This project is using a "natural experiment" to investigate an evolutionary phenomenon that has rarely been considered, let alone studied in the field, yet which may have been of great importance in the history of life. Species, considered the basic units of natural diversity, are supposed to follow a one-way evolutionary trajectory, becoming isolated first physically, then reproductively. After that crucial point, a species is genetically independent; it can acquire new variation, and the potential to evolve, only via mutation. A new species that survives does so by carving itself a slice of ecological space, and in doing so often becomes narrower, more specialized, in its behavior and adaptations. This canonical pattern is undoubtedly frequent and central to the process of evolutionary diversification. Some evidence suggests, however, that the speciation process is not always irreversible; that under circumstances that are unusual, but not impossibly rare, populations belonging indisputably to different species can dissolve the reproductive barrier and form a new species by fusion. Once completed, such fusions are much harder to recognize than instances of conventional, splitting speciation. Indeed, the best evidence for them often comes from molecular genetic information of a kind unavailable until very recently. This project uses both observational and genetic data to test the hypothesis that populations belonging to two species of monkeys in the Gombe National Park, Tanzania, are in the midst of such a process. Red-tailed monkeys (Cercopithecus ascanius) and blue monkeys (C.mitis) are good species, quite distinct in appearance and behavior. Over most of the broad area where both occur, they rarely hybridize, and hybrids are apparently unsuccessful. In Gombe National Park, however, interbreeding over many generations has established hybrids as a substantial minority within the breeding population. The study is testing the hypothesis that unusual biogeographic and demographic conditions at Gombe have driven the two species towards genetic and behavioral integration. The Co-PI's field survey will quantify the density of parental species and hybrids, and relate these to the distribution of forest habitat. Behavioral data will be used to test the speculation that at Gombe both C.mitis and C.ascanius tend to relate to hybrids, and members of the other species, with behaviors normally reserved for conspecifics. The genetic phase of the study will take advantage of recent technical advances that allow genetic material to be recovered from "biodetritus" - such as feces. Genetic markers specific to the two monkey species will be used to track the ancestry of individual monkeys in the Gombe population, and hence infer the patterns of gene flow between the populations and into the hybrids. The resulting PhD will qualify a female scientist, with a proven teaching and public service record, to enter the academic community. The fieldwork itself involves international collaboration, and practical scientific training of personnel in the host country, Tanzania. More broadly, it should also help to inform the general public about the nature of biological evolution.
