Short-term molecular and physiological responses to heat stress in neritic copepods Acartia tonsa and Eurytemora...

Invertebrates inhabiting shallow water habitats represent particularly appropriate organisms for studying the acclimation potential to environmental stress, since they naturally experience large fluctuations in key abiotic factors such as temperature and salinity. We quantified the biochemical- (mRNA transcripts of 78-kDa glucose-regulated protein (grp78), 70-kDa heat shock protein (hsp70), 90-kDa heat shock protein (hsp90), protein synthesis of HSP70) and organismal- (oxygen consumption rates) level responses to acute heat stress on two neritic copepods (Acartia tonsa and Eurytemora affinis) with special emphasis on the role of short-term acclimation. Transcripts of hsp increased with increasing acute temperature exposure and protein quantities (HSP70) were detectable for 30h. In A. tonsa, HSP70 synthesis was also associated with handling stress. In E. affinis, heat-dependent responses were detected in hsp90, grp78 (mRNA) and HSP70 (protein) expression. Acclimation to a warmer temperature significantly decreased the heat stress response in both species. In A. tonsa, short-term acclimation to heat was not detected at the organismal level via metabolic rate. This study reveals interspecific differences in both the gene expression of stress molecules (e.g. hsp90) as well as the stress factors needed to evoke a stress response (heat vs. handling). We demonstrate that cellular stress markers can be useful measures of short-term thermal acclimation in copepods, which may remain undetected by organismal-level measures.