Population genetic consequences of larval dispersal mode and hydrography: a case study with bryozoans

Genetic analysis of the marine bryozoans Celleporella hyalina and Electra p ilosa using the RAPD technique revealed population structuring correspondin g to the contrasting modes of larval dispersal. Samples of C. hyalina exhib ited genetic differentiation over distances as small as 10 m, concordant wi th the limited dispersal predicted by a simulation model, based on the shor t pelagic phase of the lecithotrophic larvae and the local hydrography. In contrast, E. pilosa showed high levels of genetic heterogeneity only over m uch larger spatial scales, commensurate with its production of comparativel y long-lived planktotrophic larvae. The population differentiation observed between samples of E. pilosa, collected from sites 70 km apart, is reconci lable with coastal water currents and frontal systems that restrict the exc hange of water masses between the two sites. Hydrographic conditions and di scontinuous distribution of suitable substrata therefore are seen to constr ain gene flow, creating opportunities for local genetic differentiation des pite the high dispersal potential of pelagic larvae.