Testosterone supplementation in subordinate, small male lizards: consequences for aggressiveness, color development, and parasite load

According to the immunocompetence hypothesis, testosterone stimulatesthe expression of male sexually selected traits while decreasingimmunocompetence. This proposed trade-off was studied by experimentalsupplementation of testosterone to small, subordinate, dull-coloredmale lizards, Psammodromus algirus. Experimental males showeda tendency to overlap their home range with fewer small malesthan did control males and tended to be more aggressive. However,control males were observed more frequently attending femalesthan experimental males. The area of patches of breeding coloration,the number of ticks, and the frequency of recoveries of testosterone-supplementedand control males did not differ significantly. The resultssuggest that small adult males with high levels of testosteronebehave more aggressively, which may be advantageous to securinga breeding territory in the next season. However, the hormonedid not apparently affect ornamentation or parasite load. Weargue that, whatever the mechanisms involved, blocking effectsof testosterone may be adaptive because being cryptic facilitatesa sneaking strategy, and low ectoparasite load may improve survival