Abstract
Sexual reproduction imposes risks on participating adults through increased probability of injury, predation pressure, or parasite exposure. Evolutionary theory predicts that animals will tolerate parasite infection during reproduction at the expense of increased parasite load, resulting in individual trade-offs between the temporary costs of current reproduction against the long-term evolutionary benefits in the form of life-long production of viable offspring. We tested this hypothesis, predicting that participation in sexual reproduction increases parasite exposure by investigating ectoparasite load on sand lizards (Lacerta agilis). Using generalized additive models to correct for bimodal seasonal dynamics of ectoparasite activity, site and year, we found that ectoparasite load is higher in adults (animals that overwintered at least twice) than in subadults that overwintered once only. Between sexes of adult sand lizards, males had a higher number of blood-sucking ectoparasites than females. Our results indicate that both sexually-motivated extensive locomotion associated with territory defence and mate search in males, and increased energy uptake during gestation in females, contribute to elevated ectoparasite exposure. Increased host mobility associated with increased ectoparasite exposure leads to collateral burden of reproduction on sand lizard populations.
Highlights
We studied sand lizards (Lacerta agilis) in orchards in Central Europe to investigate how sexual maturity and behaviour associated with reproduction influenced ectoparasite exposure
Our simulation study showed that increased host mobility can increase ectoparasite exposure
In the simplified scenario with evenly distributed ectoparasites and a random walk of hosts, we observed an increase of ectoparasite exposure in hosts that covered longer distances (Fig. 1)
Summary
In addition to investing resources in maintenance and reproduction, the infected host must mount defence against the parasite, and repair damage suffered (McNew et al 2020). The resulting cumulative energetic requirements may exceed the individuals’ capabilities, imposing a trade-off between the health and reproduction of the host. By defending against a parasite and coping with the damage incurred hosts are predicted to increase their probability of survival and future reproduction. Whether the infected host invests resources into growth or reproduction instead of defence and repair depends on its recent vs future reproductive prospects (Sorci et al 1996, Agnew et al 2000). When current reproduction is unlikely, such as when experimental individuals are kept in separated housing, infected animals reduce their
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