Rapid morphological changes as agents of adaptation in introduced populations of the common myna ( Acridotheres tristis )

Invasive species present an opportunity to test the association between selective forces and adaptive morphological traits because these species can experience rapid changes when introduced to new environments. One such invader is the common myna ( Acridotheres tristis ), a broadly ranging avian species that has been introduced on most continents and many oceanic islands. Here, we studied morphological variability in native and introduced populations of common mynas to identify the key environmental variables correlated with local phenotypic variation during biological invasions. In particular, we aimed to determine whether similar selective pressures acted on populations in the native range and the introduced ranges, and whether the same factors shaped morphological variation in different introduced populations. We recorded eight morphological measurements from 1,331 individuals across sites throughout most of the common myna’s range, as well as climatic, topographic and anthropogenic environmental data, sex and age of individuals, and years since local introduction. We found inconsistent signals of morphological adaptation in the native population, representing different patterns between females and males. Conversely, urbanization was a significant explanatory factor of phenotypic shifts in introduced populations, especially with regards to foraging-related traits. Moreover, we found that adaptation occurred differently across two focal introduced populations (Sydney, Australia and Israel). Therefore, caution is required in studies relating to evolutionary adaptations and predictions made regarding characteristics of invasive populations within a limited range of their introduced ranges. Our results also indicate a major role for urbanization in impacting the shape and size of foraging-related features in this broadly-distributed invasive species, emphasizing the impact of human-induced environmental changes upon the trajectories of biological invasions and, ultimately, their effects on native biodiversity.