Genetic Variation in the Chimpanzees of Bossou and Nimba

Mitochondrial DNA (mtDNA) is present in much higher copies, 100–1,000 times more, in a cell than nuclear DNA, and sequencing of mtDNA is not subject to the artifacts such as stutter band or allelic dropout that are common in microsatellite genotyping, which is a popular method used in wildlife conservation studies. Although the scope of mtDNA analysis is limited to matrilineal genetic information, it provides haplotypic information (i.e., DNA sequences without interruptions from recombination). This feature of mtDNA allow us to address interesting questions about Bossou and Nimba chimpanzees, including their breeding history, their genetic relationship, social behavior among matrilineal kin, and genetic diversity. Our mtDNA sequencing of Bossou and Nimba chimpanzees found the following: (1) no clear population structure emerged as in other populations of West African chimpanzee (Pan troglodytes verus), suggesting that gene flow was sufficient in the common ancestral population of West African chimpanzees; (2) there is no matrilineal gene exchange between Bossou and Nimba chimpanzees among the current generations; (3) four of the eight original adult members of the Bossou community are likely matrilineal relatives; (4) so far, the matrilineal genetic diversity of the Bossou community is still relatively stable, but there is a high risk of haplotype extinction because of a skewed haplotype distribution and a predicted relaxation of incest avoidance; and (5) finally, hair samples showed an inferior result to other sample types, such as urine, feces, and wadges (chewed-up fruit remains).