title: Experimental elevation of testosterone lowers fitness in female dark-eyed juncos.
abstract: Testosterone (T) is often referred to as the "male hormone," but it can influence aggression, parental behavior, and immune function in both males and females. By experimentally relating hormone-induced changes in phenotype to fitness, it is possible to ask whether existing phenotypes perform better or worse than alternative phenotypes, and hence to predict how selection might act on a novel or rare phenotype. In a songbird, the dark-eyed junco (Junco hyemalis), we have examined the effects of experimentally elevated T in females on fitness-related behaviors such as parental care. In this study, we implanted female juncos with exogenous T and examined its effect on fitness (survival, reproduction, and extra-pair mating) to assess whether T-altered phenotypes would prove to be adaptive or deleterious for females. Experimental elevation of T decreased the likelihood that a female would breed successfully, and T-implanted females had lower total reproductive success at every stage of the reproductive cycle. They did not, however, differ from control females in fledgling quality, extra-pair offspring production, survival, or reproduction in the following year. Previous work in this system has shown that experimental elevation of T in males alters behavior and physiology and decreases survival but increases the production of extra-pair offspring, leading to higher net fitness relative to control animals. Our results suggest that increased T has divergent effects on male and female fitness in this species, and that prevailing levels in females may be adaptive for them. These findings are consistent with sexual conflict.
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA. nmgerlac@indiana.edu
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Gerlach
authors.forename: Ellen D
authors.initials: ED
authors.lastname: Ketterson
mesh_terms: D000818:Animals; D005260:Female; D008297:Male; D009425:Nesting Behavior / Q000187:drug effects* / Q000502:physiology; D012098:Reproduction / Q000187:drug effects* / Q000502:physiology; D012726:Sexual Behavior, Animal / Q000187:drug effects* / Q000502:physiology; D046370:Sparrows / Q000502:physiology*; D013739:Testosterone / Q000097:blood / Q000494:pharmacology*
chemical_list: D013739:Testosterone