REPRODUCTIVE EFFORT AFFECTS IMMUNE-RESPONSE AND PARASITE INFECTION INA LIZARD - A PHENOTYPIC MANIPULATION USING TESTOSTERONE

Life-history theory predicts that there is a trade-off between reprodu ctive effort and several traits that determine fitness. Infectious dis ease has gained acceptance as a crucial Factor linking both variables. In most instances phenotypic manipulation is necessary to convincingl y demonstrate a causal relationship of reproductive effort on parasiti sm. However, experimental studies that manipulate reproductive effort or parasite load have been rarely conducted in reptiles. In this study , we manipulated reproductive effort of male lizards (Psammodromus alg irus) through testosterone implants, and measured the associated respo nse in some haematological variables and parasite load. Testosterone-s upplemented males had lower scores than control males in factor 1 of a PCA for different blood parameters. This factor is correlated with th e number of white blood cells, especially lymphocytes, and with plasma glucose levels. Experimental males also had higher scores in factor 3 that is mainly related to protein catabolism. Scores of males in comp onent 1 tended to be correlated negatively with tick load, while score s in component 3 were correlated positively with the number of haemogr egarines in the blood. These results suggest that higher investment in reproduction decreases the immune defences, and conduces to the use o f structural resources, which may render individuals more susceptible to some haemoparasites. This is consistent with the idea that an incre ase in reproductive effort mediated by testosterone has a negative eff ect on the ability to counteract parasite infections.