Meeting Abstract
Effective acquisition and management of energetics prior to reproduction should strongly influence reproductive decisions (timing of breeding and reproductive investment). However, because capturing individuals prior to investment is difficult, and because capture often leads to the abandonment of reproduction, we know little about the mechanisms mediating these life-history decisions. We examine physiological parameters predicted to influence energetic management by sampling individuals of a free-living colony of Arctic-nesting common eiders (Somateria molissima) up to three weeks prior to reproduction. We focused on baseline plasma corticosterone (CORT), very-low density lipoprotein (VLDL) and vitellogenin (VTG) for their respective roles in driving daily and annual energetic balance, rate of condition gain (fattening) and follicular investment. We found that baseline CORT increased significantly from arrival to the initiation of reproductive investment (period of rapid follicular growth – RFG), indicating that CORT may stimulate foraging behaviour to facilitate both lipid deposition to females and follicles. Supporting this, we found that plasma VLDL increased throughout the pre-breeding period, peaking as predicted during RFG. Female eiders exhibited unprecedentedly high levels of plasma VTG before their theoretical RFG period, a potential strategy for pre-emptively depositing available protein stores into follicles while females are simultaneously fattening. This study provides some of the first data available examining the temporal dynamics and interaction of the energetic mechanisms driving variation in reproductive decisions and success in diving seaducks.
