THE USE OF GENETIC CLINES TO ESTIMATE DISPERSAL DISTANCES OF MARINE LARVAE.

Many unresolved issues in the ecology and evolution of marine populations center on how far planktonic larvae disperse away from their parents. Genetic tools provide a promising way to define the spatial spread of larvae, yet their accurate interpretation depends on the extent to which genetic loci are under selection. Genetic dines, geographic zones in which genetically differentiated populations interbreed, provide opportunities to explicitly and simultaneously quantify the relative roles of selection and dispersal. Here, we review the theory and analysis of genetic dines and apply these techniques to published studies of multilocus dines in the sea. The geographic width of a stable genetic dine is determined by a balance between the homogenizing effects of dispersal and the diversifying effects of selection. For marine researchers, the power of genetic dines is that, if selection and clinal width are quantified, then the average geographic distances that larvae move can be inferred. Measuring selection or dispersal through laboratory or field-based experimentation, is possible, though logistically difficult, for pelagically dispersed organisms. Instead, dispersal may be more robustly quantified from the degree of linkage disequilibrium between two or more loci, because linkage disequilibrium integrates selection across multiple life stages and generations. It is also relatively insensitive to whether exogenous or endogenous selection operates. Even without quantifying linkage disequilibrium, the theory of genetic dines indicates that the average dispersal distance of larvae is a fraction (i.e., generally <35%) of the clinal width. Because dine theory is based on several underlying assumptions, including near-equilibrium between selection and migration, the dispersal distances inferred from empirical data should be of the correct order but may not be precise. Even so, such estimates of larval dispersal are valuable, as they can be utilized to design appropriate scales for future investigations and provide some guidance to conservation efforts. [ABSTRACT FROM AUTHOR]