Authors

A Hayward¹;  ¹ University of Stirling

Discussion

A cornerstone of life-history theory is that phenotypic variation may be created and maintained by trade-offs. Experimental studies show that increased investment in reproduction is traded-off with increased parasite burden. Such observations have been ascribed to hormonal changes during reproduction and their interactions with immunity, but collecting data on reproduction, parasite-specific immunity and hormones in wild animals is challenging. Wild St Kilda Soay sheep have been intensively studied for over 30 years and face infection with gastrointestinal strongyle nematodes. Recent work has shown that females reproducing in spring have reduced antibody concentrations in the summer. To further investigate this reproduction-immunity trade-off, I repeatedly collected faecal samples from female Soay sheep during pregnancy and lactation. Samples were analysed for strongyle faecal egg counts (FEC), strongyle-specific antibody concentrations, and hormone concentrations. I will show that between-individual differences explain a large proportion of the variation in these traits and that faecal antibodies represent an effective marker of strongyle resistance. I will examine changes in FEC and antibody concentrations across the lambing season, and identify the role of reproductive investment and between-individual variation in governing these changes. Finally, I will show how changes in hormone concentrations are linked to reproductive traits and antibody production.