Cost of Reproduction and Cost of Parasitism in the Common Lizard, Lacerta vivipara

Parasites may play a complex role in shaping patterns of host reproductive effort and therefore in determining costs of reproduction in their hosts. Parasites may cause a more or less large reduction in the amount of energy an individual host may use for reproduction and maintenance. Irrespective of the parasite-induced reduction in energy intake, infected hosts may either show the same allocation pattern than uninfected hosts, or respond to parasitism by changing the proportion of energy allocated to each trait (e.g. increased investment in current reproduction at the expense of survival). Moreover, hosts may differ in their susceptibility to parasites (e.g. hosts with high reproductive effort may show higher vulnerability to parasite infection). Each of these hypotheses leads to a pattern of correlation between parasite load, host survival and reproduction. In this paper we compared the predicted patterns of correlation between parasite load, host survival and reproduction with those observed for the Lacerta vivipara - haematozoa association. We found that: (1) haematozoa load was positively correlated with lizard reproductive effort; (2) haematozoa load was not correlated with host survival; (3) lizards with high reproductive investment suffered higher mortality rate than lizards with low reproductive investment. These findings suggest that parasites do not significantly reduce host energy intake, and are in agreement with a shift of the allocation rule of parasitized hosts toward reproduction. However, our correlative study does not allow us to attribute this shift to an adaptive host response to parasites rather than a by-product of a differential susceptibility to parasite infections.