Isolated Grauer's gorilla populations differ in diet and gut microbiome

The animal gut microbiome has been implicated in a number of key biological processes, ranging from digestion to behavior, and has also been suggested to facilitate local adaptation. Yet studies in wild animals rarely compare multiple populations that differ ecologically, which is the level at which local adaptation may occur. Further, few studies simultaneously characterize diet and gut microbiome from the same sample, despite their likely interdependence. Here, we investigate the interplay between diet and gut microbiome in three geographically isolated populations of the critically endangered Grauer's gorilla, which we show to be genetically differentiated. We find population- and social group-specific dietary and gut microbial profiles and co-variation between diet and gut microbiome, despite the presence of core microbial taxa. There was no detectable effect of age, and only marginal effects of sex and genetic relatedness on the microbiome. Diet differed considerably across populations, with the high-altitude population consuming a lower diversity of plants compared to low-altitude populations, consistent with plant availability constraining diet. The observed pattern of covariation between diet and gut microbiome is likely a result of long-term social and environmental factors. Our study suggests that the gut microbiome is sufficiently plastic to support flexible food selection and hence contribute to local adaptation

Opening a can of worms: Population-level transmission of gastrointestinal nematodes among Grauer’s gorilla (Gorilla beringei graueri) social groups.

Poster Session 1 at Ecology & Evolution of Infectious Disease (EEID) 2023 conferenc

The effects of background adaptation and food availability on habitat preference of Corythoichthys flavofasciatus

Habitat preferences are intrinsically linked to factors that facilitate the survival of a species. The relationship between these factors determines how well a species does in its environment. Often habitat choice is related to the availability of food, presence of predators, and proximity to other viable habitats, amongst other variables. How these variables interact depends on fluctuations in the trophic web of which they are a part.Corythoichthys flavofasciatusis a species of pipefish that occurs in the fringing and back reefs of Mo’orea, French Polynesia. It feeds on zooplankton and occurs primarily on dead coral heads that are covered in algal turf. This study aimed to understand the relationship between zooplankton abundance, habitat quality, and substrate types on the habitat preferences of this pipefish. A field survey of the abundance of zooplankton in different habitats was used to determine if more food was available in habitats that were dominated by dead coral. Results suggest that more zooplankton are found above algal turf than live coral. A survey looking at pipefish abundance and amount of coral available in the habitat suggests that pipefish abundance correlates weakly to the amount of algal turf in the environment. An experiment quantifying color change in light and dark morphs of pipefish was conducted to determine if pipefish were capable of background adaptation, depending on substrate color. The results suggest that these observations were not statistically significant but warrant further research, using larger sample sizes. The findings of this study provide insight into the ecological role of pipefish in coral reef habitats

Behavioral variation, parasite transmission, and demography of isolated populations of Grauer's gorilla (Gorilla beringei graueri)

Great apes have long lives, grow slowly, and reproduce late in life. This evolved life-history pattern now threatens many extant populations. Novel anthropogenic threats occur in tandem with ecological and demographic variation, which can have lasting impacts on population growth rates. Grauer’s gorillas (Gorilla beringei graueri) are among the most critically endangered subspecies among the extant great apes but have been relatively understudied. These group-living primates are found in eastern Democratic Republic of the Congo, a region experiencing rapid forest loss resulting in small, isolated gorilla habitats. In this dissertation, I explored three aspects of gorilla biology. In Chapter 1, I studied the effects of seasonal changes in food availability on within-group social interactions. I found that Grauer’s gorillas exhibit group-level changes in how spread out they are when they are foraging compared to when they are resting. However, in line with previous socioecological predictions, gorillas appear to be highly tolerant of group members while foraging, despite seasonal changes in the types of foods they consume. In Chapter 2, I conducted an exploratory analysis of the population-level transmission of nematodes found in Grauer’s gorillas. I used molecular methods commonly employed by parasitologists to identify the diversity of gastrointestinal nematodes found in multiple social groups living in the same habitat. I found that two of the most common taxa exhibited limited population structure, suggesting that gene flow for these nematodes among social groups may be quite high. I also discuss other explanations for this pattern, including parasite life history and development, abiotic factors, host movement, as well as alternative hosts in the habitat. Finally, in Chapter 3, I examined the effects of demographic stochasticity on the growth rate of a small, at-risk gorilla population (with only 2 adult females) in Mount Tshiaberimu, Virunga National Park. I used population viability analysis models to determine how random fluctuations in the number of births and deaths influenced growth rates. I identified the minimum number of female gorillas needed to reinforce the population to limit the effects of demographic stochasticity on the likelihood of extinction. The results of these studies offer insight into the natural history and ecology of Grauer’s gorillas. This work can help us understand how small, threatened populations are adapting to a rapidly changing landscape, which can improve conservation outcomes for this charismatic primate

