Rare gut microbiota associated with breeding success, hormone metabolites and ovarian cycle phase in the critically endangered eastern black rhino

Abstract

Background: Host microbiomes play a role in hormone production and subsequent fertility in humans, but this is less well understood in non-model organisms. This is of particular relevance to species in zoo-based conservation breeding programmes, as relationships between host microbiome composition and reproductive output may allow for the development of microbial augmentation strategies to improve success. Here, we characterise faecal bacterial communities of breeding and non-breeding eastern black rhino (Diceros bicornis michaeli) using 16S rRNA gene amplicon sequencing and quantify progestagen and glucocorticoid metabolite concentrations through enzyme immunoassays to identify such relationships.

Results: We identified significant differences in black rhino gut microbiome composition according to ID, institution, breeding success and ovarian cycle phase. In particular, the gut microbiome during pregnancy and post-parturition was significantly altered. Around a third of bacterial genera showed more than ± 10% correlation with either progestagen and/or glucocorticoid concentration, and in general, microbial genera correlated with both hormones in the same direction. Through a combination of analyses, we identified four genera (Aerococcaceae, Atopostipes, Carnobacteriaceae and Solobacterium) that were significantly associated with breeding success, pregnancy and/or post-parturition, and higher faecal progestagen metabolite concentrations. These genera had a lower-than-average relative abundance in the gut microbiome.

Conclusion: Our results indicate that many members of the gut microbiome of black rhino are associated with hormone production and breeding success, and some members of the rare microbiota appear to be particularly important. Although the directionality of the relationship is unclear, the variation in gut microbiome communities represents a potential biomarker of reproductive health. We identified four genera that were associated with multiple indicators of reproductive output; these could be candidate probiotics to improve the breeding success of black rhino in zoo-based conservation breeding programmes. Further work is required to understand the efficacy and feasibility of this, either directly through microbial augmentation (e.g. probiotics) or indirectly via dietary manipulation or prebiotics.

Keywords: Conservation breeding programmes; Faecal metabolites; Glucocorticoids; Indicator analysis; Progestagens.

Fig. 1

NMDS plots of rhino microbiomes plotted according to a ID, b institution, c reproductive success and d cycle phase. Smaller dots indicate individual samples and larger filled circles indicate group centroids

Fig. 2

Relative abundance of bacterial phyla association with black rhino according to a institution, b reproductive success and c cycle phase

Fig. 3

Relationship between log faecal progestagen and log faecal glucocorticoid metabolite concentrations according to the two cycle phases, pregnancy, and post-parturition

Fig. 4

Heatmap showing correlation coefficient between relative abundance of bacterial genera and faecal hormone metabolite measures. Only genera with coefficient > ± 0.10 for one or both hormones are shown (a blank tile indicates this genus did not have a prevalence of > ± 0.10 for a given hormone)