Are trait differentiation and genetic relatedness correlated in eelgrass genotypes, and can relatedness be used to predict the outcome of intraspecific interactions?

Background/Question/Methods

Biodiversity and ecosystem function are often linked because species richness is correlated with the functional trait diversity of the community, which in turn affects the productivity and stability of the community through niche partitioning and complementarity. However, species richness is a crude metric of functional diversity, and recently there has been an increased interest in using phylogenetic distance as a proxy for ecological trait distance. While the same principles should apply at the population level with interacting individuals of the same species, few studies have explored using genetic relatedness as a proxy for trait differentiation within species. Here we explicitly test the relationship between genetic relatedness and trait distance using 41 eelgrass (Zostera marina) genotypes. We measured traits related to nutrient uptake, morphology, biomass and growth, photosynthesis, and chemical defences for all genotypes. We used these trait measurements to calculate a multivariate pairwise trait distance for all possible genotype combinations. We then examined the relationship between trait distance and pairwise relatedness estimated from 11 microsatellite markers.  Furthermore, we examined the effects of relatedness on the performance of assemblages of eelgrass genotypes grown in the field.  We planted assemblages of genotypes with low, mid, and high average relatedness in Bodega Harbor, CA using the 41 genotypes used for trait measurements.

Results/Conclusions

Surprisingly, we found no evidence of a significant correlation between genetic relatedness and multivariate trait distance. This pattern was true for individual traits as well, where most traits showed no correlation between relatedness and trait distance and a few traits showed a weak, non-significant correlation with relatedness, although not in the same direction (i.e. both positive and negative correlations).  However, preliminary results from the field experiment suggest that there is a unimodal relationship between relatedness and performance, where assemblages of high and low relatedness tend to perform better than assemblages of mid level relatedness. Our work suggests that while relatedness may be a poor proxy for trait differentiation between genotypes, it may still influence intraspecific interactions.