Population differentiation in the life-history characterisitcs of salt-marsh annuals

Davy, A.; Smith, H.

Coastal salt marshes are heterogeneous spatially but predictable temporally. Genetic differentiaton between populations on different parts of a marsh in response to this combination of circumstances is well documented in several perennial species; differentiation is evident in certain features of the life cycle that contribute to overall fitness. There are distinct populations of annuals in the marshes of the north Norfolk coast of Britain that have particular micro-habitats and different vegetational affinities, within the annual species Suaeda maritima and within the complex of several closely related species of Salicornia. Consequently, 3 sequential questions about these annuals may be posed: what is the extent of genetic differentiation? Can any of this variation be demonstrated to have adaptive value? Evidence for the upper- and lower-marsh populations of (diploid) Salicornia europaea agg. at Stiffkey, UK is reviewed. The 6 main approaches described are collateral cultivation, perturbation of the field environment, isozyme analysis and 3 types of reciprocal transplantation. The value of these complementary methods is discussed,and they are used to demonstrate considerable genetic differentiation between the 2 populations; it is manifested in the phenology of growth, mortality and density-dependent fecundity. In terms of the ability of individuals to leave descendants, there is a dramatic reduction in fitness of each population when it is grown in the reciprocal environment. This finding indicates that the genetic differentiation has clear adaptive value.

Population differentiation in the life-history characterisitcs of salt-marsh annuals

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