Changes in gene expression, lipid class and fatty acid composition associated with diapause in the marine copepod Calanus finmarchicus from Loch Etive, Scotland.

Abstract

Zooplankton are the major primary consumers in pelagic ecosystems, providing the principal pathway for energy transfer from primary production to higher trophic levels. The marine copepod Calanus finmarchicus is an important component of the pelagic food web in the North Atlantic and peripheral ecosystems, and forms an essential dietary component of a number of commercially important fish. As part of its life cycle, many C. finmarchicus overwinter in a diapause phase (a dormant overwintering phase where development is suppressed in adaptation to the seasonal food supply) at depths of 500 to 2000 m, but little is known about the triggers that initiate and terminate diapause, or the internal processes associated with these triggers. Understanding these processes is important, given that subtle changes in the environmental conditions which may affect diapause could have consequences for the entire Calanus-based ecosystem. In this study I took advantage of relatively easy access to a deep (> 100 m), isolated population of C. finmarchicus in Loch Etive (a sea loch on the west coast of Scotland) to sample Calanus finmarchicus monthly between April 2006 and June 2007 and measure lipid dynamics and gene expression associated with diapause. Chapter 1 of this thesis provides a general introduction to diapause and Calanus finmarchicus, Chapter 2 reports on the population of C. finmarchicus in Loch Etive, Chapter 3 reports changes in the lipid class and fatty acid composition of individual copepods, Chapter 4 reports on differential gene expression between diapausing and active C. finmarchicus and Chapter 5 provides a general discussion and puts this research into context. This study provides some initial insight into possible gene expression patterns, but further work is needed to attribute specific gene expression patterns with initiation and termination of diapause.