Genomic approaches to detecting thermal stress in Calanus finmarchicus (Copepoda: Calanoida)

Abstract

Zooplankton may be subjected to physiological stress as they encounter rapid and large changes in temperature through vertical migration or transfer into different water masses. Induction of one or more heat shock proteins (hsp) is a common protective response to thermal stress in organisms. We looked for evidence for such a response in Calanus finmarchicus. We compared hsp70 expression in copepods exposed to temperature stress with that for non-stressed controls. Partial sequences of the amplified cDNA product were obtained and aligned with known hsp70 sequences to establish the identity of the heat shock protein. In one experiment, animals were transferred from their collection temperature (8 °C) to 20 °C for 30 min, and then returned to 8 °C for 4 h before sampling for gene expression levels. In another, the animals were exposed to 18 °C over 48 h before sampling for molecular analysis. A four-fold induction of hsp70 was measured in both groups of heat shocked animals using quantitative real time polymerase chain reaction (PCR). The experimental temperatures, although high for C. finmarchicus, are within the range of temperatures experienced by this species in their habitat. In addition to confirming an hsp70-mediated response in C. finmarchicus, the findings suggest that a recent history of thermal stress may be assessed in natural populations through a routine molecular assay.