Mandrillus

Mandrillus is a genus of large Old World monkeys distributed throughout central and southern Africa, consisting of two species: M. sphinx and M. leucophaeus, the mandrill and drill, respectively.<ref name="www.itis.gov">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Mandrillus, originally placed under the genus Papio as a type of baboon, is closely related to the genus Cercocebus.<ref name="Dixson, Alan F.">Template:Cite book</ref> They are characterised by their large builds, elongated snouts with furrows on each side, and stub tails. Both species occupy the west central region of Africa and live primarily on the ground.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> They are frugivores, consuming both meat and plants, with a preference for plants.<ref name="Dixson, Alan F." /> M. sphinx is classified as vulnerable and M. leucophaeus as endangered on the IUCN Red List of Threatened Species.<ref name="IUCNMandrill"/><ref name="IUCNDrill"/>

Taxonomy

Mandrillus is a genus within the tribe Papionini, which in turn is under the subfamily Cercopithecinae. This subfamily is classified under the family of Old World monkeys (Cercopithecidae) within the infraorder Simiiformes.<ref name="www.itis.gov" /> The Papionini tribe contains six other genera: baboons (Papio), macaques (Macaca), crested mangabeys (Lophocebus), white-eyelid mangabeys (Cercocebus), the highland mangabey (Rungwecebus) and Theropithecus.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref>

Originally, both species were considered part of the Papio genus, as forest baboons, due to superficial similarities such as size and appearance, particularly in facial features.<ref>Template:Cite journal</ref> However, studies conducted analysing anatomical and genetic differences between the current Mandrillus and Papio genera showed more differences than similarities resulting in the current taxonomic ranking.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Furthermore, the studies showed Mandrillus are more closely related to the white eyed mangabeys, and diverged relatively recently (4 million years ago) from this genus.<ref name="Dixson, Alan F." />

Anatomy

File:Mandrillus leucophaeus 01 MWNH 297.jpg

Mandrillus leucophaeus skull

Both species of Mandrillus develop extremely large muzzles, prominent nasal ridges and paranasal swelling (swelling in the area adjacent to the nostrils). The size and colour of the paranasal swellings correlate to male dominance and rank, while the size of nasal ridges is a way of attracting mates.<ref name="Lehman">Lehman, S., & Fleagle, J. (2006). Primate Biogeography Progress and Prospects . Boston, MA: Springer US.</ref> Mandrillus teeth consist of two incisors, two premolars, one canine and three molars in each half of the upper and lower jaw, totalling 32 teeth.<ref name="Dixson, Alan F." /> Furthermore Mandrillus display larger premolars and extended canines; these dental traits are better adapted to crushing hard objects. This is due to a large part of their diet consisting of hard, dry nuts and seeds that require greater crushing power and the use of their teeth in ripping apart rotting wood to search for insects and other invertebrates.<ref name="Fleagle-2002">Template:Cite journal</ref>

File:Mandrillus sphinx MNHN.jpg

Mandrillus sphinx skull and shoulder blade

Within the shoulder and upper arm structures of the Mandrillus monkeys a deep scapular, broad deltoid plane, narrow stable elbow region and other skeletal features indicate the use of the forelimbs for climbing and foraging.<ref>Template:Cite journal</ref> This is used by the monkeys to climb trees when searching for ripe fruit and in the aggressive foraging of the forest floor in search of food.<ref name="Fleagle-2002" /> Mandrillus monkeys have developed an extremely broad and robust ilium, and a rounded tibial shaft. The development of these features can be attributed to the climbing of trees and quadrupedal locomotion. The largest toe is separated from the remaining toes for increased grasping power when climbing trees.<ref name="Dixson, Alan F." />

Sexual dimorphism

Both species of Mandrillus demonstrate a great degree of sexual dimorphism in weight, anatomy and physical appearance. The mandrill displays the most extreme sexual dimorphism for weight among all primates, with a male-female weight ratio of 3.2 – 3.4 at eight to ten years of age.<ref>Template:Cite journal</ref> Similarly, drills are one of the most sexually dimorphic primates for body weight, with a male growing up to 32 kg while a female grows to 12 kg. Sexual dimorphism is also displayed in the growth of the craniofacial bones of both species.<ref name="Elton-2006">Template:Cite journal</ref> The males of each species have longer muzzles, much larger paranasal swellings and longer canines than their female counterparts. In a study of wild drills, female muzzles only grew up to 70% the length of the male muzzles.<ref name="Dixson, Alan F." /><ref name="Elton-2006" /> Furthermore, males have brightly coloured, saturated rumps unlike their female counterparts.<ref name="Dixson, Alan F." /> Both species also display the greatest visual sexual dimorphism within monkeys. On a scale based on rating the differences in physical features between genders, the mandrill obtained 32 whilst the drill obtained 24.5.<ref name="Dixson, Alan F." /> These ratings are based on features such as the saturation and colour of the rump (and face for mandrills), the paranasal swelling, the fatted rump and fur colouring.<ref name="Dixson, Alan F." />

