Seasonal and spatial influences on gene expression in Antarctic krill Euphausia superba

The high latitudes inhabited by Antarctic krill Euphausia superba Dana are characterised by extreme changes in seasonal conditions, with very low food availability, long periods of darkness and a massive expansion of sea ice in autumn and winter. How krill adapt to these conditions has yet to be determined, and it was the purpose of this study to gain more insight by investigating the differences between summer and winter krill populations at the molecular level. To achieve this, we used a cDNA microarray to compare gene expression between female adult krill caught during summer and winter near the Antarctic Peninsula (60 degrees S), and between Peninsula krill and krill caught near South Georgia (54 degrees S) during the same winter. The Peninsula seasonal comparison showed up-regulation in summer krill of genes involved in feeding and digestion, respiration, motor activity and immunity. Summer krill also showed evidence of increased vitellogenesis, with an insulin-related peptide up-regulated and neuroparsin down-regulated. The comparison between the different overwintering locations showed an up-regulation in the South Georgia krill of genes involved in feeding and digestion, and immunity. There was, however, no differential expression of genes involved in respiration, motor activity or vitellogenesis, suggesting that despite the above differences, both populations of overwintering krill were in a quiescent state. This study shows how krill physiology changes seasonally at the molecular level and how these changes are flexible according to the overwintering environment.