Maney Donna L, Horton Brent M, Zinzow-Kramer Wendy M
Department of Psychology, Emory University, Atlanta, GA 30322, USA
Department of Psychology, Emory University, Atlanta, GA 30322, USA.
Integr Comp Biol. 2015 Aug;55(2):323-31. doi: 10.1093/icb/icv005. Epub 2015 Apr 7.
Trade-offs between competitive and parental strategies often are mediated by sex steroids. The mechanisms underlying steroid signaling and metabolism may therefore serve as targets of disruptive selection that leads to alternative behavioral phenotypes. White-throated sparrows exhibit two color morphs that differ in both competitive and parental behavior; white-striped (WS) birds engage in more territorial singing, whereas tan-striped (TS) birds provision nestlings more often. Although WS birds have higher levels of plasma testosterone (T) and estradiol than do TS birds, experimental equalization of these hormones does not abolish morph differences in singing. Neural sensitivity to sex steroids may differ between the morphs because the gene for estrogen receptor alpha (ERα) has been captured by a chromosomal rearrangement found only in the WS birds. We recently showed that expression of this gene differs between the morphs and may drive the behavioral polymorphism. First, the ERα promoter region contains fixed polymorphisms that affect transcription efficiency in vitro. Second, in a free-living population, local expression of ERα depends strongly on morph and predicts both territorial singing and parental provisioning. Differential ERα expression is particularly striking in the medial amygdala; WS birds have three times more ERα mRNA than do TS birds. This difference persists during the non-breeding season and is unaffected by exogenous T treatment. Finally, preliminary data generated by RNA-seq confirm that ERα expression in MeA is both differentially expressed and correlated with territorial singing. Together, these results suggest that ERα may be a target of disruptive selection that leads to alternative behavioral strategies. Our future directions include a more detailed analysis of the ERα promoter regions to determine the molecular basis of differential expression as well as gene network analyses to identify genes connected to ERα.
竞争策略和育雏策略之间的权衡通常由性类固醇介导。因此，类固醇信号传导和代谢的潜在机制可能成为导致行为表型差异的间断性选择的目标。白喉带鹀表现出两种颜色形态，在竞争行为和育雏行为上都有所不同；白色条纹（WS）的鸟更频繁地进行领地鸣叫，而褐色条纹（TS）的鸟则更频繁地哺育雏鸟。尽管WS鸟的血浆睾酮（T）和雌二醇水平高于TS鸟，但对这些激素进行实验性均衡并不能消除鸣叫形态上的差异。不同形态的鸟对性类固醇的神经敏感性可能不同，因为雌激素受体α（ERα）基因已被仅在WS鸟中发现的染色体重排捕获。我们最近表明，该基因在不同形态之间的表达存在差异，可能驱动了行为多态性。首先，ERα启动子区域包含固定的多态性，这些多态性在体外会影响转录效率。其次，在一个自由生活的种群中，ERα的局部表达强烈依赖于形态，并能预测领地鸣叫和育雏行为。ERα的差异表达在内侧杏仁核中尤为显著；WS鸟的ERα mRNA比TS鸟多两倍。这种差异在非繁殖季节持续存在，并且不受外源性T处理的影响。最后，RNA测序产生的初步数据证实，内侧杏仁核中ERα的表达不仅存在差异表达，而且与领地鸣叫相关。总之，这些结果表明ERα可能是导致行为策略差异的间断性选择的目标。我们未来的方向包括对ERα启动子区域进行更详细的分析，以确定差异表达的分子基础，以及进行基因网络分析，以识别与ERα相关的基因。
