Are the gorillas in Bwindi Impenetrable National Park “true” mountain gorillas?

The gorillas that inhabit Bwindi Impenetrable National Park in Uganda are the least known of the eastern gorillas. Because they are an allopatric population living a minimum of 25 km from the well‐studied population of mountain gorillas (Gorilla beringei beringei) in Rwanda and have certain morphological and ecological differences from these gorillas, their taxonomic status has been in question in recent years. This study presents new craniodental metrics from Bwindi individuals and compares them to Virunga individuals as well as to eastern lowland gorillas, G. gorilla graueri. Multivariate statistics, including MANCOVA, least‐squares, regression, and principal components analyses, were used to evaluate how closely the Bwindi crania resemble the Virunga crania and how both relate to G. g. graueri. Results indicate that the Bwindi gorillas have generally smaller crania than the Virunga gorillas, but when metrics are log‐transformed, the only variable that distinguishes the Bwindi individuals is a longer face. When both populations are compared to G. g. graueri, they cluster together separately from the eastern lowland gorillas, sharing such features as higher rami, wider bigonia, longer mandibles, and wider and shorter mandibular symphyses in relation to G. g. graueri. Functional morphological explanations for these differences are discussed, but lacking measurements of the physical properties of G. g. graueri, they cannot fully be explained. Results clearly indicate that at least pertaining to the cranium, upon which most gorilla taxonomy is based, the Bwindi gorillas are proper mountain gorillas (G. b. beringei). Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

A Preliminary Study of the Temporal and Spatial Biomass Patterns of Herbaceous Vegetation Consumed by Mountain Gorillas in an Afromontane Rain Forest

Although many animal species consume herbaceous vegetation found in African tropical forests, little is known of the temporal and spatial availability of these plants. From September 2004 to August 2005 we conducted a study that quantified the temporal and spatial biomass availability of 20 species of herbs frequently consumed by endangered mountain gorillas at two locations (Buhoma and Ruhija) in Bwindi Impenetrable National Park, Uganda. In general, the biomass of herbs varied over the study period, but these changes were relatively small. For 12 of 18 and nine of 11 species in Buhoma and Ruhija, respectively, herb biomass differed significantly among habitat types. Of the nine species found in both locations, seven species had a higher biomass at Ruhija, one species had a higher biomass at Buhoma, and one species showed no difference. These results demonstrate that herb biomass varied little temporally but spatial differences in herb biomass were more pronounced. Future studies should investigate the variables that may influence herb phenological patterns such as rainfall, light, soil quality, previous disturbance regimes, and animal foraging and trampling damage.     

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

Objectives

The approximately 250 years old remains of the Kwäd?y Dän Ts'ìnch? man were found in a glacier in Canada. Studying the state of preservation of the corpse, we observed black deposits in his lung. Following this observation we wanted to determine: (1) location of the deposits in the lung tissue, (2) composition and origins of the deposits.

Methods

By light microscopy (LM) and transmission electron microscopy (TEM), we studied the deposits in the Kwäd?y Dän Ts'ìnch? man’ s lung and compared it with distribution of anthracotic deposits in contemporary samples from the David Harwick Pathology Centre (DHPC). To determine chemical composition of the inclusions we used Raman spectroscopy. Scanning electron microscopy and elemental mapping was used for determine the chemical elements.

Results

The histopathological identification of anthracosis in the Kwäd?y Dän Ts'ìnch? man's lung allowed us to distinguish crushed parenchyma from conducting airway tissue and identification of particles using LM and TEM. Crystal particles were found using TEM. Ordered carbonaceous material (graphene and graphite), disordered carbonaceous material (soot) and what might be minerals (likely conglomerates) were found with Raman spectrometry. Gold and lead particles in the lung were discovered with scanning electron microscopy and elemental mapping.

Conclusions

Presence of soot particles in anthracotic areas in the Kwäd?y Dän Ts'ìnch? man's lung probably were due to an inhalation of particles in open fires. Gold and lead particles are most likely of an environmental origin and may have been inhaled and could have impacted his health and his Champagne and Aishihik First Nations (CAFN) contemporaries.

