SLOAN, Adrienne J.; WILCOX, Thomas P.: Local Adaptation in Algal Symbionts of Cassiopea xamachana in the Florida Keys

Algal-invertebrate symbioses have been the subject of many genetic, physiological, and biochemical investigations; yet how these associations remain evolutionarily stable continues to be a mystery. Most investigators of endosymbiotic mutualisms assume that all symbionts are equally cooperative. Thus, empirical studies investigating the natural variation among symbiont strains within the same host species are virtually nonexistent. Recent investigations using Cassiopea xamachana and its respective symbiont, Symbiodinium microadriaticum, have revealed that the geographic origin of symbiotic partners critically determines the symbiotic outcome. For example, Cassiopea juveniles infected with algae collected from medusa in close geographic proximity suffered less mortality and higher growth rates than those infected with algae from geographically distant sites. Additional studies using seawater from geographically distant sites to infect Cassiopea juveniles showed similar results. Cassiopea infected with seawater from distant sites suffer greater mortality and lower growth rates than individuals infected with water from their site of origin. Results from these studies suggest that local adaptation influences the evolutionary dynamics of host-symbiont interactions.