Viability analysis for population reinforcement of Grauer's gorillas at Mount Tshiaberimu, Democratic Republic of Congo

Reintroduction and translocation programs have been sparingly used for the management of endangered primate populations. Mount Tshiaberimu in eastern Democratic Republic of the Congo (DRC) contains 6 Grauer's gorillas (Gorilla beringei graueri) with only 2 adult females. Without intervention, this population is at high risk of extinction. We designed population viability analysis models to compare different release scenarios of wild-born captive female gorillas housed at the Gorilla Rehabilitation and Conservation Education (GRACE) Center in the DRC. We identified the minimum number of females needed to maintain a viable population in this habitat. We used a stochastic Leslie matrix model and a more complex individual-based model to project population growth. We used published demographic parameters for mountain gorillas (Gorilla b. beringei) corresponding to a 3.2% annual growth rate, and then applied a correction factor to female fertility to obtain parameters consistent with 1% and 2% growth rates. We ran each scenario over a 50-year time period (1,000 simulations) to determine the final population size and risk of local extinction. Results from our optimistic (3.2% growth) and conservative (1% growth) individual-based model projections indicated that the extinction risk dropped below 1% with the release of at least 2 or 3 females, respectively. Both approaches predicted similar extinction risks for all scenarios; however, the variance in final population size was higher with the individual-based model. For long-lived mammals like primates, we recommend the use of individual-based models, which can incorporate life-history parameters such as long gestation and nursing periods. Our analysis suggests a translocation of ≥3 females to rescue the Tshiaberimu gorilla population in the short term. Factors such as inbreeding depression, habitat quality, disease risks, and anthropogenic pressures will need to be evaluated in later stages of population reinforcement planning

Viability analysis for population reinforcement of Grauer's gorillas at Mount Tshiaberimu, Democratic Republic of Congo

Reintroduction and translocation programs have been sparingly used for the management of endangered primate populations. Mount Tshiaberimu in eastern Democratic Republic of the Congo (DRC) contains 6 Grauer's gorillas (Gorilla beringei graueri) with only 2 adult females. Without intervention, this population is at high risk of extinction. We designed population viability analysis models to compare different release scenarios of wild-born captive female gorillas housed at the Gorilla Rehabilitation and Conservation Education (GRACE) Center in the DRC. We identified the minimum number of females needed to maintain a viable population in this habitat. We used a stochastic Leslie matrix model and a more complex individual-based model to project population growth. We used published demographic parameters for mountain gorillas (Gorilla b. beringei) corresponding to a 3.2% annual growth rate, and then applied a correction factor to female fertility to obtain parameters consistent with 1% and 2% growth rates. We ran each scenario over a 50-year time period (1,000 simulations) to determine the final population size and risk of local extinction. Results from our optimistic (3.2% growth) and conservative (1% growth) individual-based model projections indicated that the extinction risk dropped below 1% with the release of at least 2 or 3 females, respectively. Both approaches predicted similar extinction risks for all scenarios; however, the variance in final population size was higher with the individual-based model. For long-lived mammals like primates, we recommend the use of individual-based models, which can incorporate life-history parameters such as long gestation and nursing periods. Our analysis suggests a translocation of ≥3 females to rescue the Tshiaberimu gorilla population in the short term. Factors such as inbreeding depression, habitat quality, disease risks, and anthropogenic pressures will need to be evaluated in later stages of population reinforcement planning