Fine-scale local adaptation in an invasive freshwater fish has evolved in contemporary time

Adaptive evolutionary change in only a few generations can increase the ability of non-native invasive species to spread, and yet adaptive divergence is rarely assessed in recently established populations. In this paper, we experimentally test for evidence of fine-scale local adaptation in juvenile survival and growth among three populations of an invasive freshwater fish with reciprocal transplants and common-garden experiments. Despite intrinsic differences in habitat quality, in two out of three populations we detected evidence of increased survival in ‘home’ vs. ‘away’ environments with a Bayesian occupancy model fitted to mark-recapture data. We found support for the ‘local vs. foreign’ criterion of local adaptation as 14 out of 15 pairwise comparisons of performance were consistent with local adaptation (p < 0.001). Patterns in growth were less clear, though we detected evidence of location and population-level effects. Although the agents of divergent ecological selection are not known in this system, our results combine to indicate that adaptive divergence – reflected by higher relative survival of local individuals – can occur in a small number of generations and only a few kilometers apart on the landscape.