Increased mite parasitism as a cost of testosterone in male striped plateau lizards Sceloporus virgatus
Authors: COX, ROBERT M.; JOHN-ALDER, HENRY B.
Source: Functional Ecology, Volume 21, Number 2, April 2007 , pp. 327-334(8)
Publisher: Blackwell Publishing
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Abstract:
Summary • Testosterone (T) co-ordinates the seasonal and sex-specific expression of numerous physiological, behavioural and morphological traits that contribute to male reproductive success. However, increased susceptibility to parasitism has been proposed as a potential cost of elevated plasma T. • During the spring breeding season, male striped plateau lizards Sceloporus virgatus harbour significantly more ectoparasitic mite larvae (Acari: Trombiculidae) than females. Plasma T levels are also elevated in males at this time, suggesting that sex differences in mite parasitism may be driven by underlying sex differences in circulating T. • We tested this hypothesis experimentally by manipulating plasma T levels of yearling males via surgical castration and exogenous T implants. Upon recapture of free-living animals, we found significantly fewer mites on castrated males relative to either intact controls or castrated males that received T implants. • After removing variance attributable to treatment effects, we observed (1) a positive correlation between residual measures of plasma T and mite load, and (2) a negative correlation between residual measures of mite load and growth rate. These correlations suggest a growth cost associated with mite parasitism. • Previous studies have shown that exogenous T increases parasitism, but ours is one of the few to show that castration also reduces parasitism. This result, coupled with the fact that our induced plasma T levels remain within physiological limits, makes this one of the clearest demonstrations of a functional relationship between T and parasitism in any free-living vertebrate. Functional Ecology (2007) 21, 327-334 doi: 10.1111/j.1365-2435.2007.01251.xKeywords: castration; cost of reproduction; growth rate; immunocompetence handicap hypothesis; Trombiculidae
Document Type: Research article
DOI: 10.1111/j.1365-2435.2007.01251.x
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