Evaluation of the introduction history and genetic diversity of a serially introduced fish population in New Zealand

Abstract

Understanding the introduction history and the impact of founder events on invasive species is crucial to understanding the evolutionary mechanisms driving successful invasions. Recently, there has been increased discussion of the ‘‘paradox’’ of invasions, the high success of introduced populations that presumably have limited genetic diversity associated with founder events. The western mosquitofish Gambusia affinis is an ideal species for evaluating this paradox, because it has been widely introduced from its native range in central Texas, USA. This species was introduced to the North Island of New Zealand, circa 1930, and has since invaded aquatic habitats across the North Island. We conducted a microsatellite assay of populations from both the native and introduced range to verify the documented history of invasion and to assess the impact of serial introduction events on the genetic diversity of recently established New Zealand populations. The molecular data were consistent with the documented introduction history. In addition, we found sharp reductions in the allelic richness and the heterozygosity of the introduced populations relative to the original native populations, indicating the presence of founder effects. We also observed the development of strong genetic structure within the introduced range, which is absent within the native range. Finally, we applied approximate Bayesian computation to the introduction scenario to estimate the long-term effective population sizes for the sampled populations.