Rapid transmission of respiratory infections within but not between mountain gorilla groups

Minimizing disease transmission between humans and wild apes and controlling outbreaks in ape populations is vital to both ape conservation and human health, but information on the transmission of real infections in wild populations is rare. We analyzed respiratory outbreaks in a subpopulation of wild mountain gorillas (Gorilla beringei beringei) between 2004 and 2020. We investigated transmission within groups during 7 outbreaks using social networks based on contact and proximity, and transmission between groups during 15 outbreaks using inter-group encounters, transfers and home range overlap. Patterns of contact and proximity within groups were highly predictable based on gorillas’ age and sex. Disease transmission within groups was rapid with a median estimated basic reproductive number (R0) of 4.18 (min = 1.74, max = 9.42), and transmission was not predicted by the social network. Between groups, encounters and transfers did not appear to have enabled disease transmission and the overlap of groups’ ranges did not predict concurrent outbreaks. Our findings suggest that gorilla social structure, with many strong connections within groups and weak ties between groups, may enable rapid transmission within a group once an infection is present, but limit the transmission of infections between groups.

Development of 79 SNP markers to individually genotype and sex-type endangered mountain gorillas (Gorilla beringei beringei)

The mountain gorilla (Gorilla beringei beringei) is one of two endangered subspecies of eastern gorilla. The principle approach to monitoring the two extant mountain gorilla populations has been to use fecal surveys to obtain DNA profiles for individuals that are then used for capture-recapture-based estimates of abundance. To date, 11 to 14 microsatellites have been used for this purpose. To adapt to ongoing changes in genotyping technologies and to facilitate the analysis of fecal DNA samples by multiple laboratories, we developed a panel of single nucleotide polymorphism (SNP) markers that can be used for future gorilla monitoring. We used published short read data sets for 3 individuals to develop a suite of 79 SNPs, including two sex markers, for a Fluidigm platform. This marker set provided high resolution to differentiate individuals and will facilitate future monitoring, leaving room for additional SNPs to be included in a 96-assay format.

Diet of Grauer’s Gorillas (Gorilla beringei graueri) in a Low-Elevation Forest

Although the vast majority of critically endangered Grauer’s gorillas (<i>Gorilla beringei graueri</i>) inhabit low-elevation rain forests, current insights into this ape’s life history and ecology stem predominantly from 2 small populations ranging in highland habitats. Here, we provide an initial and non-exhaustive overview of food items of Grauer’s gorillas in the Nkuba Conservation Area (NCA), a lower-elevation (500–1,500 m) forest located between Kahuzi-Biega National Park and Maiko National Park in the Democratic Republic of the Congo. Community-based conservation efforts at the NCA aim to protect a population of unhabituated Grauer’s gorillas, which we have studied since 2014. Between 2014 and 2020, we simultaneously tracked 1–3 gorilla groups and recorded a total of 10,514 feeding signs on at least 100 plant species, ants, termites, and fungi. Vegetative plant parts (plant stems, leaves, pith, bark, and roots), especially of Marantaceae and Fabaceae, made up close to 90% of recorded feeding signs, with fruit accounting for most of the remainder and a small (&#x3c;1%) number of feeding signs on invertebrates and fungi. We found that the most frequently recorded food items were consumed year-round, though fruit intake seems to peak in the September-December wet season, possibly reflecting patterns in fruit phenology. The diet of Grauer’s gorillas in the NCA differed from that of Grauer’s gorillas in highland habitat and instead showed similarities with Grauer’s gorillas at the lowland forest of Itebero and with western lowland gorillas (<i>G. gorilla</i>), which live under ecologically comparable conditions.

Daily Travel Distances of Unhabituated Grauer’s Gorillas (Gorilla beringei graueri) in a Low Elevation Forest

To accurately determine the space use of animals, we need to follow animal movements over prolonged periods, which is especially challenging for the critically endangered Grauer’s gorillas (<i>Gorilla beringei graueri</i>) in eastern Democratic Republic of the Congo (DRC). As a consequence, we know little about Grauer’s gorillas, particularly from the lower elevational parts of their range. Between 2016 and 2018, we tracked unhabituated Grauer’s gorillas in lowland forests (500–1,000 m a.s.l.), at the community-managed Nkuba Conservation Area in Nord Kivu (DRC) to provide estimates of daily travel distances (DTD), daily displacement distances (DDD), and the linearity of recorded paths expressed as the Linearity Index (LI): DDD/DTD. We found an average DTD of ∼1.3 km (range 0.05–5.0 km), with temporal variation among monthly averages; specifically, an increase in travel distance over the June–August dry season resulting in peak travel distances at the beginning of the September–December wet season. Daily displacements showed similar temporal variation, which resulted in a lack of obvious temporal patterns in LI. We conclude that the movement patterns of Grauer’s gorillas in lowland forests, which are characterized by larger DTD than those of Grauer’s gorillas that inhabit highland habitats, show similarity to travel distances of other predominantly frugivorous gorillas. Moreover, the observed temporal patterns in space use may be tentatively linked to temporal changes in fruit availability or consumption. These observations have consequences for our understanding of the ecological role that Grauer’s gorillas play and provide baseline data to estimate current and future distributions, abundances, and carrying capacities of this highly threatened animal.