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1. Gut microbiome composition of wild western lowland gorillas is associated with individual age and sex factors

   https://doi.org/10.1002/ajpa.23842  

   Pafčo, Barbora ; Sharma, Ashok K. ; Petrželková, Klára J. ; Vlčková, Klára ; Todd, Angelique ; Yeoman, Carl J. ; Wilson, Brenda A. ; Stumpf, Rebecca ; White, Bryan A. ; Nelson, Karen E. ; et al ( April 2019 , American Journal of Physical Anthropology)

   Environmental and ecological factors, such as geographic range, anthropogenic pressure, group identity, and feeding behavior are known to influence the gastrointestinal microbiomes of great apes. However, the influence of individual host traits such as age and sex, given specific dietary and social constraints, has been less studied. The objective of this investigation was to determine the associations between an individual's age and sex on the diversity and composition of the gut microbiome in wild western lowland gorillas.

   Publicly available 16S rRNA data generated from fecal samples of different groups ofGorilla gorillagorillain the Central African Republic were downloaded and bioinformatically processed. The groups analyzed included habituated, partially habituated and unhabituated gorillas, sampled during low fruit (dry,n = 28) and high fruit (wet,n = 82) seasons. Microbial community analyses (alpha and beta diversity and analyses of discriminant taxa), in tandem with network‐wide approaches, were used to (a) mine for specific age and sex based differences in gut bacterial community composition and to (b) asses for gut community modularity and bacterial taxa with potential functional roles, in the context of seasonal food variation, and social group affiliation.

   Both age and sex significantly influenced gut microbiome diversity and composition in wild western lowland gorillas. However, the largest differences were observed between infants and adults in habituated groups and between adults and immature gorillas within all groups, and across dry and wet seasons. Specifically, although adults always showed greater bacterial richness than infants and immature gorillas, network‐wide analyses showed higher microbial community complexity and modularity in the infant gorilla gut. Sex‐based microbiome differences were not evident among adults, being only detected among immature gorillas.

   The results presented point to a dynamic gut microbiome inGorillaspp., associated with ontogeny and individual development. Of note, the gut microbiomes of breastfeeding infants seemed to reflect early exposure to complex, herbaceous vegetation. Whether increased compositional complexity of the infant gorilla gut microbiome is an adaptive response to an energy‐limited diet and an underdeveloped gut needs to be further tested. Overall, age and sex based gut microbiome differences, as shown here, maybe mainly attributed to access to specific feeding sources, and social interactions between individuals within groups.

    

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2. Comparative life history patterns of female gorillas

   https://doi.org/10.1002/ajpa.24792  

   Robbins, Martha M. ; Akantorana, Moses ; Arinaitwe, Joseph ; Breuer, Thomas ; Manguette, Marie ; McFarlin, Shannon ; Meder, Angela ; Parnell, Richard ; Richardson, Jack L. ; Stephan, Claudia ; et al ( June 2023 , American Journal of Biological Anthropology)

   Several theories have been proposed to explain the impact of ecological conditions on differences in life history variables within and between species. Here we compare female life history parameters of one western lowland gorilla population(Gorilla gorilla gorilla) and two mountain gorilla populations(Gorilla beringei beringei).

   We compared the age of natal dispersal, age of first birth, interbirth interval, and birth rates using long‐term demographic datasets from Mbeli Bai (western gorillas), Bwindi Impenetrable National Park and the Virunga Massif (mountain gorillas).

   The Mbeli western gorillas had the latest age at first birth, longest interbirth interval, and slowest surviving birth rate compared to the Virunga mountain gorillas. Bwindi mountain gorillas were intermediate in their life history patterns.

   These patterns are consistent with differences in feeding ecology across sites. However, it is not possible to determine the evolutionary mechanisms responsible for these differences, whether a consequence of genetic adaptation to fluctuating food supplies (“ecological risk aversion hypothesis”) or phenotypic plasticity in response to the abundance of food (“energy balance hypothesis”). Our results do not seem consistent with the extrinsic mortality risks at each site, but current conditions for mountain gorillas are unlikely to match their evolutionary history. Not all traits fell along the expected fast‐slow continuum, which illustrates that they can vary independently from each other (“modularity model”). Thus, the life history traits of each gorilla population may reflect a complex interplay of multiple ecological influences that are operating through both genetic adaptations and phenotypic plasticity.

    

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3. Long bone diaphyseal shape follows different ontogenetic trajectories in captive and wild gorillas

   https://doi.org/10.1002/ajpa.23636  

   Canington, Stephanie L. ; Sylvester, Adam D. ; Burgess, M. Loring ; Junno, Juho‐Antti ; Ruff, Christopher B. ( August 2018 , American Journal of Physical Anthropology)

   A number of studies have demonstrated the ontogenetic plasticity of long bone diaphyseal structure in response to mechanical loading. Captivity should affect mechanical loading of the limbs, but whether captive apes grow differently than wild apes has been debated. Here, we compare captive and wild juvenile and adultGorillato ascertain whether growth trajectories in cross‐sectional diaphyseal shape are similar in the two environments.

