Evolutionary ecology: how to reconcile pelagic dispersal with local adaptation
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Because of dispersal, many marine organisms exist in a series of local populations spanning a wide variety of different physical environments. Recruitment is often sporadic, and thus the age structure and density of the population are also highly unpredictable. Rates of gene flow may be high, and this can inhibit local genetic differentiation. How can local adaptation occur when the environments that young or adults will face are so variable and unpredictable? One solution is phenotypic plasticity, a set of specific responses to cues in the environment that indicate local conditions critical to fitness. In some cases local populations may be very finely tuned to the local environment. Other environmental factors simply cannot be predicted by adults. For such cases, fixed responses are the best solution, averaged over the dispersed range of the species. Such fixed responses may be highly maladaptive at many local levels. Their validity cannot be interpreted in studies that restrict themselves to a few localities. The relative roles of local genetic differentiation, phenotypic plasticity, and large-scale fixed responses in determining behavior and morphology should be a function of the selective regime, the degree of larval dispersal (and hence the gene flow among populations), and the detection abilities of the benthic individuals. Phenotypic plasticity may most likely occur in species with widely dispersed larvae and good sensory capabilities. In contrast, corals may employ a strategy of simply varying the phenotypes of their young, as do some plant species.