoceros unicornis]), who consume a similar phytoestrogen rich diet but show high levels of fertility in captivity.…”