Seasonally sympatric but allochronic: differential expression of hypothalamic genes in a songbird during gonadal development

Allochrony, the mismatch of reproductive schedules, is one mechanism that can mediate sympatric speciation and diversification. In songbirds, the transition into breeding condition and gonadal growth is regulated by the hypothalamic-pituitary-gonadal (HPG) axis at multiple levels. We investigated whether the difference in reproductive timing between two, seasonally sympatric subspecies of dark-eyed juncos (Junco hyemalis) was related to gene expression along the HPG axis. During the sympatric pre-breeding stage, we measured hypothalamic and testicular mRNA expression of candidate genes via qPCR in captive male juncos. For hypothalamic mRNA, we found our earlier breeding subspecies had increased expression of gonadotropin-releasing hormone (GnRH) and decreased expression of androgen receptor, estrogen receptor alpha, and mineralocorticoid receptor (MR). Subspecies did not differ in expression of hypothalamic gonadotropin-inhibitory hormone (GnIH) and glucocorticoid receptor (GR). While o...生殖时序错位（Allochrony）指繁殖节律的错配，是可介导同域物种形成与物种分化的机制之一。在鸣禽中，个体进入繁殖状态的过程与性腺发育受下丘脑-垂体-性腺轴（hypothalamic-pituitary-gonadal, HPG）的多层级调控。本研究探讨了两种季节性同域分布的暗眼灯草鹀（Junco hyemalis）亚种间的繁殖时间差异是否与HPG轴相关基因的表达水平相关。在该同域分布种群的繁殖前期，我们通过实时定量PCR（qPCR）检测了圈养雄性暗眼灯草鹀的下丘脑与睾丸组织中候选基因的mRNA表达水平。针对下丘脑mRNA的检测结果显示，繁殖更早的亚种其促性腺激素释放激素（gonadotropin-releasing hormone, GnRH）的表达水平升高，而雄激素受体、雌激素受体α以及盐皮质激素受体（mineralocorticoid receptor, MR）的表达水平降低。两个亚种在下丘脑促性腺激素抑制激素（gonadotropin-inhibitory hormone, GnIH）与糖皮质激素受体（glucocorticoid receptor, GR）的表达水平上并无显著差异。尽管……