POPULATION GENETICS OF COASTAL AND ESTUARINE INVERTEBRATES: DOES LARVAL BEHAVIOR INFLUENCE POPULATION STRUCTURE?

Abstract

Numerous investigations of the genetic structure of natural populations of marine and estuarine invertebrates suggest that there is generally an inverse correlation between the length of pelagic larval life and the extent to which geographically separated conspecific populations have diverged. There are, however, exceptions to this observation which may be attributed to at least two factors: (1) Natural selection can act to promote divergence of populations even when there is extensive gene flow, and (2) species which appear to have high capacity for dispersal may not always experience high levels of gene flow. In this paper, we point out that even among species with long-lived pelagic larvae there is considerable variation in population structure. Based on limited data, it appears that species that release eggs or weak-swimming larvae into the water column tend to show little population differentiation over broad geographic ranges; in contrast, there is suggestive evidence that species which liberate strong-swimming larvae (e.g., crustaceans) show significant population differentiation. We propose that the behavioral capacities of strong-swimming larvae allow them to exert some control over their dispersal (for example, via depth-regulatory behavior), and that this control limits the passive dispersal which is manifested in species that liberate eggs. Hence, we hypothesize that larval behavior influences population structure in some species of coastal and estuarine invertebrates.