Meeting Abstract

LBS4.4  Sunday, Jan. 6  Rapid evolution across independent invasions into novel environments LEE, Carol Eunmi; University of Wisconsin, Madison carollee@wisc.edu

A fundamental unresolved problem in ecology and evolution regards the limits to species distributions. Invasive species provide powerful models for studying limits to species distributions and factors that allow those distributions to shift. Of the large number of species that are introduced into novel habitats, few become successful as invaders. What allows some species to invade, when most cannot? We hypothesized that invasions into novel environments might involve the rapid and parallel evolution of genetically labile traits. Within the past century, the copepod Eurytemora affinis has invaded freshwater habitats multiple times independently from saline sources. To dissect evolutionary responses during these independent habitat invasions, we integrated analyses of physiological function (ion efflux and uptake) with comparative functional genomics (using custom cDNA microarrays). We analyzed evolutionary shifts during invasions for pairs of saline ancestral source and derived freshwater populations across four independent invasions from two genetically distinct clades. We found evolutionary shifts in the expression of genes spanning many functional categories, including osmoregulation and stress response. A diverse array of genes showed parallel shifts in gene expression across multiple independent invasions, while some genes showed parallelism only within clades. In particular, shifts in gene expression and physiological function suggested mechanisms to reduce ionic loss rather than to increase ion uptake in the derived freshwater populations. The integration of functional (physiological) and gene expression analyses has allowed us to prioritize plausible candidate genes that might serve as the targets of selection. The evolutionary parallelism observed here might have relevance for taxonomically different but ecologically similar species that invade across similar habitat clines.