Moore Ignacio T, Perfito Nicole, Wada Haruka, Sperry Todd S, Wingfield John C
Department of Zoology, Box 351800, University of Washington, Seattle, WA 98195, USA.
Gen Comp Endocrinol. 2002 Oct 15;129(1):13-9. doi: 10.1016/s0016-6480(02)00563-4.
Birds breeding in northern latitudes generally have elevated plasma testosterone levels throughout the breeding season with a peak at the onset of the breeding season. In contrast, tropical birds tend to have extremely low plasma testosterone levels year round with only a slight increase during breeding. While these patterns have been consistent in the species investigated, closely related species have not been investigated across a range of latitudes. Birds of the genus Zonotrichia present an ideal opportunity to investigate latitudinal variation in plasma testosterone levels as breeding populations occur from northern Alaska to southern Argentina. We studied three taxa of Zonotrichia: (1) Gambel's white-crowned sparrows, Zonotrichia leucophrys gambelii, breeding at high latitude in northern Alaska, (2) Puget Sound white-crowned sparrows, Z. l. pugetensis, breeding at mid-latitude in Washington state, and (3) an equatorial population of the rufous-collared sparrow, Z. capensis, in Ecuador. To compare both baseline breeding and maximal testosterone levels, males from the three taxa were either bled immediately upon capture during the breeding season or first challenged with gonadotropin-releasing hormone (GnRH) and then bled. As a control, another group of birds experienced a saline challenge. Two-way ANCOVA, with treatment and taxa as factors and testis volume as a covariate, showed a significant effect of treatment on plasma testosterone levels. There was also a significant interaction between taxa and treatment. Contrary to expectations, the equatorial species exhibited greater plasma testosterone levels in response to the GnRH challenge than the high latitude species. There were no differences between the mid- and high-latitude species. The equatorial species had the smallest average testis size and within each taxa there were no relationships between plasma testosterone and testis size. These data suggest that latitudinal clines in plasma testosterone levels in Zonotrichia do not follow previously described patterns and that tropical birds can have levels of testosterone similar to northern latitude species.
在北纬地区繁殖的鸟类通常在整个繁殖季节血浆睾酮水平都会升高，在繁殖季节开始时达到峰值。相比之下，热带鸟类全年血浆睾酮水平往往极低，仅在繁殖期间略有升高。虽然在所研究的物种中这些模式是一致的，但尚未对一系列纬度范围内的近缘物种进行研究。白冠雀属的鸟类提供了一个理想的机会来研究血浆睾酮水平的纬度变化，因为其繁殖种群分布于从阿拉斯加北部到阿根廷南部。我们研究了白冠雀属的三个分类单元：（1）甘贝尔氏白冠雀，Zonotrichia leucophrys gambelii，在阿拉斯加北部高纬度地区繁殖；（2）普吉特海湾白冠雀，Z. l. pugetensis，在华盛顿州中纬度地区繁殖；（3）厄瓜多尔的棕颈白冠雀赤道种群，Z. capensis。为了比较基线繁殖期和最大睾酮水平，来自这三个分类单元的雄性鸟类要么在繁殖季节捕获后立即采血，要么先用促性腺激素释放激素（GnRH）进行刺激然后采血。作为对照，另一组鸟类接受生理盐水刺激。以处理和分类单元为因素、睾丸体积为协变量的双向协方差分析表明，处理对血浆睾酮水平有显著影响。分类单元和处理之间也存在显著的交互作用。与预期相反，赤道物种对GnRH刺激的反应中血浆睾酮水平高于高纬度物种。中纬度和高纬度物种之间没有差异。赤道物种的平均睾丸大小最小，并且在每个分类单元内，血浆睾酮与睾丸大小之间没有关系。这些数据表明，白冠雀属血浆睾酮水平的纬度梯度并不遵循先前描述的模式，并且热带鸟类的睾酮水平可能与北纬地区的物种相似。
