Do sexual differences in life strategies make male lizards more susceptible to parasite infection?

1. Female and male hosts may maximise their fitness by differential evolution of strategies that compensate for the costs of parasite infections. The resulting sexual dimorphism might be apparent in differential relationships between parasite load and body condition, potentially reflecting differences in energy allocation to anti-parasitic defences. For example, male lacertids with high body condition may produce many offspring while being intensely parasitised. In contrast, female lacertids may express a different outcome of the trade-offs between body condition and immunity, aiming to better protect themselves from the harm of parasites.

2. We predicted that females would have fewer parasites than males and a lower body condition across parasitaemia levels, because they would invest resources into parasite defence to mitigate the costs of infection. In contrast, the male strategy to maximise access to females would imply some level of parasite tolerance and, thus, higher parasitaemia.

3. We analysed the relationship between body condition of lizards and parasitaemias of Karyolysus and Schellackia, two genera of blood parasites with different phylogenetic origin, in 565 females and 899 males belonging to 10 species of the Lacertidae (Squamata) that were sampled during a period of 12 years across 34 sampling sites in southwestern Europe.

4. The results concerning the Karyolysus infections were consistent with the predictions, with males having similar body condition across parasitaemia levels even though they had higher infection intensities than females. On the other hand, females with higher levels of Karyolysus parasitaemia had lower body condition. This is consistent with the prediction that different life strategies of male and female lacertids can explain the infection patterns of Karyolysus. In contrast, the parasitaemia of Schellackia was consistently low in both male and female hosts, with no significant effect on body condition of lizards, suggesting that lizards of both sexes maintain this parasite bellow a pathogenic threshold.