Print PageIntra-specific trait variation in habitat-forming species can have important ecological consequences at the population, community, and ecosystem level. However, the contribution of genetic variation among individuals to these effects is seldom documented, leaving it an open question whether overall trait variation results primarily from differences within or among genotypes. We quantified morphological and physiological variation within and among genotypes of a marine foundation species, the clonal seagrass Zostera marina, across several experiments in the laboratory and field both with and without competition. We also examined the potential for trade-offs among traits across genotypes, as well as among individuals of a given genotype. Finally, we assessed whether trait variation is correlated with the number of alleles shared between individuals to determine if relatedness can be used as a proxy for variation in key morphological and physiological traits.
Results/Conclusions
We found that genotypes differed in shoot production, biomass, allocation to sexual reproduction, and both root and shoot nutrient uptake rates. These differences were consistent in both laboratory and field experiments, regardless of the presence or absence of intra-specific competition. Zostera genotypes also differed with respect to the community of invertebrates that are closely associated with the plants: for instance, the opisthobranch gastropod Phyllaplysia taylori differentiated among genotypes in a mesocosm experiment, preferentially laying egg sacs on particular genotypes. Bivariate comparisons of traits across genotypes revealed strong positive correlations between some morphological variables (e.g., above-ground biomass and maximum root length) and a negative relationship between leaf nitrate uptake and root ammonium uptake. However, bivariate trait comparisons within individuals of the same genotype did not show the same patterns as across genotypes. The relationship between trait variation among genotypes and the relatedness of those genotypes measured at neutral markers varied in strength and sign across traits. Interestingly, relatedness proved a more consistent predictor of mixture performance than direct measures of trait variation. Our results suggest that morphological variability observed in seagrasses results primarily from variation among, rather than within, genotypes. Thus, differential loss of particular genotypes to disturbance could result in significant changes in trait variation, with resulting population- and community-level effects.
