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

Abstract

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 study, 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 of three populations we detected evidence of increased survival in 'home' versus 'away' environments with a Bayesian occupancy model fitted to mark-recapture data. We found support for the 'local' versus 'foreign' criterion of local adaptation as 14 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 kilometres apart on the landscape.

Figure 1.

Apparent annual relative survival from a Bayesian occupancy model fitted to recapture histories of laboratory-born and wild-born juvenile brown trout reciprocally planted into local or foreign natural environments in Newfoundland, Canada. Survival estimates control for the positive effect of body condition (residuals from logged length–weight relationships). Lines represent median survival, boxes capture the 25th and 75th interquartile of the survival estimates, and the whiskers are 1.5 times the interquartile. See table 2 for recapture information.

Figure 2.

Size-adjusted specific growth (percentage change in mass per day) among experimental groups of brown trout reared in three wild environments (Middle Rocky, Rennies, Waterford) and one common-laboratory environment. Data represent 10 000 bootstraps of observed data, where the line represents median growth, boxes capture the 25th and 75th interquartile of the growth estimates, and the whiskers are 1.5 times the interquartile. Note that only the laboratory-born groups were reared in the common-laboratory environment.

Figure 3.

Effect size (log-odds ratio) of local versus foreign performance within environments as a function of spatial distance between populations (e.g. points at the 1000 km scale represent comparisons between populations that have evolved 1000 km apart from each other on the landscape). Grey points are data from figure 2 of Fraser et al. [21], and black points are data from this study. Points above the horizontal line are consistent with local adaptation, whereas points below suggest the opposite.