Distribution and habitat

Mandrillus monkeys have a very localised biographical region located in West central Africa. The two species are often considered allopatric,<ref name="Lehman" /><ref name="Dixson, Alan F." /> they occupy non-overlapping regions, and their regions are divided by a physical barrier, the Sanaga river in Cameroon. Mandrillus leucophaeus occupy the area above the river in North western Cameroon and southwestern Nigeria up until the Cross River, and Bioko Island (Equatorial Guinea) which lies off the coast.<ref name="Lehman" /><ref name="Dixson, Alan F." /> The mandrill occupies the area below the river line in Cameroon, Río Muni, Gabon and Congo.<ref name="Lehman" /> The Mandrillus species occupy multiple sections of the Guinean forests of West Africa, including Cross–Sanaga–Bioko coastal forests and Cameroonian Highlands forests.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Lehman" /> The forests the monkeys occupy have a humid, tropical climate and rugged terrain. Deforestation has reduced the habitat of both Mandrillus species, reducing the distribution of each species, especially the drill.<ref name="Dixson, Alan F." />

Behaviour

Diet

Both Mandrillus species are frugivores, consuming both plants and insects with a preference for fruits and nuts. Mandrillus species spend a large amount of their time foraging through the forest in search of food.<ref name="Nsi Akoue-2017">Template:Cite journal</ref> In a study conducted in Cameroon, approximately 84% of the faecal matter of mandrills consisted of fruit.<ref name="Dixson, Alan F." /> Similarly, a study done on drills in southwest Cameroon showed that the mean weight of fruit and seed in faecal matter was equal to or greater than 80%.<ref>Template:Cite journal</ref> Seasonal changes can be seen within Mandrillus diet, during peak fruit season (September to March) their diet consisted mostly of fruit, pulp and seeds whilst during the fruit scarce season (June to August) there was a great increase in the consumption of insects, woody tissue and especially nuts.<ref name="Hongo-2018">Template:Cite journal</ref><ref name="Dixson, Alan F." /> There was also an increase in the variation of the diet during the fruit-scarce season.<ref name="Hongo-2018" /><ref name="Astaras-2008">Template:Cite journal</ref> Important fruit include but are not limited to, the fruit of the bush mango (Irvingia gabonensis), African Corkwood tree (Musanga cecropioides), Grewia coriacea, Sacoglottis gabonensis and Xylopia aethiopica. Invertebrates consumed include crickets, ants, caterpillars and termites. Rarely, Mandrillus monkeys will eat larger animals, such as rats and gazelles when presented with the opportunity.<ref name="Nsi Akoue-2017" /><ref name="Dixson, Alan F." /><ref name="Astaras-2008" />

Social systems

The species of the genus exhibit great similarities in their social systems. Both generally form smaller groups, however the size of these groups is unclear. A study done on drills in southwest Cameroon found a mean group size of 52.3<ref name="Astaras-2008" /> while another more recent report stated a figure of 25–40 on these smaller groups.<ref name="Marty-2009">Template:Cite journal</ref> A study of mandrills done at Campo reserve in Cameroon found small groups contain 14 - 95 individuals.<ref name="Dixson, Alan F." /> These smaller groups, with stable social structures, often join to form larger "supergroups" of hundreds of individuals.<ref name="Marty-2009" /> Some of the largest mandrill "supergroups" reported contained up to 845 individuals whilst some of the largest drill "supergroups" reported contained 400 individuals.<ref name="Nsi Akoue-2017" /><ref name="Dixson, Alan F." /> There have been reports of solitary male Mandrillus monkeys, however this occurs very rarely.<ref name="Dixson, Alan F." />

