Distinct behavioral patterns across a non-native population of Gambusia affinis

In many species experiencing range expansion resulting from human activity, individuals at the range boundary may be phenotypically distinct from individuals of that species living in longer-established parts of their range. Despite a handful of cases suggesting these differences occur, little is known about how widespread this variation is across diverse invasive species, or whether and how such variation might facilitate the success of introduced species. In the present study, we identified subpopulations of the western mosquitofish, Gambusia affinis, in the lower Susquehanna River watershed in the eastern United States. We collected fish from three sites believed to differ in the time since their establishment. We introduced these fish to a series of behavioral tests on them to investigate variation in exploratory behavior, boldness, activity level, and sociality to determine 1) whether these subpopulations differed in these behaviors, 2) whether variation in any of these behaviors correlated with one another, and 3) whether subpopulations may differ in variation in these correlated behaviors. We found that fish collected from the longest established subpopulation were more active than fish in more recently established subpopulations. We found that high boldness, activity levels, and sociality correlated across subpopulations, but did not differ between them. Collectively, our results indicate that while subpopulations do differ in one behavioral measure, we did not find evidence of variation in correlated behaviors depending on the estimated time since establishment.