Abstract
Parasites have profound fitness effects on their hosts, yet these are often sub-lethal, making them difficult to understand and quantify. A principal sub-lethal mechanism that reduces fitness is parasite-induced increase in energetic costs of specific behaviours, potentially resulting in changes to time and energy budgets. However, quantifying the influence of parasites on these costs has not been undertaken in free-living animals. We used accelerometers to estimate energy expenditure on flying, diving and resting, in relation to a natural gradient of endo-parasite loads in a wild population of European shags Phalacrocorax aristotelis. We found that flight costs were 10% higher in adult females with higher parasite loads and these individuals spent 44% less time flying than females with lower parasite loads. There was no evidence for an effect of parasite load on daily energy expenditure, suggesting the existence of an energy ceiling, with the increase in cost of flight compensated for by a reduction in flight duration. These behaviour specific costs of parasitism will have knock-on effects on reproductive success, if constraints on foraging behaviour detrimentally affect provisioning of young. The findings emphasize the importance of natural parasite loads in shaping the ecology and life-history of their hosts, which can have significant population level consequences.
Highlights
Parasites are among the most successful life forms and infect nearly every known animal taxon [1]
We aim to quantify the costs of endo-parasites by testing three main hypotheses: (H1) parasite load is linked to an increase in the energetic cost of behaviours; (H2) time allocated to affected behaviours is negatively related to parasite load; and (H3) increases in energetic cost of behaviours will be compensated for by changes in time allocation resulting in no link between parasite load and DEE
The best supported model for the effect of parasitism on the cost of flight in females showed a positive relationship between parasite load, with the cost of flight behaviour increasing by approximately 10% from the minimum to maximum parasite load
Summary
Parasites are among the most successful life forms and infect nearly every known animal taxon [1]. [2,3,4]) Such consequences may arise because of multiple costs imposed by parasites, such as immune or stress responses or the direct extraction of resources from their hosts [5,6,7]. These costs are frequently sub-lethal, whereby they alter fitness-related traits, yet these processes are poorly understood because they are challenging to quantify [8]. A principal sub-lethal effect of parasites that can readily be quantified is the impact on performance in terms of movement and foraging This is a critical mechanism since impairment of these behaviours can have substantial negative fitness consequences [9,10]
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