Some communities, such as coral reefs, kelp forests, and seagrass beds may be comprised of a single dominant species, and genetic diversity within these species may play an analogous role to species diversity in more speciose systems. Genetic diversity is high in many Zostera populations (as many as 15 genotypes per square meter) and small scale genetic structure can be strong and patterns are consistent on decadal time scales. Through manipulative field experiments and laboratory mesocosms, we have been examining the effects of genetic diversity in the eelgrass Zostera marina on community function and stability. Field experiments show that genetic diversity enhances community resistance to natural disturbances by grazing geese and algal blooms as well as experimentally imposed disturbances. These differences in disturbance response affect the abundance of epifaunal grazers such as amphipods and other small crustaceans on seagrasses. In addition, longer term experiments show that as grass density reaches natural levels, we find consistent positive effects of genotypic richness on diversity (Hughes and Stachowicz 2011).
In laboratory experiments we have been measuring the physiological performance of individual seagrass clones grown in common gardens. We find strong physiological differences in nutrient uptake, grazer resistance, and growth rate as well as allocation to shoot vs. root biomass in which no single clone maximizes all aspects of clonal performance. This suggests there are phenotypic differences among clones that may underlie observed diversity effects in the field (Hughes et al. 2009; Tomas et al. 2011).
Our current work in this area focuses on understanding the influence of genetic relatedness, trait differences, and genotypic identity on seagrass ecosystem functioning. Field experiments show independent effects of trait diversity and relatedness on eelgrass performance (Abbott and Stachowicz 2016, Abbott et al. 2017) such that high trait diversity enhances performance while relatedness decreases performance. Despite some early results to the contrary (Stachowicz et al. 2013), we have not been able to consistently use genetic relatedness at neutral markers to predict ecological similarity (Abbott et al. 2018). We are now using genomic resequencing of plants from around the world and common gardens to get at the basis of the functional variation among Zostera genotypes with the hope that ultimately genomic variation might be usable as a consistent proxy for trait diversity. This also involves studies of local and global scale adaptation of eelgrass, especially to both regional and inter-annual variation in thermal regime, including responses to extreme warming events. These experiments use a combination of field observations, reciprocal transplants, common gardens and genomic associations and will be an increasing focus of the lab moving forward. The project summary of our recently funded NSF grant on this topic can be found here.
Abbott, JM, K Dubois, RK Grosberg, SL Williams and JJ Stachowicz. 2018.Genetic distance predicts trait differentiation at the subpopulation but not the individual level in eelgrass, Zostera marina. Ecology and Evolution DOI: 10.1002/ece3.4260 [-pdf-]
Abbott, J.M., S.L. Williams, R.K. Grosberg, and J.J. Stachowicz. 2017. Multiple dimensions of intraspecific diversity affect biomass of eelgrass and its associated community. Ecology 98: 3152–3164 [-pdf-]
Reynolds, L.K., K. DuBois, J.M. Abbott, S.L. Williams, and J.J. Stachowicz. 2016. Response of a Habitat-Forming Marine Plant to a Simulated Warming Event is Delayed, Genotype Specific, and Varies with Phenology. PLoS ONE 11 (6), e0154532.[-pdf-]
Abbott, J.M. and J.J. Stachowicz. 2016. The relative importance of trait vs. genetic differentiation for the outcome of interactions among plant genotypes. Ecology 97: 84-94.[-pdf-]
Stachowicz, J.J., S.J. Kamel, A.R. Hughes, and R.K. Grosberg. 2013. Genetic relatedness influences plant biomass accumulation in eelgrass (Zostera marina). American Naturalist. 181:715-724[-pdf-]
Kamel, S.J., A.R. Hughes, R.K. Grosberg, and J.J. Stachowicz. 2012. Fine-scale genetic structure and relatedness in the eelgrass Zostera marina. Marine Ecology Progress Series 447:127-137[-pdf-]
Tomas F., J.M. Abbott, M. Balk, C. Steinberg, S.L. Williams, and J.J. Stachowicz. 2011. Plant genotype and nitrogen loading influence seagrass productivity, biochemistry, and plant-herbivore interactions. Ecology 92:1807-1817[-pdf-]
Hughes, A.R. and J.J. Stachowicz. 2011. Seagrass genotypic diversity increases disturbance response via complementarity and dominance. Journal of Ecology 99:445-453.[-pdf-]
Hughes, A.R., R.J. Best, and J.J. Stachowicz. 2010. Genotypic diversity and grazer identity interactively influence seagrass and grazer biomass. Marine Ecology Progress Series 403: 43-51. [-pdf-]
Hughes, A.R., J.J. Stachowicz, and S.L. Williams. 2009. Morphological and physiological variation among seagrass (Zostera marina) genotypes. Oecologia 159:725-733.[-pdf-]
Hughes, A.R. and J.J. Stachowicz. 2009. Ecological impacts of genotypic diversity in the clonal seagrass, Zostera marina. Ecology 90: 1412-1419.[-pdf-]
Hughes, A. R., and J. J. Stachowicz. 2004. Genetic diversity enhances the resistance of a seagrass ecosystem to disturbance. Proceedings of the National Academy of Sciences of the United States of America 101:8998-9002. [-pdf-]