Genetic and Morphometric Differentiation in Introduced Populations of Common Chaffinches (Fringilla coelebs) in New Zealand

Abstract

Approximately 400 Common Chaffinches (Fringilla coelebs) were introduced last century into New Zealand from England. These founders and their descendents have been such successful colonizers that they are now among the most abundant and widespread passerine species in the region. To assess the amount of differentiation that has developed in the period of about 90-120 years, we sampled populations in the North and South islands of New Zealand, and a population isolated on Chatham Island 800 km to the east. Chaffinches have differentiated very little genetically and morphometrically, in sharp contrast to colonizing species such as House Sparrows (Passer domesticus), Common Mynas (Acridotheres tristis), and European Starlings (Sturnus vulgaris) introduced contemporaneously. Population differentiation does not fit geographically ordered patterns such as clines or isolation-by-distance, and there is no convincing evidence of selection for climatic adaptation or non-selective environmental induction. Random drift is implicated as the primary causal agent for the haphazard pattern of geographic variation, which implies that genetic and morphometric characters are now effectively neutral with respect to selection. Comparison with populations in Europe, North Africa, and the Atlantic islands suggests that microevolutionary processes of population divergence in New Zealand can be extrapolated through time to explain intraspecific and interspecific diversity in chaffinches.