Dissertation Research: The Evolutionary Genetics of Sexual Dimorphism

自然界最大的谜团之一是关于为什么同一物种的雄性和雌性在许多形态特征上经常不同。性大小二形性(SSD)，即两性之间平均身体大小的差异，特别令人感兴趣，因为身体大小对个人的健康状况起着核心作用。随着新的统计工具的出现和概念的进步，对SSD演变的研究已经从传统的时间静态、单一压力、单一性别的视角转移到更强有力的观点，即跨越多代人的多种选择性力量在两性之间相互作用。然而，为了充分解释这些选择压力的进化含义，我们还必须知道男性和女性体型的潜在遗传结构。这是正确的，因为遗传结构可能会改变或限制对选择的二态反应。不幸的是，很少有研究将他们对SSD的研究扩展到所涉及的选择压力的范围之外，这造成了关于二型性进化遗传学的信息匮乏。这项提案中提出的目标将调查已知从多个来源中选择的性二型性状的潜在遗传结构。本研究将采用经验性数量遗传方法为两性产生体型和其他两个重要相关性状的方差协方差矩阵(G-矩阵)。这将允许性别之间比较遗传结构的差异，并测试性别之间可能限制二态进化的同源特征的显著相关性。此外，当G矩阵与描述选择方向和强度的选择梯度相结合时，可以预测遗传协方差是否会对特征进化产生显著影响，这种影响是否会限制或加强特征进化，以及二态是否仍在进化。这项研究的结果将是普遍感兴趣的，因为它们可能会对许多其他系统中许多其他特征的性别差异产生影响。

One of the great mysteries of the natural world concerns why males and females of the same species often differ in many morphological characters. Sexual size dimorphism (SSD), or the difference in mean body size between the sexes, is of particular interest since body size plays a central role in the fitness of an individual. With the advent of new statistical tools and conceptual advances, investigations into the evolution of SSD have moved from the traditional temporally static, single pressure, single sex perspective, to the more robust view of multiple selective forces interacting in both sexes across many generations. However, to fully interpret the evolutionary implications of these selective pressures, one must also know the underlying genetic architecture of male and female body size. This is true since genetic architecture may alter or constrain a dimorphic response to selection. Unfortunately, few studies have expanded their investigation of SSD beyond the scope of the selective pressures involved, creating a dearth of information regarding the evolutionary genetics of dimorphism. The objectives set forth in this proposal will investigate the underlying genetic structure of a sexually dimorphic trait that is known to be under selection from multiple sources. This study will employ an empirical quantitative genetic approach to generate for both sexes the variance covariance matrices (G-matrices) for body size and two other important correlated traits under selection. This will permit comparison between the sexes for differences in genetic architecture and tests for significant correlations between the sexes for homologous traits that may constrain dimorphic evolution. In addition, when G-matrices are coupled with selection gradients that describe the direction and intensity of selection, one can predict if genetic covariances will have a significant effect on trait evolution, if this effect constrains or reinforces trait evolution, and if dimorphism is still evolving. The results of this study will be of general interest as they will likely have bearing on gender-based differences for many other traits in many other systems.