Investigations into the gut microbiome of wild populations are considered an emerging priority for assessing the health of these populations in the face of ever-increasing anthropogenic disturbances (West et al., 2019). Identifying potential endogenous and exogenous factors that might play a role in shaping the microbiome is paramount, especially when considering the effect of microbiota on an animal’s health status and the possible implications for the conservation and management of endangered species (Bahrndorff et al., 2016; Jiménez and Sommer, 2016). In this context, we analysed the gut microbiome of 53 muriqui individuals from the Caparaó National Park, Brazil. We aimed to provide an initial assessment of this critically endangered species’ microbiome and in particular, to investigate the putative effect of group distribution (i.e., geographical location) and host genetics on their microbial structure and composition.
Overall, we observed that Bacteroidetes was the predominant phyla followed by Firmicutes, with the dominant classes represented by Bacteroidia and Clostridia, with both phyla and classes being commonly found in primate guts (Clayton et al. 2018, Nagpal et al. 2018, Yao et al., 2021, Zhao et al., 2023). Amongst the individuals analysed, 7.40% (n = 4, MC10, MC104, MC112 and MC41) showed differences in their bacterial community composition, with the abundance of phylum Proteobacteria (class Gammaproteobacteria) accounting for > 20% of the total reads. Overgrowth of Proteobacteria, which include numerous pathogenic genera of bacteria, has been suggested as a signature of dysbiosis and disease in humans, including metabolic disorders, inflammation, and cancer (Shin et al., 2015, Rizzatti et al., 2017). This compositional shift might reflect host or environmental changes that could lead to dysbiotic gut microbiomes or natural variations in the group such as different feeding strategies (Mallott et al., 2018), the age of the individuals (Reveles et al., 2019), reproductive state (Sun et al., 2020), or social status (Rudolph et al., 2022) for example. A comparison of the three social groups showed the presence of Actinobacteria only in individuals inhabiting Vale do Aleixo. Actinobacteria, even though usually found in low abundance, has a major role in maintaining gut homeostasis (Binda et al., 2018, Sakarkar, 2022).
Two out of the four individuals (MC104 and MC112) had the lowest alpha diversity values recovered among the analysed groups (MC104/MC112 – Observed = 40/88, Chao1 = 40/92.5, Shannon = 2.17/2.63, Simpson = 0.78/0.88). Low alpha diversity has been previously detected together with dysbiosis of the gut microbiome for captive primates and linked to dietary changes and increased stress levels (McKenzie et al, 2017, Frankel et al., 2019). However, dysbiosis remains poorly reported for wild primates (and indeed, most wild species) and further investigations are required to understand patterns in wildlife populations more generally (Ghosh et al., 2021). Dietary changes could also be linked to compositional shifts found for the other two individuals showing higher bacterial diversity (MC10 and MC41). Similar compositional shifts between Bacteroidetes and Proteobacteria have been previously reported and linked to distinct food intakes for the Arunachal macaque, with a high prevalence of Bacteroidetes in animals who foraged upon cultivated crops in contrast to an enriched Proteobacteria for groups feeding on human leftover food remains (Ghosh et al., 2021).
A predominantly folivorous and frugivorous diet is known for muriquis. Studies assessing the muriqui’s diet showed a diet composition including resources such as leaves, fruits, flowers, and additional items (e.g., twigs, tree barks, stem) (Carvalho-Jr et al., 2004). Knowledge in feeding behaviour remains limited for Brachyteles, especially for the Northern muriqui. However, variation in the percentage of feeding records was previously recorded for groups inhabiting distinct areas (i.e., higher intake of lowers in Fazenda Esmeralda than in Estação Biológica de Caratinga which had a comparatively higher proportion of fruit consumption; Rímoli and Ades, 1997, Carvalho-Jr et al., 2004), and shifts towards a more folivorous diet when fruits are scarce were reported and linked possibly to changes in rainfall and food resource availability (Strier, 1991). Yet, the diet of muriquis inhabiting the CNP and possible diet shifts remains largely unknown to date.
