Primatology.net

Most people possessing any familiarity with our closest relatives know that there are two species of chimpanzees: Bonobos (Pan paniscus) and the common Chimpanzee (Pan troglodytes). Some researchers believe that bonobos and common chimps diverged around 0.9 million years ago (Won and Hey, 2002).

Many may not know that taxonomies further divide common chimps into three subspecies, represented by three distinct populations separated by geographic divisions (e.g. distance, rivers). They are the Western, Central, and Eastern, known as Pan troglodytes versus, Pan troglodytes troglodytes, and Pan troglodytes schweinfurthii, respectively (Groves, 2001).

Previous genetic studies, combined with the nearly complete absence of behavioral or morphological differences, have led some to conclude that the populations are not distinct subspecies (Fischer et al., 2004). In contrast, a new study by researchers from four different institutions seems to show that the three common chimpanzee populations are indeed genetically distinct, and that little or no gene flow occurs between the groups (Becquet et al., 2007).

Recently published in PLoS Genetics, Genetic structure of chimpanzee populations reports on the largest genetic study of chimps to date. They analyzed the genetic material from 84 individuals: 6 bonobos and 78 common chimpanzees.

Their conclusions:

• The western, central, and eastern subspecies designations correspond to clusters of individuals with similar allele frequencies;
• There is little evidence for admixture between groups in the wild; and
• Central and eastern chimpanzees are most closely related in time to each other than either of them are to western chimps.

They failed to find any support for a fourth subspecies (Pan troglodytes vellorosus), originally proposed following mtDNA studies of chimpanzees living near the Sanaga river in Cameroon (Gonder et al., 2006).

References:

• Becquet C, Patterson N, Stone A, Przeworski M, Reich D (2007) Genetic structure of chimpanzee populations. doi:10.1371/journal.pgen.0030066.eor
• Fischer A, Wiebe V, Paabo S, Przeworski M (2004) Evidence for a complex demographic history of chimpanzees. Mol Biol Evol. 21:799-808.
• Gonder MK, Disotell TR, Oates JF (2006) New genetic evidence on the evolution of chimpanzee populations and implications for taxonomy. International Journal of Primatology 27:1103-1127.
• Won YJ, Hey J (2002) Divergence population genetics of chimpanzees. Mol Biol Evol. 22, 297-307.

[Map from Wikipedia]

National Geographic has a short story and video of a newly-discovered population of bonobos in the Democratic Republic of Congo.

The large group may contain as many as 3,000 members, a welcome find for this dwindling population.

Animals that live in groups often break into smaller groups (fission), and later recongregate (fusion). Fission-fusion behavior is often tied to resource availability, but can also be related to social dynamics (competition among group members can lead to conflict, and breaking into smaller groups can alleviate the conflict). While fissioning into subgroups can relieve tension and conflict, bringing the subgroups back together can often be a trigger for aggression.

Spider monkeys live in groups, and break into smaller groups to hunt and eat. It has been noted for some time that when hunting parties return to the larger group, those returning often embrace the waiting spider monkeys.

Scientists from the UK studying two populatations of spider monkeys in the Yucatan have observed that the individuals who engage in this hugging are much less likely to behave in an aggressive fashion, either to each other or to others in the larger group.

Filippo Aureli and Collene Schaffner believe theirs is the first evidence for deliberate conflict management at fusion, and believe it may indicate the reason for similar greetings exhibited by other fission-fusion species such as spotted hyenas, bonobos, and humans.

References:

• Morell V (2007) Hug it out, Monkey. ScienceNOW 21Feb
• Aureli F and Schaffner CM (2007) Aggression and conflict management at fusion in spider monkeys. Biology Letters, Vol 3, no. 2. (published early online)