Parasites make hosts more profitable but less available to predators

Abstract

AbstractParasites are omnipresent, and their eco-evolutionary significance has aroused much interest from scientists. Parasites may affect their hosts in many ways by altering host density, vulnerability to predation, and energy content, thus modifying profitability within the optimal foraging framework. Consequently, parasites could impact predator diet and trophic links through food webs. Here, we investigate the consequences of the iridovirus Daphnia iridescent virus 1 (DIV-1) infection on the reproductive success, mortality, appearance, mobility, and biochemical composition of water fleas (Daphnia magna), a widespread freshwater crustacean. We compare search time between infected and uninfectedDaphniapreyed by a common aquatic insect (Notonectasp.) as well as the handling time and feeding preference ofNotonectasp. Our findings show that infection does not change fecundity but reduces lifespan and thereby constrains fitness. InfectedDaphniashow reduced mobility and increased color reflectance in the UV and visible domains, which potentially affects their visibility and thus catchability. Infection increases body size and the amount of proteins but does not affect carbohydrate and lipid contents. Although infectedDaphniahad a longer handling time, they are preferred over uninfected individuals by aquatic insects. Taken together, our findings show that DIV-1 infection could makeDaphniamore profitable to predators (21% energy increase), a positive effect that should be balanced with density reductions due to higher mortalities. We also highlight that exposure to infection in asymptomatic individuals leads to ecological characteristics that differ from both healthy and symptomatic infected individuals.