Although no significant difference was found for the alpha diversity measures recovered among the analysed groups, the overall values were lower than reported for other primates of the Atelidae family (McKenzie et al., 2017, West et al., 2019). In this study, the muriqui showed Shannon bacterial diversity ranging from 3.93 to 4.41, whereas for both Alouatta spp. and Ateles spp. with values above 6 recovered for wild individuals and values above 4 were retrieved for individuals in captivity (McKenzie et al., 2017). Still, a lowered bacterial diversity has been observed in primates living in captivity or fragmented areas (Amato et al., 2013; Barelli et al., 2020, Trosvik et al., 2018, Zhao et al., 2023) and the small group sizes inhabiting this forest remnant might have contributed to this reduction in gut microbial diversity. It is important to note, however, that the alpha diversity values herein retrieved were in line with results obtained by Harrison et al. (2021), in which values < 4 (Shannon diversity) were retrieved for muriqui, with this species showing a more diverse microbial community when compared to other mammal species (e.g., capuchin monkey, eastern black rhino). Therefore, a more in-depth comparative analysis of wild primate bacterial diversity, alongside an investigation of the underlying factors responsible for shaping microbiome diversity, is needed.
Although no significant differences in microbial community composition were found across analysed groups, a differential abundance was recovered for some of these groups. The highest amount of over-represented taxa was seen in the VFP group, including the families Ruminococcaceae, Erysipelotrichaceae, Muribaculaceae, Atopobiaceae, Prevotellaceae and Lachnospiraceae which included 2 ASVs belonging to Shuttleworthia. In contrast to that, the VSM groups had only one over-represented ASV with Staphylococcus being detected in a significantly greater amount when contrasted to the other two groups. In the VA group, only Mycoplasma showed a significantly greater abundance in comparison with the VFP and VSM groups, with several taxa underrepresented in this group when compared to the remaining ones. Taxa showing a lower abundance in VA included the families Atopobiaceae, Eggerthellaceae, Prevotellaceae, Ruminococcaceae and the genera Selenomonas and Dialister. Across these families, several taxa have been previously linked to gut health such as playing an important role in plant secondary compound metabolism (e.g., Eggerthellaceae, Greene et al., 2020), acting in the production of butyrate and other short-chain fatty acids (previously associated to neuro-immunoendocrine regulation) through bacterial fermentation of dietary fibres (e.g., Ruminococcaceae, Silva et al., 2020), and playing a role in host lipid metabolism or inflammatory diseases (e.g., Erysipelotrichaceae, Kaakoush, 2015). These taxa were highly abundant in VFP individuals in contrast to the other groups. Staphylococcus, the only genus differentially abundant in the VSM group comprises over 40 species, including the pathogenic S. aureus which has recently been of concern due to its putative zoonotic transmission and impact on wildlife health (Tang et a., 2021). In this case, more accurate identification is paramount to understanding the impact of a greater abundance of this genus/species on the investigated social group. In regard to the VA group, the highly abundant Mycoplasma represent a commensal group of bacteria widely detected in association with the mucous membrane of mammals, however, the occurrence of potential opportunistic infections associated with this bacteria has been previously reported including Neotropical primates (e.g., detection of Mycoplasma sp. in an Alouatta caraya individual showing normochromic and macrocytic anaemia, Bonato et al., 2015). Besides that, this group also had an underrepresentation of Selenomonas and Dialister, with the first including species associated with fibre digestion in ruminants and/or fermentation of lactate and soluble sugars (Sawanon et al., 2011, Hespell et al., 2006). The latter, Dialister, a lactic acid and fermentative bacteria, shows a lower abundance in wild colobine primates when compared to captive individuals, with decreased levels being further associated with lower levels of social integration and increased dysbiosis (Amato et al., 2016, Garber et al., 2019, Pinacho-Guendulain et al., 2022). These differential abundances could provide some insights in regards to animals' gut health and/or the effect of environmental conditions, including food availability and foraging behaviour. On that account, a more detailed functional analysis of bacterial communities including metagenomic analysis and metabolomic profiling is key.
