Ecological limits can obscure expansion history: patterns of genetic diversity in a temperate mosquito in Hawaii

Abstract

Because biological invasions can be swift and are rarely examined immediately and/or followed over time, spatial genetic diversity analyses grounded in a well-developed body of theory are often used to reconstruct historical patterns of expansion. Unfortunately, the role of selection in shaping and potentially disrupting such reconstructions has seldom been examined. The mosquito Aedes japonicus japonicus is a temperate, cold-adapted species native to northern Japan that has recently established populations on the island of Hawaii. We used variation at seven microsatellite loci and one mitochondrial locus to examine Hawaiian populations collected in 2004, shortly after its first detection, and then in 2010–2011. Samples were collected along an elevational/temperature gradient, ranging from sea level to 1,200 m. Specimens collected near sea level in 2004 from the earliest detected population exhibited high genetic diversity. Contrary to expectations that diversity would decrease outward from the point of introduction, in 2010–2011 high elevation populations had the greatest genetic diversity, while low elevation populations (including those with high diversity in 2004) now had lower diversity and were significantly differentiated from each other, suggesting severe bottlenecks. We hypothesize that differential survival across temperatures at high versus low elevations has subverted the expected genetic signature of an expanding population.