THE ROLE OF DISPERSAL ABILITY IN THE PHENOTYPIC DIFFERENTIATION AND PLASTICITY OF 2 MARINE GASTROPODS II - GROWTH

Strategies of response to variation in environmental conditions may de pend upon levels of gene flow among populations, which are commonly re lated to dispersal ability. Local adaptation in immobile species favou rs the adoption of a mosaic of specialist types, while wide dispersal may result in either homogeneity for generalist types or highly flexib le physiologies. The intertidal gastropods Austrocochlea constricta La marck 1822 and Bembicium vittatum Philippi 1846 in Western Australia p rovide suitable subjects for an investigation df these contrasting str ategies, since they co-exist at several widely separated locations in the Houtman Abrolhos Islands and Albany, and have contrasting abilitie s for dispersal. A. constricta is believed to have short-term mobile p lanktonic larvae, while larvae of B. vittatum develop directly within benthic egg masses. Previous study of allozymes suggested greater rest rictions to gene flow in B. vittatum than in A. constricta at both the Abrolhos and Albany, although local disruptions to gene flow were evi dent in A. constricta at the Abrolhos. Despite wider dispersal in A. c onstricta, ranges in growth rates indicated similarly high levels of p henotypic differentiation in this species and B. vittatum across their sympatric distributions in Western Australia. This may be explained b y greater plasticity of growth in A. constricta than in B. vittatum, a s revealed by reciprocal translocation experiments and patterns of tem poral variation in growth. Highest levels of plasticity were recorded in association with the extensive gene flow among populations of A. co nstricta at Albany, while genetic influences on growth were greatest i n B. vittatum at both locations. These results for growth agree with t hose for shape from a previous study of A. constricta and B. vittatum, and suggest that wide dispersal enhances physiological plasticity, an d restricted dispersal local genetic adaptation, but that both mechani sms may produce high levels of phenotypic differentiation. (C) 1998 El sevier Science B.V.