     

Simulation of the population dynamics and social structure of the Virunga mountain gorillas

An agent-based model was developed to simulate the growth rate, age structure, and social system of the endangered mountain gorillas (Gorilla beringei beringei) in the Virunga Volcanoes region. The model was used to compare two types of data: 1) estimates of the overall population size, age structure, and social structure, as measured by six censuses of the entire region that were conducted in 1971-2000; and 2) information about birth rates, mortality rates, dispersal patterns, and other life history events, as measured from three to five habituated research groups since 1967. On the basis of the research-group data, the "base simulation" predicted a higher growth rate than that observed from the census data (3% vs. 1%). This was as expected, because the research groups have indeed grown faster than the overall population. Additional simulations suggested that the research groups primarily have a lower mortality rate, rather than higher birth rates, compared to the overall population. Predictions from the base simulation generally fell within the range of census values for the average group size, the percentage of multimale groups, and the distribution of females among groups. However, other discrepancies predicted from the research-group data were a higher percentage of adult males than observed, an overestimation of the number of multimale groups with more than two silverbacks, and an overestimated number of groups with only two or three members. Possible causes for such discrepancies include inaccuracies in the census techniques used, and/or limitations with the long-term demographic data set obtained from only a few research groups of a long-lived species. In particular, estimates of mortality and male dispersal obtained from the research groups may not be representative of the entire population. Our final simulation addressed these discrepancies, and provided a better basis for further studies on the complex relationships among individual life history events, group composition, population age structure, and growth rate patterns.     

Inter-group encounters and female transfer in mountain gorillas: Influence of group composition on male behavior

This paper examines the behaviors used by male gorillas (G. gorilla beringei) to influence female choice during inter-group encounters. Encounters are related to the acquisition of females rather than to the defense of a group's range. Data on 58 independent encounters confirms that encounters are generally aggressive, but that contact aggression is less frequent than previously reported. A high number of potential migrants in one of the groups involved, rather than the newness of either group, predicts the likelihood of contact aggression between males. Encounters with a newly formed unit last longer than encounters involving established groups. Male herding serves to prevent female transfer. Females without dependent offspring are more likely than others to be herded. Proceptive females are the target of herding more often than non-proceptive cycling females. Groups where herding has been observed are more likely to be newly formed, and they include significantly more males. This last result confirms that there are advantages to male cooperation in gorillas. It also raises the question of why such cooperation does not occur more often. © 1993 Wiley-Liss, Inc.     

Transport of dead infant mountain gorillas by mothers and unrelated females

This report describes prolonged carriage of the corpses of two mountain gorilla infants by both related and unrelated adult females. Two hypotheses regarding this transport are considered: 1) that maternal behavior toward unrelated infants may be a by‐product of the hormonal condition of pregnancy, and 2) that the animals may be “learning to mother,” as nulliparous females could benefit from the experience of handling an infant that is no longer alive. Some factors pertinent to the event of infant deaths in captivity are considered. Zoo Biol 23:375–378, 2004. © 2004 Wiley‐Liss, Inc.     

Mitochondrial DNA variation and biogeography of eastern gorillas

Mitochondrial DNA variation in 109 individuals from four populations of wild living gorillas in East Africa was ascertained by sequencing the first hypervariable segment of the control region, or 'd-loop', amplified from noninvasively collected hair and faeces. D-loop haplotypes from eastern gorillas fell into two distinct clades, each with low levels of genetic diversity; most observed haplotypes within each clade differing by only one or two mutations. Both clades show evidence of population bottlenecks in the recent past, perhaps concomitant with the tropical forest reduction and fragmentation brought on by global cooling and drying associated with the last glacial maximum.     

