About 75 species of monkey occur in Africa, but scientists don’t agree on the exact number. Changing climates over time have contributed to the large number of species. Most species of monkeys depend on trees for safety and foraging resources. During dry climate phases, wooded habitats in Africa often became restricted to riverside gallery forests because trees need to grow near water when conditions are arid. As a consequence, monkey populations restricted to riverine forests became isolated from each other and evolved into different species. This is known as speciation. Africa is home to 16 species of colobus monkeys, 13 species of mangabey monkeys, 1 species of macaque, 1 species of gelada baboon, 5 species of baboons in the Papio genus, 2 species of mandrills, and 33 species of guenon monkeys. The diversity of guenon species gives scientists an interesting opportunity to study how these monkeys speciated.
Black and white colobus monkeys are the most common species of colobus monkey.
There are 13 species of mangabey monkeys. Monkeys get isolated from each other during dry climate phases when they become restricted to smaller forest islands separated by unsuitable desert grassland habitat. That explains why there are so many different but closely related species.
There are about 33 species of guenon monkeys.
1 study looked at the entire genome of mona monkeys. Another study looked at the entire genome of 22 species of guenon monkeys.
1 study looked at the entire genome of 22 species of guenon monkeys. Scientists believe monkeys began to diverge from each other about 10-15 million years ago. The study found genetic evidence of ancient hybridization which contributed to speciation. Species of monkeys isolated for a long enough time to become distinct species hybridize when populations come back into contact with each other following climate change. This hybridization contributes to further speciation. Populations isolated during dry climate phases then reconnect during wet climate phases when forest habitats again expand. Scientists found that some modern species of guenon can hybridize with each other and produce fertile offspring despite having been isolated from each other for 5 million years. Hybrids can eventually evolve into yet another species. Scientists determined clades with the most species are more admixed.
Another study looked at the genome of just 1 species of guenon–the mona monkey (Cercopithecus mona). There are eastern and western populations of this species separated by the Niger River. Scientists who wrote this study determined the 2 populations diverged 84,000 years ago. The eastern population shows evidence of hybridization with their closest relatives, but the western population does not. Scientists think these populations are beginning to evolve into different species. Guenon monkeys have rapidly evolved resistance to the malaria virus–another interesting discovery of this study.
Some speciation can also occur when populations of the same species stay in contact with each other. Some populations of monkeys become better adapted to different tree canopy levels. Monkeys preferring to forage on the ground or lower in the tree canopy may stop mating with monkeys that forage higher in the tree canopy and speciation may occur as a result of this difference in preferences. Monkeys in these situations may evolve different color patterns and physical appearances and stop recognizing monkeys with different preferences as potential mates.
References:
Ayoola, A. et al
“Population Genomics Reveals Incipient Speciation, Introgression, and Adaptation in the African mona monkey (Cercopithecus mona)”
Molecular Biology and Evolution 38 (3) 2021
https://academic.oup.com/mbe/article/38/3/876/5912538
Jensen, A. et al
“Complex Evolutionary History with Extensive Ancestral Gene Flow in an African Primate Radiation”
Molecular Biology and Evolution 40 (12) December 2023
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