Key points are not available for this paper at this time.
Gene exchange among widely separated areas characterizes many marine organisms with planktonic dispersal. From an evolutionary perspective, the essential feature of such dispersal is that recruits to local populations come from somewhere else. Thus, localized adaptation is not accumulated over time, and changes in the genetic composition of adults reflect single-generation effects of selection and recruitment. The most obvious effect of planktonic dispersal is the reduction of geographic variation in genetic composition (e.g., Scheltema, 1971, 1978), and low variances of allelic frequencies have been found to be associated with planktonic dispersal (e.g., Berger, 1973; Levinton and Suchanek, 1978; Winans,
Johnson et al. (Thu,) studied this question.