Meeting Abstract
To determine whether thermal tolerance in the mussel Mytilus californianus is genetically determined or whether juveniles adjust to their environment through phenotypic plasticity, we analyzed acute thermal stress tolerance and growth rates of common-garden acclimated and reciprocally transplanted mussel recruits. Juvenile mussels were collected from two low intertidal sites at Hopkins Marine Station in central California, wave-protected (warm) and wave-exposed (cool). One group was immediately exposed to an acute heat ramp to 35.8, 37.7, or 38.6°C in air to determine baseline heat tolerance. A second group was placed in a common garden for one month before exposure to the same acute heat ramps. The remaining mussels were reciprocally relocated to the origin field sites for one month and then subjected to heat stress. These treatments were repeated for two high intertidal sites from protected and exposed locations. Although not significant, there was a trend for greater baseline thermal tolerance in juveniles from the protected site. After one month, juveniles outplanted to the protected site exhibited higher survival following thermal stress, regardless of the origin site. Thermal tolerance and growth rate were inversely correlated; mussels from all origin sites were more thermally tolerant but grew more slowly at the protected location. Both origin site and outplant location significantly influenced growth rate. There was also a significant interaction between origin and outplant site – high-site juvenile mussels grew faster than low-site mussels when placed at the exposed site, but low-site mussels grew faster at the protected site. Our results imply substantial, environmentally driven plasticity in both thermal tolerance and growth rate among recent mussel recruits.
