Hau M
Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA.
Horm Behav. 2001 Sep;40(2):281-90. doi: 10.1006/hbeh.2001.1673.
Animals need to adjust reproductive decisions to environmental seasonality. In contrast to species from the well-studied temperate zones, little is known for tropical birds about the environmental cues that stimulate reproductive activity and the physiological mechanisms that regulate reproduction. I am investigating the environmental and endocrine mechanisms that underlie the timing of reproduction in spotted antbirds from the near-equatorial Panamanian rainforest and in small ground finches from the equatorial arid Galápagos islands. Spotted antbirds live in a fairly predictable seasonal environment and show regular changes in gonad sizes and some reproductive hormones. Despite the small annual variation in photoperiod close to the equator, these birds can measure slight photoperiodic increases and use it to initiate reproductive activity. Spotted antbirds also respond to seasonal changes in food availability, which allows them to flexibly adjust gonad growth to environmental conditions. Testosterone is involved in regulating song and aggressive behavior in these year-round territorial birds, although it can remain at low plasma levels throughout the year. In contrast, small ground finches exposed to a rather unpredictable climate on Galápagos appear to grow their gonads whenever heavy rains fall and have regressed gonads during other times of the year. The lack of a physiological preparation for the breeding season and their response to short-term cues related to rainfall indicate a striking flexibility in the regulation of breeding in small ground finches. I suggest that tropical birds can serve as model systems to study the physiological adaptations to different environments. Unraveling the neuroendocrine mechanisms behind the flexibility in reproductive timing will clarify whether differences found between temperate and tropical birds represent variations of the same basic mechanism or instead reflect a fundamental divergence in physiological control systems.
动物需要根据环境季节性来调整繁殖决策。与来自研究充分的温带地区的物种不同，对于热带鸟类，关于刺激繁殖活动的环境线索以及调节繁殖的生理机制我们知之甚少。我正在研究近赤道的巴拿马雨林中的斑蚁鸟以及赤道干旱的加拉帕戈斯群岛上的小地雀繁殖时间背后的环境和内分泌机制。斑蚁鸟生活在一个相当可预测的季节性环境中，其性腺大小和一些生殖激素会有规律地变化。尽管赤道附近的光周期年变化很小，但这些鸟类能够察觉到光周期的轻微增加，并利用它来启动繁殖活动。斑蚁鸟还会对食物供应的季节性变化做出反应，这使它们能够根据环境条件灵活调整性腺生长。睾酮参与调节这些全年具有领地意识的鸟类的鸣叫和攻击行为，尽管其血浆水平全年可能保持在较低水平。相比之下，加拉帕戈斯群岛上的小地雀面临着相当不可预测的气候，它们似乎在大雨降临的时候性腺会生长，而在一年中的其他时间性腺会退化。缺乏对繁殖季节的生理准备以及它们对与降雨相关的短期线索的反应表明，小地雀在繁殖调节方面具有显著的灵活性。我认为热带鸟类可以作为研究对不同环境生理适应的模型系统。揭示繁殖时间灵活性背后的神经内分泌机制将阐明，温带和热带鸟类之间发现的差异是代表同一基本机制的变化，还是反映了生理控制系统的根本差异。
