Fidelity and flexibility in coral symbioses

Abstract

Understanding whether or not corals have the flexibility to change their compliment of symbionts to acclimate to global warming is an important goal in reef ecology. While host fidelity to a single clade of symbiont is the dominant pattern in present day corals, current estimates of flexibility are unreliable because few studies have measured it rigorously and with adequately sensitive genetic techniques. Furthermore, flexibility must be explored at the level of the subclade because generalisations of physiological performance among clades of Symbiodinium are not valid. In addition, we should not necessarily expect to see shifts among symbionts without distinct and enduring changes in environmental conditions. The few biogeographical comparisons available suggest that when corals encounter a novel environment they have the flexibility to change symbionts. Flexibility in the acquisition of symbionts is common at the time of infection, which in most corals occurs during, or shortly after, settlement. Consequently, flexibility may be a feature of the life history of all species that reacquire symbionts each generation.