The social structures and social hierarchy of Mandrillus "supergroups" and groups is highly contentious. There are multiple older (1970s-1990s) sources referencing single male units, which contained a male and multiple female monkeys, as the smallest and most common stable social structure. However this has been disproved with the discovery of less colourful male Mandrillus and further observations of behaviour.<ref name="Dixson, Alan F." /><ref name="Bret-2013">Template:Cite journal</ref><ref name="Astaras-2008" /><ref>Template:Cite journal</ref> Mandrillus leucophaeus social structures are unknown, due to low populations, and secluded habitats with dense forestry.<ref name="Marty-2009" /> On the other hand, Mandrillus sphinx has had a variety of studies on social structure done in largely captive and semi-free ranging settings, with few studies on wild mandrills. The current studies on mandrills are inconclusive, and present different results. Various semi-free ranging studies conducted report a matrilineal social structure with a stable infant and female mandrill "supergroup". Male Mandrillus monkeys would disperse from this group when old enough and join other groups only during mating season.<ref name="Bret-2013" /><ref name="Dixson, Alan F." /> Further studies, also done in semi-free ranging settings, conclude that dominant females are central to group cohesion and connectivity (how close they remained).<ref name="Dixson, Alan F." /><ref name="Bret-2013" /> Conversely, a study on wild mandrills published in 2015 reported that a stable adult, male mandrill population of 5 - 6 was present year round in "supergroups".<ref name="Brockmeyer-2015">Template:Cite journal</ref> This aligned with the social structures reported in other research papers done on wild mandrills, where stable multi-male and multi-female groups were found.<ref>Template:Cite journal</ref><ref name="Brockmeyer-2015" /><ref name="Astaras-2008" /> This difference in social structures between Mandrillus groups has been attributed to limitations in observing wild mandrills, differing habitats, and differing sample sizes.<ref name="Bret-2013" />

Male dominance and rank have been linked to the colouration and colour extension of the rumps, greater saturation and colour extension correlated to higher-ranking males. Males of higher ranking are more likely to associate with females, especially those with sexual skin swelling, and more likely to successfully mount females.<ref name="Marty-2009" /><ref name="Dixson, Alan F." /> Dominant, adult males practice mate guarding on adult females during times of maximal skin swelling; with their high competitive ability they are more likely to successfully reproduce.<ref name="Marty-2009" /> Due to the tropical habitat, mating season coincides with the dry season (May to October) and birth season coincides with the wet season (November to April).<ref name="Dixson, Alan F." />

Communication

File:Mandrillus sphinx (alpha male).jpg

Mandrill displaying silent baring of teeth

The Mandrillus genus uses both visual and vocal forms of communication, which are extremely similar or identical across both species. Both species have three identical long-range vocal communications: two-phase grunts, roars and "crowling".<ref name="Dixson, Alan F." /> The two-phased grunt is a low, two-syllable continuous sound used exclusively by adult males during calm group progression and mate guarding.<ref name="Kudo-1987">Template:Cite journal</ref> Roars are single low, single syllable sounds used exclusively by males in the same context as two-phase grunts. Crowling is used by infants and females during group movement or foraging to call together the dispersed group.<ref name="Kudo-1987" /><ref name="Dixson, Alan F." /><ref>Template:Cite book</ref>

They also use numerous short-range vocal sounds for various purposes. The "yak" and grinding of teeth are used during tense situations. The grunt is used in aggressive situations and screams are used to escape or while experiencing fear. The growl is used to convey mild alarm, the K-alarm is used to convey intense alarm and the "girney" is used for appeasement.<ref name="Kudo-1987" /> Both species use various facial expressions to communicate with each other. The silent baring of teeth is a positive visual signal conveying peaceful intentions, and it is often combined with a shaking head.<ref>Template:Cite journal</ref> Staring open-mouthed is a display of aggression, frowning with bare teeth is used to encourage submission, staring with bare teeth can communicate aggression or fear, pouting signals submission and a relaxed open mouth encourages playing.<ref name="Dixson, Alan F." />

Conservation status

The current conservation status of Mandrillus sphinx is vulnerable and that for Mandrillus leucophaeus is endangered.<ref name="IUCNDrill"/><ref name="IUCNMandrill"/> The greatest threats to the conservation of this genus are the severe loss and degradation of their habitat, and hunting.<ref name="Morgan-2013">Template:Cite journal</ref><ref>Template:Cite book</ref> The loss of habitat is an ongoing threat that can be attributed to the expansion of human settlements as well as the clearing of forests for chipping factories and agriculture. Hunting and poaching of Mandrillus monkeys for meat or to protect crops is also major, ongoing threat to the population despite the implementation of hunting restrictions and sanctuaries.<ref name="IUCNMandrill"/><ref name="IUCNDrill"/> The drill population in Cameroon, which encompasses 80% of the drill's original habitat, has been fragmented into smaller, isolated populations with largest residing in Korup national park.<ref name="Morgan-2013" /> The mandrill population in south Cameroon and Equatorial Guinea are at great risk due to extensive forest loss. The majority of the mandrill population remains in Gabon and faces major threats from railroad construction and logging companies.<ref name="Dixson, Alan F." /> As of 2020, the mandrill population is in decline while the drill population is not able to be accurately determined.<ref name="IUCNMandrill"/><ref name="IUCNDrill"/>

Sources

• Template:Cite book

External links

• Primate Info Net Mandrillus Factsheets