Hybridisation and extinction in a recent Passer sparrow hybrid zone

Hybridisation and introgression play an important role in evolution. Within Passer sparrows for example, hybridisation has led to the evolution of new phenotypes and speciation. However introgression can also be maladaptive and may lead to extinction in some cases. The Cape Verde Islands represents a recent contact zone between three different Passer species - the endemic Iago sparrow (P. iagonensis), the Spanish sparrow (P. hispaniolensis), likely a natural colonisation in 19th Centruy and the House Sparrow (P. domesticus), which was most probably introduced in the early 20th Century. Spanish Sparrows have colonised nearly all the inhabited Cape Verde islands but have gone extinct on at least two of them, seemingly due to the arrival of the House sparrow on the same islands. Remarkably due to ornithological interest in the islands, the arrivals and locations of all Passer species have been well documented since Darwin visited in 1832, during his voyage on HMS Beagle. The Cape Verdes are therefore an excellent location to test biogeographical hypothesis for the colonisation and to examine whether introgression has had maladaptive consequences in these species.