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Testosterone, body size, and sexual signals predict parasite load in Yarrow’s Spiny Lizards (Sceloporusjarrovii)

Halliday, W.D., Paterson, J.E., Patterson, L.D., Cooke, S.J., Blouin-Demers, G.
Canadian journal of zoology 2014 v.92 no.12 pp. 1075-1082
Sceloporus, aggression, body size, ectoparasites, glucocorticoids, head, immunocompetence, lizards, locomotion, males, parasite load, surface area, testosterone, Arizona
Parasite load significantly impacts host health and fitness and may vary substantially among individuals within a population. The immunocompetence handicap hypothesis posits that sexual signals are honest indicators of male quality because they are maintained by testosterone, an immunosuppressant that yields higher parasite loads. Additionally, testosterone may influence parasite load by increasing activity levels. We examined these two hypotheses in a wild population of Yarrow’s Spiny Lizards (Sceloporus jarrovii Cope, 1875) in Arizona. We (i) compared fecal testosterone levels to ectoparasite and haemoparasite loads, (ii) tested if sexual signals (total coloured area, aggression, and head size), locomotor activity, and body size correlated with testosterone levels, and (iii) compared sexual signals, locomotor activity, and body size to parasite load. Ectoparasite loads increased with total coloured area and tended to increase with testosterone, but this latter relationship was only nearly significant. Parasite loads increased with body size. Thus, we found some support for the immunocompetence handicap hypothesis and none for the activity hypothesis. Our results are consistent with an alternative hypothesis that larger individuals have more parasites because they have more surface area and (or) have had longer to accumulate parasites. Future studies should examine the relative contributions of testosterone and glucocorticoids in driving variation in parasite loads.