Meeting Abstract
Complex life cycles characterized by uncertainty at transitions between larval/juvenile and adult environments could favor irreversible physiological plasticity at such transitions. To assess whether thermal tolerance of intertidal mussels (Mytilus californianus) adjusts to post-settlement environmental conditions, we collected juveniles from their thermally buffered microhabitat from high and low-shore locations at cool (exposed) and warm (protected) sites. Juveniles were transplanted to unsheltered cages at the two low sites or common gardened. Juveniles transplanted to the warm site for one month in summer had higher thermal tolerance, regardless of origin site. In contrast, common-gardened juveniles from all sites had lower tolerance indistinguishable from exposed-site transplants. After six months in the field plus a common garden period, there was a trend for higher thermal tolerance at the protected site, while reduced thermal tolerance at both sites indicated seasonal acclimatization. Thermal tolerance and growth rate were inversely related after one but not six months; protected-site transplants were more tolerant but grew more slowly. In contrast to juveniles, adults from the low-shore exposed and protected sites retained differences in thermal tolerance after one month of common gardening in summer. Both irreversible and reversible forms of plasticity must be considered in organismal responses to changing environments.