The gut microbiome itself is shaped not only by extrinsic conditions (i.e., diet, lifestyle, habitat heterogeneity) but also by intrinsic factors (i.e., sex, age, genotype) (Amato et al, 2013, Bahrndorff et al., 2016, Dubois et al., 2017; Wasimuddin et al., 2017). In this context, the host microbiome has a two-way route, both influencing the host’s immune system and being influenced by the host's genetic diversity (Montero et al., 2021). The association between genetic differences among hosts and in shaping their susceptibility to pathogens is well known. Yet, the contribution of host genes to the microbiome remains mostly unclear (Tabrett and Horton, 2020).
Considering the role of geography in shaping the gut microbiome has not been seen herein at this microgeographic scale, an investigation of the correlation between host genetics and microbiome diversity and composition was performed. In this study, 14 nuclear microsatellite loci were used to investigate the association between the genetic makeup and gut bacterial communities of the host. No effect of muriqui genetic diversity on microbial diversity was obtained, as demonstrated by the absence of a correlation between individual heterozygosity (Ho – observed heterozygosity, HL – homozygosity by loci) and bacterial ASV richness (Observed, Chao1, Shannon, Simpson, all p = > 0.05). However, the influence of host genetics on microbiome was demonstrated through a significant positive correlation retrieved between beta diversity indices and genetic distances (Mantel test, p < 0.05), with the highest r value retrieved for the Weighted UniFrac distance, highlighting the importance of considering taxa abundance and phylogenetic relationships. These results demonstrate that microbial community structure may be influenced by genetic relatedness, as previously reported by Grieneisen et al. (2021) where a high gut microbiome heritability was demonstrated after analysing 16,000 baboon gut microbiome profiles obtained for 585 individuals during a 14-year-long study.
The results obtained herein offer an interesting insight into the Northern muriqui’s management and conservation. The demonstrated influence of host genetics on the microbiome and the absence of geographic filtering (no difference retrieved between analysed social groups) might indicate a possible flow of individuals between these groups. Female muriquis are known to emigrate from their natal groups, a rare life history strategy amongst primates (Strier et al., 2015). This dispersal pattern could help explain the similarities found amongst the analysed groups due to genetic and microbiota exchange, thus, indicating the possible dispersal of females between groups despite the geographical barriers (i.e., a mountain chain splitting the area into two sides - western and eastern; Fig. 1).
Anthropogenic disturbances are known to heavily impact wildlife populations in a plethora of forms, including changes in host microbiomes (Zhu et al., 2021). Disruptions in the gut microbiome composition have been demonstrated, including the domestication and ‘humanization’ of the wildlife gut microbiome (Dillard et al., 2022; Prabhu et al., 2020), and the shift in the microbiota community composition due to an increase in disease-associated taxa and a decrease of beneficial bacteria (Wasimuddin et al., 2022). On top of that, population bottlenecks lead to the loss of genetic variation, increased inbreeding and therefore, resulting in a less diverse microbiome. The constrained microbiome diversity must be the focus of discussion, alongside population size and genetic diversity, when dealing with threatened populations, as it may play a significant role in host fitness and adaptability (Ørsted et al., 2022). Species reintroductions/translocations represent one of the key effective strategies deployed towards the conservation of threatened species with reduced population sizes (Zhul et al., 2021). Despite the efforts made in implementing ex-situ programmes mimicking natural conditions, captive animals are often kept under various conditions that might greatly differ from their natural environments. In this context, investigating their wildlife microbiome is paramount to provide subsidies for comparisons with animals kept in captivity before the start of release programmes, especially considering the role of microbiota in nutrition uptaking and general host health.