Wingfield J C, Vleck C M, Moore M C
Department of Zoology, University of Washington, Seattle 98195.
J Exp Zool. 1992 Dec 15;264(4):419-28. doi: 10.1002/jez.1402640407.
Many avian species of the North American Sonoran desert, e.g., the black-throated sparrow, Amphispiza bilineata, cactus wren, Campylorhynchus brunneicapillus, and curve-billed thrasher, Toxostoma curvirostre, can potentially breed from March/April to August. It is possible that, at least in summer, intense heat and aridity may have inhibitory effects on breeding by precipitating a stress response. Stress typically results in a rise in secretion of adrenocorticosteroid hormones that then inhibit reproduction by suppressing release of gonadal hormones. However, we found that plasma levels of corticosterone were not higher during summer, compared with winter, even in 1989 when summer temperatures were higher than normal. In June 1990, temperatures were also above normal and soared to the highest level recorded in Arizona (50 degrees C). Plasma levels of corticosterone during June were high in black-throated sparrows, but less so in two other species (Abert's towhee, Pipilo aberti, and Inca dove, Scardafella inca) found in more shady riparian and suburban habitat with constant access to water. The adrenocortical response to stress (as measured by the rate of corticosterone increase following capture) was reduced in the hottest summer months in black-throated sparrows, cactus wrens, and curve-billed thrashers, but less so in Abert's towhee an Inca dove. These data suggest that at least some birds breeding in the open desert with restricted access to water are able to suppress the classical adrenocortical response to stress. The response is then reactivated in winter after breeding has ceased. It is possible that this stress modulation may allow breeding to continue despite severe heat. Analysis of plasma from these species indicated that the apparent modulation of the adrenocortical response to stress was not an artifact of reduced affinity or capacity of corticosterone binding proteins.
北美索诺兰沙漠的许多鸟类，如黑喉雀（Amphispiza bilineata）、仙人掌鹪鹩（Campylorhynchus brunneicapillus）和弯嘴嘲鸫（Toxostoma curvirostre），都有可能在3月/4月至8月繁殖。至少在夏季，酷热和干旱可能通过引发应激反应对繁殖产生抑制作用。应激通常会导致肾上腺皮质类固醇激素分泌增加，进而通过抑制性腺激素的释放来抑制繁殖。然而，我们发现，即使在1989年夏季气温高于正常水平时，与冬季相比，夏季血浆皮质酮水平也没有更高。1990年6月，气温同样高于正常水平，并飙升至亚利桑那州记录的最高水平（50摄氏度）。6月，黑喉雀的血浆皮质酮水平较高，但在其他两种鸟类（艾氏灯草雀，Pipilo aberti，和印加鸽，Scardafella inca）中较低，这两种鸟生活在有更多阴凉的河岸和郊区栖息地，且能持续获取水源。在最炎热的夏季月份，黑喉雀、仙人掌鹪鹩和弯嘴嘲鸫对应激的肾上腺皮质反应（通过捕获后皮质酮增加率来衡量）有所降低，但艾氏灯草雀和印加鸽的降低程度较小。这些数据表明，至少一些在开阔沙漠中繁殖且获取水源受限的鸟类能够抑制对应激的经典肾上腺皮质反应。这种反应在繁殖停止后的冬季会重新激活。尽管酷热难耐，但这种应激调节可能使繁殖得以继续。对这些物种血浆的分析表明，肾上腺皮质对应激反应的明显调节并非皮质酮结合蛋白亲和力或能力降低的假象。
