Genetic basis of female sexual preference in a stalk-eyed fly

公众和科学家对理解夸张的男性性装饰是如何通过女性配偶偏好进化的有相当大的兴趣。最近对性选择的兴趣已经转向理解男性装饰物变化的原因，包括遗传和环境，以及这些特征的信号价值。相反，人们忽视了对女性性偏好变化的深入研究。这在一定程度上反映了准确量化偏好的难度--这需要反复测量女性对各种男性刺激的反应，而这往往很难在实验室条件下进行研究。这也反映出人们对女性偏好行为的可变性和复杂性普遍认识不足。我们已经开发了一个很好的系统，用于量化非洲茎眼蝇Diasemopsis meigenii的雌性择偶偏好的变化。在这个物种中，女性积极拒绝不想要的男性交配尝试。这使我们能够制定协议，以准确地衡量个别女性的择偶偏好。我们以前已经证明，偏好的强度变化与女性的eyespan和女性生殖力的表型变异呈正相关。需要解决的一个关键问题是女性择偶偏好变异的遗传基础。没有遗传变异，雌性偏好就无法进化。我们将开展首个偏好遗传的QTL（quantitative trait locus）研究。这将揭示偏好变异背后的可分离遗传因素的数量。可能有一个或两个遗传因素具有主要影响，或者基因在整个基因组中的效应大小分布更均匀。它还将揭示偏好基因的连锁模式，以及是否像某些理论预测的那样，存在对X染色体的偏好。我们要研究的另一个关键问题是偏好依赖于条件的证据。最近的几项研究表明，在优质资源免费提供的良好条件下饲养的雌性比在劣质资源上饲养的雌性有不同的偏好。例如，在我们以前的工作中，我们已经表明，女性柄眼苍蝇获得更好的幼虫或成人资源有更强的方向偏好男性较大的性装饰。这对性选择的强度有着广泛的影响，如果条件最好的雌性不仅对与谁交配表现出最大的辨别力，而且也是最多产的。我们将使用定量遗传学研究探讨条件依赖性偏好的遗传学。基因相关的家庭将在三种食物质量不同的环境中长大。环境变化可能会压倒遗传信号。但从我们之前测量男性特征对环境压力的反应的研究来看，我们并不期望这样。相反，我们认为恶劣的环境会放大雌性之间的遗传差异，带来偏好的遗传变异。因此，一些雌性基因型在所有环境中都能持续产生强烈的偏好，而另一些基因型则会随着环境条件的恶化而表现出下降的偏好。我们将在QTL研究中进一步探讨这一预测。我们已经表明，在柄眼蝇的女性偏好的强度与女性eyespan和女性生育力，两个特征，强烈反映了在幼虫和成人的发展，分别可用的资源。我们将检验雌性偏好QTL是否与雌性眼距QTL和雌性生殖力QTL位于相同的基因组区域。这种模式可能表明，相同的基因条件下的几个特征，如偏好，眼睛跨度和繁殖力。

There is considerable interest amongst the general public and scientists in understanding how exaggerated male sexual ornaments have evolved through female mate preferences. Much recent interest in sexual selection has been directed toward understanding the causes of variation in male ornaments, both genetic and environmental, and the signalling value of these traits. In contrast, there has been a neglect of in depth studies of variation in female sexual preferences. This in part reflects the difficulty of accurately quantifying preferences - which requires repeated measures of female responses to a variety of male stimuli, which are often difficult to study under laboratory conditions. It also reflects a general under appreciation of the variability and complexity of female preference behaviour. We have already developed an excellent system for quantifying variation in female mate preference in the African stalk-eyed fly Diasemopsis meigenii. In this species, females actively reject unwanted male mating attempts. This has allowed us to develop protocols to accurately measure individual female mate preferences. We have previously demonstrated that the strength of preference varies positively with phenotypic variation in female eyespan and female fecundity. A key question to address is the genetic underpinnings of variation in female mate preferences. Without genetic variation female preference cannot evolve. We will carry out the first QTL (quantitative trait locus) study of the genetics of preference. This will uncover the number of separable genetic factors underlying variation in preference. It may be that there are one or two genetic factors with major effects or alternatively a more even distribution of effect sizes of genes across the genome. It will also reveal the linkage pattern of preference genes and whether there is a bias towards the X-chromosome, as some theory predicts. Another critical issue that we will investigate is the evidence that preferences are condition-dependent. Several recent studies have shown that females reared under good conditions in which high quality resources are freely available have different preferences than females reared on poor quality resources. For example, in our previous work, we have shown that female stalk-eyed flies with access to better larval or adult resources have stronger directional preferences for males with larger sexual ornaments. This has wide ranging implications for the strength of sexual selection, if the females with the highest condition not only show the greatest discrimination of who they mate with but are also the most fecund. We will investigate the genetics of condition-dependent preferences using a quantitative genetic study. Genetically related families will be raised in three environments which vary in food quality. It is possible that the environmental variation will overwhelm the genetic signal. But from our previous studies measuring the responses of male traits to environmental stress, we do not expect this. Rather we believe that the harsh environment will amplify genetic differences between females, bringing out genetic variation in preference. So some female genotypes will consistently produce strong preference in all environments, whereas others genotypes will show declining preference as environmental conditions deteriorate. We will further probe this prediction in our QTL study. We have already shown that the strength of female preference in stalk-eyed flies covaries with female eyespan and female fertility, two traits that strongly reflect resources available during larval and adult development respectively. We will test whether QTL for female preference are located in the same genomic regions as QTL for female eyespan and QTL for female fecundity. This pattern could indicate that the same genes for condition underlie several traits such as preference, eyespan and fecundity.