Genetic diversity and divergence in the endangered Cape Verde warbler Acrocephalus brevipennis

Genetic factors play an important role in the long-term persistence of populations and species, and conservation strategies should take such factors into account. We use neutral molecular markers to assess diversity and divergence between the three remaining island populations of a little-studied endemic passerine, the Cape Verde warbler Acrocephalus brevipennis. Variation at both microsatellite loci and the cytochrome b gene reveal low diversity within the species overall, but considerable divergence among the populations on Santiago, Fogo and São Nicolau islands. The genetic markers show a gradient of genetic diversity with population size, with the smallest population of S. Nicolau being the least diverse, and the largest, Santiago, the most diverse. The more geographically isolated population on S. Nicolau is also more divergent from Santiago and Fogo than these two are from each other. The Cape Verde warbler diverged from its sister species, the greater swamp warbler Acrocephalus rufescens, within the last million years, and the three populations became isolated from one another 165,000–199,000 years ago. There is also evidence of population bottlenecks, especially on S. Nicolau. This population seems to have decreased during the last century, with potential for further decreases and even extinction. As the three populations are genetically distinct, with no evidence of gene flow between them, we argue they should be treated as separate management units for the successful conservation of this species.