The role of parasitism in the energy management of a free-ranging bird.

Olivia Hicks,Mark Newell,Jonathan A Green,Francis Daunt,Charline Parenteau,Sarah J Burthe,Olivier Chastel

doi:10.1242/jeb.190066

Abstract

ABSTRACTParasites often prompt sub-lethal costs to their hosts by eliciting immune responses. These costs can be hard to quantify but are crucial to our understanding of the host's ecology. Energy is a fundamental currency to quantify these costs, as energetic trade-offs often exist between key fitness-related processes. Daily energy expenditure (DEE) comprises of resting metabolic rate (RMR) and energy available for activity, which are linked via the energy management strategy of an organism. Parasitism may play a role in the balance between self-maintenance and activity, as immune costs can be expressed in elevated RMR. Therefore, understanding energy use in the presence of parasitism enables mechanistic elucidation of potential parasite costs. Using a gradient of natural parasite load and proxies for RMR and DEE in a wild population of breeding European shags (Phalacrocorax aristotelis), we tested the effect of parasitism on maintenance costs as well as the relationship between proxies for RMR and DEE. We found a positive relationship between parasite load and our RMR proxy in females but not males, and no relationship between proxies for RMR and DEE. This provides evidence for increased maintenance costs in individuals with higher parasite loads and suggests the use of an allocation energy management strategy, whereby an increase to RMR creates restrictions on energy allocation to other activities. This is likely to have fitness consequences as energy allocated to immunity is traded off against reproduction. Our findings demonstrate that understanding energy management strategies alongside fitness drivers is central to understanding the mechanisms by which these drivers influence individual fitness.

Highlights

Parasites cause major fitness consequences to a huge array of taxa (Booth et al, 1993; Gooderham and Schulte-Hostedde, 2011; Reed et al, 2008)
We investigate two questions: (1) Does parasite load relate to resting metabolic rate (RMR)? We expect that individuals with higher parasite loads will have higher immune costs and that this will be reflected in elevated RMR. (2) Does Daily energy expenditure (DEE) relate to RMR and what can this tell us about the allocation between energy to reproduction and self-maintenance of this species? We predict that individuals will be energetically constrained by rapidly growing chicks during the chick-rearing period under the allocation model and any increase in RMR will not result in an increase in DEE
When year and brood age are accounted for, T3 concentration increased by 150% across the range of natural parasite load

Summary

Introduction

Parasites cause major fitness consequences to a huge array of taxa (Booth et al, 1993; Gooderham and Schulte-Hostedde, 2011; Reed et al, 2008). Parasites prompt sub-lethal effects to the host by eliciting immune or stress responses Ignoring these effects of parasites reduces our understanding of their host’s ecology, as we know that parasites can drive a large array of fitness-related traits (Boulinier et al, 2016; Hamilton and Zuk, 1982; Norris and Evans, 2000; Reed et al, 2008; Sheldon and Verhulst, 1996)

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