Two speed invasion: assisted and intrinsic dispersal of common mynas over 150 years of colonization

Aim: Despite the common myna's widespread distribution, and the significant impact it has caused in parts of its non-native range, there have been no comprehensive genomic studies of its invasion of any region. We aimed to characterize the common myna invasion of the Australian continent to understand its population genetic landscape, introduction history, dispersal characteristics, and the interconnectedness between different source populations and invasive fronts. Location: Common mynas from 26 geographical locations spanning the Australian continent were utilized in this study. Taxon: Common myna (Acridotheres tristis). Methods: We used a reduced genome representation method (DArTseq) to generate thousands of single nucleotide polymorphism markers in 462 common mynas. We then applied population genomic techniques to identify the common myna's population attributes such as gene flow, genetic diversity, and effective dispersal, all of which are critical for understanding geographical range expansion of pest species. Results: We found significant genetic structuring across the common myna's Australian distribution, indicating limited levels of effective dispersal amongst the populations founded from historic introductions in the 19th century. The historic introduction points were found to be genetically distinct, such that in the region on the invasion front where admixture did occur, myna populations exhibited higher genetic diversity than in the source populations. Significant isolation by distance was evident amongst populations derived from the same founding population, with genetic diversity decreasing moving away from the point of colonization, and in general, higher levels of gene flow from source to front than vice versa. Main conclusions: This study indicates that despite a 150-year colonization history of mynas in Australia, contemporary genetic structure still largely reflects human-mediated dispersal. However, expanding populations are now connecting and the consequent increased genetic diversity may improve evolutionary potential. These results suggest that more management focus should be directed towards the invasion fronts, rather than the large, historic source populations.