Pan paniscus × Pan troglodytesEUGENE M. MCCARTHY, PHD GENETICS
EUGENE M. MCCARTHY, PHD Google+ Profile
Hybridization between chimpanzees (Pan troglodytes) and bonobos, also known as pygmy chimpanzees, (Pan paniscus) has occurred in captivity (Vervaecke and van Elsacker 1992, Vervaecke 2002; Vervaecke et al. 2004).
In 1979, a circus director in France bought what he believed to be a male chimpanzee. It performed in acts and regularly mated with two female chimpanzees. This male ape, however, turned out to be a bonobo. Between 1991 and 2000, seven hybrids were produced from these matings, most or all of which survived. By 2000, the oldest was working in the circus act in place of his retired father.
Apparently, natural hybridization between these two apes has not as yet been reported. The ranges of the bonobo and the chimpanzee are separated by the Congo and the Lualaba rivers, so their ranges are essentially allopatric. But contact may occur upstream of Boyoma Falls (formerly known as Stanley Falls) where the river can easily be crossed, at least by humans, during times of low water. Fenart and Deblock (1973, p. 11) note that there is one point there where it is possible to cross by leaping from rock to rock at low water, but that a survey of that area revealed no evidence of natural hybridization. Untrained apes cannot swim and are afraid of water. Moreover, the two rivers in question are crocodile infested. So it seems likely that little opportunity for hybridization exists even in this one region of potential contact.
In a brief abstract of a presentation given at the Spring 2003 meeting of the Primate Society of Great Britain, Vervaecke et al. (2004) state the following: “From historical accounts it appears that natural populations of bonobos and chimpanzees have been allopatric since their
phylogenetic separation. There are no accounts of hybridisation under natural conditions [since they do not normally come into contact with each other under natural conditions]. There is, however, evidence for interbreeding between bonobos and chimpanzees in captivity. We briefly (6.5 h) observed and filmed a small group of four bonobo-chimpanzee hybrids (2 males, aged 10 and 9, and 2 females aged 10 and 8). There was clear individual variation in degree of expression of typical chimpanzee or bonobo features. In each individual, there were anatomical features reminiscent of both of the parental species: the specific bonobo-like pink coloration of the lips, the hairstyle and slender body build, the chimpanzee-like dorsal position of the female genitals, more sturdy body build and prognathism. The behaviours could be categorized less exclusively. We observed mostly female oriented interactions, including grooming, play, approaches and intersexual ventro-dorsal sex. There was one female coalition against the males. The individuals lip-smacked while grooming and performed swaggering displays. The hoots were like chimpanzee pant-hoots with an introduction, build-up and climax in a higher pitched bonobo tone and more ‘e’ than ‘o’ sounds. Studies on Pan in the seventies and eighties emphasised discontinuity between the two species, contrasting the male-dominated, aggressive nature of the chimpanzee to the female-oriented, peaceful nature of the bonobo. In the nineties and in present studies, the continuity among Pan is increasingly being documented. The existence of hybrids challenges our tendency for binary thinking and points at the conceptual relativity of the species gap.
Bonobo × Chimpanzee - © Macroevolution.net