Genetic variation in Symbiodinium benefit to an octocoral host
When considering evolutionary processes, it is fundamental to consider genetic diversity. While less intuitive, one must also consider diversity when studying ecological processes, as genotypic variation can play a large role in determining ecological outcomes. Algae within the genus Symbiodinium live symbiotically within cnidarian polyps and provide an excellent system to observe the effects of genetic diversity on this mutualistic interaction, particularly in the face of environmental change. The genus Symbiodinium is composed of remarkable taxonomic diversity, both within and among species. We inoculated octocoral polyps (Antillogorgia spp.) with Symbiodinium from two clades, three species, and six genotypes within one species to examine the effect of each strain on polyp performance at both ambient and elevated temperatures.
We found that symbiont strain had a significant effect on polyp performance, measured as growth rate and photosynthetic rate. Different strains also affected the level of nitrogen present in polyp cultures, reflecting differences in interactions strength between these mutualists. The extent to which symbiont strain affected polyp performance was also dependent on temperature, with some strains conferring higher performance at high temperature and other strains conferring higher performance at lower temperature. This suggests that the presence of specific types of Symbiodinium can make a host more or less susceptible to environmental change. Interactions between these species are essential to the productivity of coral reef communities, and the extent to which genetic diversity of symbionts on a reef changes with temperature may have long-term implications for the fitness of hosts in the face of increased ocean temperatures.