Department of Biology, Texas A&M University, 3258 TAMU College Station, TX 77843, USA.
Integr Comp Biol. 2020 Sep 1;60(3):703-711. doi: 10.1093/icb/icaa095.
Seasonal reproduction is a widespread adaptation in vertebrates, such that individuals time their reproductive efforts to match peak resource abundance. Individuals rely on environmental cues to regulate hormonal mechanisms governing timing of breeding. Historically, studies on physiological mechanisms of seasonal reproduction, specifically in birds, have disproportionately focused on males compared to females. For this review, I conducted a literature search of the last decade of avian research and found a persistent sex bias in the field of physiological mechanisms of seasonal reproduction. Using work conducted with the dark-eyed junco (Junco hyemalis) as a case study, I present a possible solution to combat the sex bias: natural comparisons of populations that differ in reproductive timing to investigate mechanisms of reproduction in both sexes. Populations of dark-eyed juncos that differ in migratory behavior (i.e., migrant and resident) exhibit overlapping ranges during winter and early spring; residents begin breeding in early spring prior to the departure of migrants. This system, and others like it, provides an opportunity to compare mechanisms of reproduction in populations that differ in reproductive timing despite experiencing the same environmental conditions in early spring. In juncos, migrant and resident females and males exhibit similar patterns of hypothalamic regulation of reproduction in early spring, but sex differences in gonadal sensitivity between the populations could be an important distinction that partially explains sex differences in reproductive development. Comparing mechanisms of reproduction in free-living populations and in captivity can reveal important mechanisms that determine the onset of reproductive development, as well as potential sex differences in these mechanisms. Understanding the mechanisms of reproductive phenology has important implications for understanding how species will survive and reproduce in a changing climate.
季节性繁殖是脊椎动物中广泛存在的一种适应现象，即个体将繁殖努力的时间与资源最丰富的高峰期相匹配。个体依赖环境线索来调节控制繁殖时间的激素机制。从历史上看，关于季节性繁殖的生理机制的研究，特别是在鸟类中，与雌性相比，对雄性的关注不成比例。在本次综述中，我对过去十年的鸟类研究进行了文献检索，发现季节性繁殖的生理机制领域存在持续的性别偏见。我使用暗眼灯草雀（Junco hyemalis）的研究工作作为案例研究，提出了一种可能的解决方案来解决性别偏见问题：对繁殖时间不同的种群进行自然比较，以研究两性的繁殖机制。在暗眼灯草雀中，具有不同迁徙行为（即迁徙和留居）的种群在冬季和早春期间的活动范围重叠；留居种群在早春开始繁殖，而迁徙种群在留居种群离开之前开始繁殖。这个系统和其他类似的系统为比较繁殖时间不同的种群的繁殖机制提供了机会，尽管它们在早春经历了相同的环境条件。在暗眼灯草雀中，迁徙和留居的雌性和雄性在早春时表现出相似的下丘脑调节繁殖的模式，但种群之间的性腺敏感性的性别差异可能是一个重要的区别，部分解释了繁殖发育中的性别差异。比较自由生活种群和圈养种群的繁殖机制可以揭示决定繁殖发育开始的重要机制，以及这些机制中可能存在的性别差异。了解繁殖物候学的机制对于了解物种在气候变化下如何生存和繁殖具有重要意义。
