Steiger Silke S, Goymann Wolfgang, Kempenaers Bart
Department Behavioural Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, Postfach 1564, 82305 Starnberg, Seewiesen, Germany.
Gen Comp Endocrinol. 2006 Jun;147(2):133-40. doi: 10.1016/j.ygcen.2005.12.015. Epub 2006 Feb 7.
Steroid hormones are predicted to vary with mating systems, degree of paternal care and aggression, as proposed in the "challenge hypothesis." We measured plasma concentrations of testosterone (T) and 5alpha-dihydrotestosterone (DHT) in two high Arctic breeding and closely related shorebird species, the polygynous pectoral sandpiper (Calidris melanotos) and the monogamous semipalmated sandpiper (Calidris pusilla) to examine whether the hormonal findings corroborate the predictions of the challenge hypothesis. In both species, males showed significantly higher levels of DHT and T than females, but in pectoral sandpipers median T levels were 34 times greater in males than in females, whereas in semipalmated sandpiper there was only a 4.9-fold difference. T and DHT concentrations correlated in semipalmated sandpipers and in male, but not in female, pectoral sandpipers. In semipalmated sandpipers, androgen levels were highest in the beginning of the breeding season and then declined, whereas male pectoral sandpipers showed extremely high androgen levels which were sustained throughout the breeding season. In both species, androgen levels were independent of body condition. Several incubating male semipalmated sandpipers had high circulating T levels, suggesting that low T is not required to exhibit paternal care. Our results are consistent with the challenge hypothesis in that androgen concentrations were higher throughout the breeding season in the polygynous compared to the monogamous species. Our study also supports previous studies suggesting that the short breeding season in the high Arctic and the importance of male care to nest success may be factors leading to behavioral T insensitivity.
正如“挑战假说”所提出的，类固醇激素预计会随着交配系统、父性照料程度和攻击性而变化。我们测量了两种北极高纬度繁殖且亲缘关系密切的滨鸟——多配性的胸斑滨鹬（Calidris melanotos）和单配性的半蹼滨鹬（Calidris pusilla）血浆中的睾酮（T）和5α-双氢睾酮（DHT）浓度，以检验激素研究结果是否证实了挑战假说的预测。在这两个物种中，雄性的DHT和T水平均显著高于雌性，但在胸斑滨鹬中，雄性的T中位数水平是雌性的34倍，而在半蹼滨鹬中，两者仅相差4.9倍。半蹼滨鹬以及雄性胸斑滨鹬（而非雌性胸斑滨鹬）的T和DHT浓度存在相关性。在半蹼滨鹬中，雄激素水平在繁殖季节开始时最高，随后下降，而雄性胸斑滨鹬的雄激素水平极高且在整个繁殖季节持续保持。在这两个物种中，雄激素水平均与身体状况无关。几只正在孵卵的雄性半蹼滨鹬具有较高的循环T水平，这表明表现出父性照料并不需要低T水平。我们的结果与挑战假说一致，即与单配性物种相比，多配性物种在整个繁殖季节的雄激素浓度更高。我们的研究还支持了先前的研究，这些研究表明北极高纬度地区较短的繁殖季节以及雄性照料对巢穴成功的重要性可能是导致行为上对T不敏感的因素。