   A sample of young juvenile (n = 4) and adult (n = 10) captiveGorilla gorillagorillaspecimens, with known life histories, were compared with age‐matched wildG.g. gorilla(n = 62) andG. beringei beringei(n = 75) in relative anteroposterior to mediolateral bending strength of the femur, tibia, and humerus. Cross sections were obtained using peripheral quantitative CT.

   Captive and wild adultG.g. gorilladiffered in bending strength ratios for all three bones, but these differences were not present in young juvenileG.g. gorilla. In comparisons across taxa, captive juvenileG.g. gorillawere more similar to wildG.g. gorillathan toG.b. beringei, while captive adultG.g. gorillawere more similar in shape toG.b. beringeiin the hind limb.

   Captive and wildG. gorillafollow different ontogenetic trajectories in long bone diaphyseal shape, corresponding to environmental differences and subsequent modified locomotor behaviors. Differences related to phylogeny are most evident early in development.

    

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4. Fruit‐feeding and activity patterns of mountain gorillas ( Gorilla beringei beringei ) in Bwindi Impenetrable National Park, Uganda

   https://doi.org/10.1002/ajpa.24056  

   Ostrofsky, Kelly R. ; Robbins, Martha M. ( April 2020 , American Journal of Physical Anthropology)

   Availability of fruit is an important factor influencing variation in great ape foraging strategies and activity patterns. This study aims to quantify how frugivory influences activity budgets across age‐sex classes of mountain gorillas in Bwindi Impenetrable National Park, Uganda.

   Daily proportions of fruit‐feeding and activity budgets were calculated using 6 years of observational data on four habituated groups. We fitted generalized linear mixed models to test for age‐sex differences in the amount of fruit‐feeding, and to test whether these factors influence the proportion of time spent feeding, resting, and traveling.

   Bwindi mountain gorillas spent on average 15% of feeding time consuming fruit, with monthly variation ranging from 0 to 70%. Greater amounts of fruit‐feeding were associated with more time feeding and traveling, and less time resting. Immatures tended to spend more feeding time on fruit than adults, but less overall time feeding and more time traveling. There were no significant differences in the amount of fruit‐feeding and overall feeding time between adult females and silverback males, despite differences in body size.

   This study confirms that gorillas are frugivorous, and only the Virunga mountain gorilla population can be characterized as highly folivorous. Along with other frugivorous great apes, Bwindi mountain gorillas alter their activity patterns in response to varying amounts of fruit in their diet. A better understanding of how variable ecological conditions can drive diversity even within a subspecies has important implications for understanding relationships between ecology, body size, and foraging strategies in great apes.

    

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5. Quantifying linear enamel hypoplasia in Virunga Mountain gorillas and other great apes

   https://doi.org/10.1002/ajpa.23436  

   McGrath, Kate ; El‐Zaatari, Sireen ; Guatelli‐Steinberg, Debbie ; Stanton, Margaret A. ; Reid, Donald J. ; Stoinski, Tara S. ; Cranfield, Michael R. ; Mudakikwa, Antoine ; McFarlin, Shannon C. ( February 2018 , American Journal of Physical Anthropology)

   Linear enamel hypoplasia (LEH) is a condition marked by localized reductions in enamel thickness, resulting from growth disruptions during dental development. We use quantitative criteria to characterize the depth of LEH defects and “normal” perikymata in great apes. We test the hypothesis that mountain gorillas have shallow defects compared to other taxa, which may have led to their underestimation in previous studies.

   Previous attempts to characterize LEH morphology quantitatively have been limited in sample size and scope. We generated digital elevation models using optical profilometry (Sensofar PLu Neox) and extracted 2D coordinates using ImageJ to quantify depths in canines from three great ape genera (N = 75 perikymata; 255 defects).

   All defect depths fall outside the distribution of perikymata depths. Mountain gorilla defects are significantly shallower than those of other great ape taxa examined, including western lowland gorillas. Females have significantly deeper defects than males in all taxa. The deepest defect belongs to a wild‐captured zoo gorilla. Virunga mountain gorilla specimens collected by Dian Fossey exhibit deeper defects than those collected recently.

   Shallow defect morphology in mountain gorillas may have led to an underestimation of LEH prevalence in past studies. Defect depth is used as a proxy for insult severity, but depth might be influenced by inter‐ and intra‐specific variation in enamel growth. Future studies should test whether severe insults are associated with deeper defects, as might be the case with Haloko, a wild‐captured gorilla. Ongoing histologic studies incorporating associated behavioral records will test possible factors that underlie differences in defect morphology.

    

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