Population structure of brood parasitic Vidua species

The ten species of African indigobirds in the genus Vidua are of particular interest in comparison with other brood parasites because of their high degree of host-speificity. Most species of indigobirds parasitize a single species of estrildid finch. As nestlings, indigobirds imprint on the song of their host species, and in their adult life, male indigobirds mimick the learnt host song, while females choose mates singing the song they heard from their foster parents. Assortative mating among birds reared by the same host species leads to reproductive isolation between indigobird groups associated with different hosts. Indigobirds are widespread in open woodlands, agricultural and semi-arid land from Senegal to South Africa, with overlapping ranges of individual species. Although quite similar, indigobirds can be distinguished morphologically by plumage, beak and feet coloration. Young indigobirds mimick the different mouth markings that are displayed by the nestlings of their foster species; doing so, they secure the care of their foster parents while they are raised together with their hosts true offspring. Mouth mimicry is clearly a genetic adaptation to the use of different host species. Comparisons of host and parasite phylogenies suggest that independent colonization events rather than parallel evolution caused the extant host-parasite associations. Genetic analysis of mitochondrial DNA sequences and nuclear microsatellite polymorphisms (first year of funding) indicated significant differentiation among the indigobird species in both genomes. The degree of differentiation, however, was lower than might be expected considering the morphological differences and the assortative mating behavior. For a second year of research on population genetics and speciation of indigobirds, I propose to ask the question whether the incomplete genetic differentiation among the indigobird species is due to retained ancestral polymorphism or to a high level of gene flow between the species. The analysis of the genetic continuity within species over geographic space and the differentiation between local populations of sympatric species shall shed light on the origin of indigobird species: Do indigobird populations originate from an isolated colonization of a new host and subsequent spread from that point of origin, or did they arise from multiple colonization events occurring at different times in different areas? Quantitative differences of measures of nuclear and mitochondrial gene flow will be evaluated with the help of population genetics models and simulations to draw inferences on population dynamics and equilibrium conditions. In order to identify demographic changes like bottlenecks and population growth from the genetic data, I plan to increase sample sizes of local populations. Finally, I propose to explore whether the inclusion of additional mt sequence data to the mtDNA trees would increase or decrease the estimate of genetic structure and the inferred minimum number of host switches.