Using behavior to determine immature life‐stages in captive western gorillas

Ontogenic development is divided into infant, juvenile, adolescent and adult life‐stages. Although the developmental trajectory of an individual is a flexible entity, which differs within species, environment and sex, life‐stage classifications are generally structured, age‐based systems. This invariably leads to rigidity within a dynamic system and consequently hampers our understanding of primate life history strategies. We propose that life‐stage classifications should be quantitative, flexible entities, which use a reliable measurement of development. Here, we provide a methodological example where placement into a life‐stage is based upon behavioral variance between other similar‐aged individuals. Behavioral data were collected from 12 male (3–11 years old) and 9 female (3–8 years old) captive immature western gorillas (Gorilla gorilla gorilla) housed in five family groups, using continuous focal sampling; 900 hr of data were collected over 131 days. Data were applied to four published life‐stage classifications for mountain gorillas (Gorilla beringei beringei), which showed variable ability to determine life‐stage in western gorillas. A new life‐stage classification (Hutchinson & Fletcher) was proposed specifically for western gorillas, whereby multiple co‐varying behavior provided a robust measure of linear development across immaturity. Each life‐stage was found to be a distinct ontogenic phase and the classification discriminated life‐stage with a high level of accuracy. Using the Hutchinson & Fletcher classification we provide evidence for disparity in developmental trajectories between the sexes from the juvenile period onwards. To expand the understanding of primate life histories, we propose that flexible classifications should be used to enable comparison of allometric life history traits within and between species, from birth onwards. Am. J. Primatol. 72:492–501, 2010. © 2010 Wiley‐Liss, Inc.     

Plant choice in the construction of night nests by gorillas in the Bwindi Impenetrable National Park, Uganda

We investigated the choice of plants in nest sites and individual night nests of a group of gorillas (Gorilla beringei) in Bwindi Impenetrable National Park, Uganda. Most of the nests were built on the ground in secondary forest or canopy gaps. The gorillas used 62 plant genera in their nests out of a possible 108 plant genera available in the immediate environment. This group of Bwindi gorillas chose nest sites nonrandomly with respect to habitat type and selected nest sites in which Pteridium spp. or Mimulopsis spp. were the dominant plants. The Bwindi gorillas selected Pteridium spp. and Ipomea spp. to construct their individual night nests in greater quantities compared to their proportional availability in the immediate environment.     

Patterns of paternity and group fission in wild multimale mountain gorilla groups

To understand variation among social systems, it is essential to know the relative reproductive success of individuals in group-living species. Particularly interesting for such studies are taxa such as mountain gorillas in which both one-male and multimale groups are common, because of the opportunity to estimate the costs and benefits to males of pursuing different reproductive strategies. We genotyped 68 individuals from two groups of multimale mountain gorilla groups in Bwindi Impenetrable National Park, Uganda to determine the distribution of paternity among the males. In both groups, the dominant male sired the majority of offspring. One group underwent a fission, and we found that the eight offspring assigned to the dominant silverback (and their mothers) remained with their father, while the two offspring of unknown paternity ended up in the small group headed by the formerly subordinate silverback. This is consistent with the proposal that the outcome of group fission in primates is not only influenced by maternal relationships among individuals, but also by patrilineal relationships. Results of this study show that subordinate males may gain reproductive benefits even while queuing for dominance status. Despite ecological differences between Bwindi and the Virunga Volcanoes, male mountain gorillas living in both populations benefit from remaining in multimale groups.     

Nuclear integrations of mitochondrial DNA in gorillas

Great ape systematics, particularly at the species level and below, is currently under debate, due in part to the recent influx of molecular data. The phylogenies of previously published mitochondrial control region (or D-loop) DNA sequences in gorillas show deep splits within West African gorillas (Gorilla gorilla gorilla), and very high levels of nucleotide diversity in this subspecies. Here we demonstrate that several previously reported D-loop haplotypes from West African gorillas are in all likelihood nuclear integrations of mitochondrial DNA. Revised estimates of the amount and pattern of mitochondrial DNA diversity in gorillas are provided, revealing two reciprocally monophyletic and highly divergent groups of gorillas, concurrent with their geographic distribution.     

Male-immature relationships in multi-male groups of mountain gorillas (Gorilla beringei beringei)

We examined the pattern and possible functions of social interactions between adult males and immatures in three free-ranging, multi-male groups of mountain gorillas (Gorilla beringei beringei). Previous studies conducted during the 1970s when groups contained one to three adult males concluded that male-immature relationships were likely to be a form of low-cost paternal investment [Stewart, Mountain gorillas: three decades of research at Karisoke. Cambridge, UK: Cambridge University Press, 2001]. We evaluated whether this hypothesis still held in groups containing six to nine adult males, or if male-immature relationships might serve other functions (e.g. mating effort, kin selection, or alliance building). Overall, we found that immatures spent the most time near, and interacted most with, the alpha silverback. These behaviors peaked during the period when infants were still quite vulnerable but increasing their independence from their mothers. Such findings suggest that parenting effort remains the primary function of male-immature relationships; however, there is some evidence for the mating effort hypothesis as well.