Evolution in the introduced New Zealand populations of the common myna, Acridotheres tristis (Aves: Sturnidae)

Abstract

Common mynas were introduced into New Zealand from Australia in the 1870's. Seventy birds released at Wellington have apparently given rise to populations that now occur almost exclusively north of latitude 40° S. Morphometric variation in 28 characters of 307 adults was assessed statistically, based on eight samples spanning their New Zealand range. Univariate analysis revealed that 17 characters of males and 13 of females varied significantly among localities and that birds tend to be larger in the north. Discriminant analysis confirmed the north–south pattern of differentiation but disclosed that the newly established northern populations are very similar morphometrically. Both sexes have differentiated among localities in size and shape. Size variation is aligned with temperature only in males, and shape differences are associated with variation in precipitation in both sexes and altitude in females, females have differentiated in fewer characters than males, but overall, they show a stronger relationship between interlocality and intralocality character variability. Although the adaptive basis of increased size in warmer climates is unclear, the consistency of character covariation in localities with different climatic conditions argues against an ecophenotypic explanation. It is therefore concluded that the New Zealand populations are in the early stages of adaptive differentiation.