Effects of temperature shifts on life parameters and expression of fatty acid synthesis and heat shock protein genes in temperate and Antarctic copepods Tigriopus japonicus and Tigriopus kingsejongensis

Abstract

Global warming, increase of the atmospheric temperature leading to changes in climate, is a growing environmental concern for all organisms including marine organisms, and many efforts have been made to reveal the potential adverse effects on the systematics of aquatic organisms in response to the temperature changes. To examine the effects of temperature shifts on copepods in temperate and polar regions, we compared the life parameters and gene expression profiles of the de novo lipogenesis (DNL) pathway and heat shock protein (hsp) genes in the temperate copepod Tigriopus japonicus (T. japonicus) and the Antarctic copepod Tigriopus kingsejongensis (T. kingsejongensis). The median lethal temperature (LT50) and no observed effect level (NOEL) in the temperate copepod T. japonicus were determined to be 35.3 and 32 degrees C, respectively, in response to a temperature increase of 2 degrees C a day. In the Antarctic copepod T. kingsejongensis, the LT50 and NOEL were determined to be 24.8 and 12 degrees C, respectively. In addition, delayed developmental time and impaired fecundity were observed (P<0.05) in response to temperature changes in T. japonicus. T. japonicus DNL pathway genes were down-regulated in response to high temperature, whereas T. kingsejongensis DNL pathway genes showed up-regulation in response to high temperature, indicating that these two Tigriopus species have different modes of action in response to temperature shifts. In both copepods, transcription of heat shock proteins (hsps) was mostly up-regulated in response to temperature shifts, but it showed moderate expression at 15 degrees C for T. japonicus and 4 degrees C for T. kingsejongensis. These findings indicate temperature shift-mediated species-specific modulations of the DNL pathway and hsps gene expression, leading to alteration of lipid synthesis and chaperoning with deleterious effects on the life parameters of these two copepods.