Blog 1: Mountain Gorillas


            A male Mountain gorilla (Gorilla beringei beringei). Photograph by Thomas Fuhrmann.

Taxonomy

The following paragraph describes the Mountain gorilla’s taxonomic clades under the Linneaus classification system. 

Similar to all species of primates, such as tarsiers, monkeys, and apes (including humans), the Mountain gorilla (Gorilla beringei beringei) belongs to the Suborder known as Haplorrhini (Lang, 2005). This taxonomic clade shares common physical traits such as a dry nose, a postorbital plate on the skull’s maxilla, and large brains. Gorillas, as well as apes and African and Asian monkeys, belong to the Infraorder known as the Catarrhines. Apes such as chimpanzees, and gibbons, gorillas fall under the Superfamily known as Hominoidea. The great apes, such as orangutans, bonobos, humans, and gorillas, are also found in the Hominidae family. These species share similar characteristics, such as a large body-to-brain size ratio and the formation of complex social groups. Central Africa has two gorilla species: the western gorilla (G. gorilla) and the eastern gorilla (G. beringei) (GAP Project, n.d.). The Mountain gorilla is a subspecies of eastern gorilla and is closely related to the Eastern lowland gorilla (G. b. graueri) (GAP Project, n.d.).



Taxonomic cladogram of modern primate species with numbers depicted in millions of years (mya). The Mountain gorilla can also be placed within the clade of the western gorilla (G. gorilla). Diagram illustrated by Bininda-Emonds et al., 2007. https://doi.org/10.1016/B978-0-12-374928-4.10013-6


Morphology


The Moutain gorilla, along with the other three subspecies, is one of the largest members of the primates. Specifically, this species of eastern gorilla is the second-largest primate in the world (the Eastern lowland gorilla’s mass and height are significant compared to the Mountain gorilla's) (Downey, 2019). Mountain gorillas possess noticeable features compared to other great apes, including a robust, muscular physique and long black to brownish fur covering their head and body (Lang, 2005). The long hairs allow these species of gorillas to become insulated in high-altitude mountainous terrain. Male and female Mountain gorillas are sexually dimorphic, meaning that both sexes have different morphological features. On average, females can weigh up to 97.7 kilograms and stand up to 1.5 meters tall (Rowe, 1996). However, males can weigh around 159.2 kilograms and have a height of 1.8 meters (Rowe, 1996). In addition, male Mountain gorillas have prominent features that distinguish them from females, such as a longer head shape (due to the extension of their skull’s sagittal crest), and sexually mature males develop a silver-white fur coloring on their dorsal and lateral sides of their body. These males are called silverbacks, while juvenile males are called blackbacks (Downey, 2019).




A photograph comparing the size difference between a Mountain gorilla and a park ranger in Uganda.


Life History


The average lifespan for a Mountain gorilla in the wild can be 30 - 40 years. However, a few of these gorilla subspecies can live up to 50 years in captivity (Lang, 2005). Male Mountain gorillas can reach sexual maturity from 12 to 13 years old (Gorillas facts: the largest living primate, n.d.). According to a 2017 study, a male can copulate with a female at around 8.6 years old (Galbany et al., 2017). On the other hand, female gorillas reach sexual maturity at around 7 to 8 years old.

The average gestation period for a mature female Mountain gorilla to nurture her developing offspring is around 8.5 months. After birth and the first three years of the infant’s life, the mother provides care and protection to her offspring (Lang, 2005). When the infant’s growth increases, the time spent with its mother decreases, allowing the offspring to explore and learn skills from their community. The grown juvenile is weaned from its mother when it reaches three to four years old and remains a subadult to approximately six years old (Lang, 2005).

   

Conservation Status


            The population of the world’s remaining 1,063 Mountain gorillas is only found within the African countries of the Democratic Republic of the Congo, Rwanda, and Uganda (Mountain gorilla population news, n.d.). Due to low population densities, a few troops of gorillas live within the high-altitude rainforests of the Virunga Mountains, and the remaining populations are located in Uganda’s Bwindi Impenetrable National Park (Lang, 2005).

            Due to the low numbers of Mountain gorillas in their natural habitat, the International Union for Conservation of Nature’s (IUCN) Red List classified this species as ‘endangered’ in 2018 (Greer et al., 2018). The primary factors of the fate of these large primates are the ongoing threats of habitat destruction, mining explorations, the spread of airborne pathogens and skin diseases, climate change, poaching, and civil conflicts in the Democratic Republic of the Congo (Threats, n.d.).


References:

Downey, K. (2019). Mountain Gorilla, Gorilla beringei beringei. New England Primate Conservancy. https://neprimateconservancy.org/mountain-gorilla/#:~:text=As%20the%20second%2Dlargest%20primate,between%2040%20and%2050%20years.

Galbany, J., Abavandimwe, D., Vakiener, M., Eckardt, W., Mudakikwa, A., Ndagijimana, F., Stoinski, T. S., & McFarlin, S. C. (2017). Body growth and life history in wild mountain gorillas (Gorilla beringei beringei) from Volcanoes National Park, Rwanda. American Journal of Physical Anthropology, 163(3), 570–590. https://doi.org/10.1002/ajpa.23232

GAP Project. (n.d.). Gorilla: the “gentle giants.” Gorilla - GAP Project. https://www.projetogap.org/en/species/gorilla/

Gorillas facts: the largest living primate. The Gorilla Organization. (n.d.). https://gorillas.org/about-gorillas/gorilla-facts/#:~:text=Female%20gorillas%20become%20sexually%20mature,of%2015%20(on%20average).

Greer, D., Hickey, J.R., Robbins, M.M., Stoinski, T.S., Gilardi, K.V., Basabose, A., & Nampindo, S. (2018, July 31). Mountain gorilla. IUCN Red List of Threatened Species. https://www.iucnredlist.org/species/39999/176396749

Lang, K. (2005, October 4). Primate factsheets: Gorilla (Gorilla) taxonomy, morphology & ecology. Wisconsin National Primate Research Center. https://primate.wisc.edu/primate-info-net/pin-factsheets/pin-factsheet-gorilla/ 

Mountain gorilla population news. (n.d.). Virunga National Park. https://virunga.org/news/recent-survey-shows-continued-growth-among-the-worlds-last-remaining/ 

Rowe, N. (1996). The pictorial guide to the living primates. Pogonias Press.

Saltzman, W., Tardif, S. D., & Rutherford, J. N. (2011). Hormones and reproductive cycles in primates. In Hormones and reproduction of vertebrates (pp. 291-327). [Diagram]. Academic Press. https://doi.org/10.1016/B978-0-12-374928-4.10013-6

Threats (n.d.). International Gorilla Conservation Programme (IGCP). https://igcp.org/mountain-gorillas/threats/

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