Detecting Genetic Change and Adaptive Variation in Marine Fish: From Empirical Tests to Patterns in the Wild

The classical paradigm of marine fish that inhabit a realm with relatively few natural boundaries, exhibit extremely large effective population sizes, and with a potential for high dispersal, predicts high population connectivity, low genetic differentiation, and slow rates of genetic change. With marked improvements in the design of population genetic sampling programmes and the availability of a plethora of advanced molecular tools enabling direct analysis of ecologically significant divergence across fine spatial and temporal scales, it is evident that the evolutionary world of marine fish deviates frequently from such “open-system – low divergence” models. Increasing evidence of genetic divergence across relatively small spatial scales, sometimes in conjunction with rapid phenotypic and genetic shifts, highlights the potential for local adaptation in marine fish. Importantly, advances in genomic tools, such as transcriptomics, high throughput SNP platforms and next generation sequencing now enable empirical determination of genes under selection and the provision of extensive repositories of sequence information. Such data allows the generation of hypotheses and tests of adaptive dynamics in the field. Here, with reference to genome scans and exploration of candidate genes, we examine how such tools can be integrated with field and laboratory studies to explore the extent and significance of local adaptation in marine fish.