Allopatric speciation and multi-trait variation in the common chaffinch (Fringilla coelebs) complex

Abstract

The common chaffinch (Fringilla coelebs) is a widespread passerine species in the West Palearctic, and is a common breeder in most of Europe, western Asia, northern Africa, and the Macaronesian islands in the Atlantic Ocean. A total of 19 subspecies are described, whereas five of these are located on the Macaronesian Islands. Three subspecies are found in the Canary Islands, one in Madeira, and one in the Azores. Each of these three archipelagos has a unique climate and ecology, and together with the different geological age and the variation in distance to land these archipelagos provide us with a good background to study evolutionary changes and speciation. Differences between populations were studied through several traits: plumage differences, biometry, genetic relationships, and differentiation in sperm morphology. All of these traits showed great variation between archipelagos, islands, subspecies, and populations. The degree of isolation is higher on islands, which might give rise to a larger degree of variation between populations due to drift and selection. The islands subspecies are also generally more differentiated in the studied traits than the populations on the mainland. The sperm measurements show that both the extremes in total sperm length, i.e. the shortest and the longest, are found on the Macaronesian Islands. Also, the variation between archipelagos is greater than the variation between the continental populations, even if the geographical rage on the mainland is of a much greater character. Not surprisingly, the variation among the continental populations is more gradual. Total sperm length, for example, gradually decreases from Morocco to Norway. The colonization history of the Macaronesian islands is not well understood, but my data support the hypothesis of Marshal and Baker (1999). They argue for a North African origin of the common chaffinch, and that the radiation followed two main routes: one colonizing the Macaronesian islands, while the other spread northwards trough Europe. A Macaronesian colonization from the mainland, to the Azores, trough Madeira, and finally to the Canary Islands seems most likely. Further, the homogeneity on all measured traits among the Azorean populations is in contrast to the large differences between populations in the Canary Islands. Different levels of gene flow among the Azores and the Canary islands can be the origin of these findings.