Publisher Information: Uppsala universitet, Institutionen för medicinsk biokemi och mikrobiologi Washington State Univ, Sch Biol Sci, Pullman, WA 99164 USA.;Cornell Univ, Dept Neurobiol & Behav, Ithaca, NY 14853 USA.;Cornell Lab Ornithol, Ithaca, NY USA. Tulane Univ, Dept Ecol & Evolutionary Biol, New Orleans, LA 70118 USA. Tulane Univ, Dept Ecol & Evolutionary Biol, New Orleans, LA 70118 USA. Cornell Univ, Dept Neurobiol & Behav, Ithaca, NY 14853 USA.;Cornell Lab Ornithol, Ithaca, NY USA. Tulane Univ, Dept Ecol & Evolutionary Biol, New Orleans, LA 70118 USA. Tulane Univ, Dept Ecol & Evolutionary Biol, New Orleans, LA 70118 USA. Tulane Univ, Dept Ecol & Evolutionary Biol, New Orleans, LA 70118 USA. Washington State Univ, Sch Biol Sci, Pullman, WA 99164 USA. Elsevier BV 2022
نبذة مختصرة : Androgens like testosterone mediate suites of physical and behavioral traits across vertebrates, and circulation varies considerably across and within taxa. However, an understanding of the causal factors of variation in circulating testosterone has proven difficult despite decades of research. According to the challenge hypothesis, agonistic interactions between males immediately prior to the breeding season produce the highest levels of testosterone measured during this period. While many studies have provided support for this hypothesis, most species do not respond to male-male competition by elevating testosterone. As a result, a recent revision of the hypothesis ('challenge hypothesis 2.0') places male-female interactions as the primary cause of rapid elevations in testosterone circulation in male vertebrates. Here, we offer a test of both iterations of the challenge hypothesis in a tropical bird species. We first illustrate that male White-shouldered Fairywrens (Malurus alboscapulatus) differ by subspecies in plasma androgen concentrations. Then we use a social network approach to find that males of the subspecies with higher androgens are characterized by greater social interaction scores, including more time aggregating to perform sexual displays. Next, we use a controlled experiment to test whether males respond to simulated territorial intrusion and/or courtship competition contexts by elevating androgens. We found that males elevated androgens during territorial intrusions relative to flushed controls, however, males sampled during courtship competitions had greater plasma androgens both relative to controls and males sampled while defending territories. Ultimately, our results are consistent with challenge hypothesis 2.0, as sexual interactions with extra-pair females were associated with greater elevation of androgens than territorial disputes.
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