Department of Biology, University of Washington, Seattle, WA 98195, USA.
Horm Behav. 2011 Jul;60(2):195-201. doi: 10.1016/j.yhbeh.2011.05.002. Epub 2011 May 14.
Most work investigating modulation of testosterone (T) levels in birds has focused on northern temperate and Arctic species, and to a lesser degree, tropical species. Studies exploring modulation of T in birds in temperate regions of the Southern Hemisphere are lacking. Here we explore patterns of T secretion across the breeding season in two populations of temperate Zonotrichia capensis in Chile, located only 130 km apart, but separated by 2000 m in elevation. We then compared these T profiles to those of conspecifcs in the tropics and congeners in northern zones. We measured baseline T levels during pre-breeding in lowland Z. c. chilensis, early breeding in highland Z. c. chilensis and mid-breeding in both populations. We also tested for social stimulation of T secretion during mid-breeding in both populations. Lastly, we challenged the hypothalamic-pituitary-gonadal (HPG) axis of the lowland population with gonadotropin-releasing hormone (GnRH) to determine maximum possible T production. We found that the highland population adjusted T secretion across the breeding season like northern species. Neither Z. c. chilensis population modulated T in response to social stimuli, nor the HPG axis of the lowland population was not maximally active during either pre- or mid-breeding. These results suggest that patterns of circulating T in the highland population of Z. c. chilensis in the Southern Hemisphere are similar to congeners in the temperate Northern Hemisphere, but those of the lowland population of Z. c. chilensis are not, and are more similar to conspecifics breeding in the tropics.
大多数研究鸟类睾丸酮（T）水平调节的工作都集中在北温带和北极物种上，在较小程度上也集中在热带物种上。探索南半球温带地区鸟类 T 调节的研究较少。在这里，我们研究了位于智利相距仅 130 公里但海拔相差 2000 米的两个温带 Zonotrichia capensis 种群在繁殖季节的 T 分泌模式。然后，我们将这些 T 谱与热带地区的同属种和北方地区的同属种进行了比较。我们在低地 Z. c. chilensis 的繁殖前期间测量了基线 T 水平，在高地 Z. c. chilensis 的早期繁殖期间测量了基线 T 水平，并在两个种群的繁殖中期测量了基线 T 水平。我们还测试了两个种群繁殖中期 T 分泌的社会刺激作用。最后，我们用促性腺激素释放激素（GnRH）对低地种群的下丘脑-垂体-性腺（HPG）轴进行了挑战，以确定最大可能的 T 产生量。我们发现，高地种群在繁殖季节调整 T 分泌的方式与北方物种相似。Z. c. chilensis 两个种群均未根据社会刺激来调节 T，也未在繁殖前或繁殖中期使低地种群的 HPG 轴达到最大活性。这些结果表明，南半球高海拔 Z. c. chilensis 种群循环 T 的模式与北半球温带地区的同属种相似，但低地 Z. c. chilensis 种群的模式则不然，与热带地区繁殖的同属种更为相似。
