Hormone-related Differences and Similarities in Song Birds

男性和女性通常在某些方面相似，而在其他方面不同。差异的产生可能是因为一种性别比另一种性别面临更大的生殖竞争（性选择），或者因为两性在生态上的差异（自然选择）。由于男性和女性拥有相同的基因组，他们也会受到相关选择的影响，当一种性别直接选择的基因变异（“如父如子”）被另一种性别携带（“如父如女”）时，就会发生这种情况。如果直接有利于一种性别的属性也有利于另一种性别，那么相关选择可以加速进化，或者当这些属性对第二性别不利时，相关选择可能成为一种约束。性别差异和相似性的潜在机制包括发育程序、类固醇激素和导致性别分化组织的基因表达中与类固醇无关的差异。性腺类固醇可以在发育早期组织组织，使它们在以后的生活中对类固醇的激活有或有（或没有）反应。性腺激素也会影响成年后的性别，当它们的作用相似时，就有可能存在相关选择。这一提议的重点是类固醇激素，睾酮，以及它对鸣禽物种黑眼junco的成年雄性和雌性的性别差异和相似性的综合影响。该研究有四个目标：(1)通过比较雄性和雌性激素水平的自然特征，雌性对已知增加雄性T的刺激的激素反应，以及通过对外受精（EPFs）产生和不产生后代的雌性激素水平，来评估睾丸激素在性整合中的作用。两性之间的相似性将揭示相关选择的可能性。(2)通过实验改变循环睾酮水平，并将改变后的女性睾酮对男性的影响与之前的结果进行比较。个体实验将探讨雌性睾酮水平升高是否会改变对雄性的吸引力（性选择），以及它是否会影响亲代行为、社会地位或免疫功能（自然选择）。他们还将讨论睾酮、皮质酮、皮质类固醇结合球蛋白之间的相互作用。(3)确定女性对睾酮改变的反应是有益的、中性的还是有害的。如果两性之间相互制约，那么对一个性别有益的改变可能对另一个性别有害。如果两性相互加强，那么改变可能对两性都有益。如果性别是独立的，那么已知的对男性有益或有害的改变可能对女性的适应性没有影响。(4)比较亲缘度对性选择性状和两种激素相关性状的影响。研究人员将对具有已知遗传亲缘关系的幼鸟在体型和影响吸引力的羽毛特征方面的家族相似性进行评估。将饲养更多的juncos，并对三种激素介导的性状进行比较。遗传相关性的存在可以预测相关选择；缺少一个就预示着性独立。本提案中描述的研究将为培养不同背景的未来科学家提供机会，使他们能够进行实验室和实地实验，解决生物差异的近似和最终解释的整合问题。它还将丰富印第安纳大学的研究生和本科生课程。这些发现的潜在社会意义包括：(1)环境中激素活性物质的重要性；(2)为保护而改进圈养鸣禽的繁殖方法；(3)加深对性和性别之间关系的理解。

LAY SUMMARYMales and females typically resemble one another in some ways and differ in others. Differences may arise because one sex is subject to greater reproductive competition than the other (sexual selection) or because the sexes differ in their ecology (natural selection). Because males and females share a common genome, they are also subject to correlated selection, which occurs when genetic variants directly favored by selection in one sex ('like father, like son') are carried along in the other sex ('like father, like daughter'). Correlated selection can hasten evolution if attributes directly favored in one sex also benefit the other, or it may serve as a constraint when the attributes are disadvantageous to the second sex.Proximate mechanisms underlying sex differences and resemblances include developmental programs, steroid hormones, and steroid-independent differences in gene expression that lead to sexually differentiated tissues. Gonadal steroids can act early in development to organize tissues so that they are or are (or are not) responsive to activation by a steroid later in life. Gonadal steroids can also affect the sexes as adults, and, when their effects are similar, there is potential for correlated selection. The focus of this proposal is the steroid hormone, testosterone, and its integrating effect on sex differences and resemblances in adult males and females of a songbird species, the dark-eyed junco. The research has four objectives: (1) to assess the role of testosterone in sexual integration by comparing natural profiles of male and female hormone levels, hormonal response of females to stimuli known to increase T in males, and hormone levels in females that do and do not produce young by extra-pair fertilizations (EPFs). Resemblance between the sexes will reveal the potential for correlated selection.(2) to alter the level of circulating testosterone experimentally and compare effects of altered testosterone in females to previous results from males. Individual experiments will address whether elevated testosterone in females alters attractiveness to males (sexual selection) and whether it affects parental behavior, social status, or immune function (natural selection). They will also address interactions between testosterone, corticosterone, corticosteroid binding globulins.(3) to determine whether female responses to altered testosterone are beneficial, neutral, or detrimental in the field. If the sexes constrain one another, alterations that are beneficial in one sex should be detrimental in the other. If the sexes reinforce one another, alterations may be beneficial in both sexes. If the sexes are independent, then alterations already known to be beneficial or detrimental in males may have no fitness consequences for females. (4) to compare how degree of relatedness affects a sexually selected trait and two hormone-related traits. Juncos of known genetic relatedness will be assessed for family resemblance in measures of body size and a plumage trait that affects attractiveness. Additional juncos will be reared and compared for three hormonally mediated traits. The presence of a genetic correlation would predict correlated selection; the absence of one would predict sexual independence.Research described in this proposal will provide opportunities for training future scientists of diverse backgrounds in the conduct of laboratory and field experiments that address the integration of proximate and ultimate explanations for biological differences. It will also enrich graduate and undergraduate courses taught at Indiana University. Potential societal implications of the findings to be expected include (1) importance of hormonally active agents in the environment, (2) improved methods for breeding captive songbirds for conservation, and (3) a greater understanding of the relationship between sex and gender.