The evolution of female mating preferences: quantifying the benefits

了解产生和维持我们在自然界中看到的惊人表型变异的机制是进化生物学的中心目标之一。一些最引人注目和有趣的特征与吸引配偶有关。孔雀巨大而多彩的线条，雄性天堂鸟奢华的求偶舞蹈，以及柄眼苍蝇的非凡茎——所有这些都是雌性偏好与最精致的雄性交配的结果。然而，令人惊讶的是，科学家们仍然没有完全理解为什么女性应该有这些偏好；选择有更多装饰的雄性对雌性有什么好处？目前的思路将潜在效益分为两类：直接效益和间接效益。直接利益是指雌性直接从雄性那里获得的资源，如食物礼物或对后代的照顾。在这种情况下，男性提供资源的数量或质量与其特征的奢侈程度有关：男性越奢侈，他带来的资源就越好。相反，在间接的好处中，男性特征的奢侈表明了他所携带的基因的质量。因此，雌性与奢侈的雄性交配将产生携带更好基因的后代，因此这些后代将有更大的生存或繁殖机会（他们将具有更高的适应性）。理论模型表明，直接利益可以很容易地解释女性对奢侈男性偏好的进化。然而，在许多系统中似乎没有直接效益，而在这些情况下，则假定会出现间接效益。然而，间接利益的重要性实际上是相当有争议的。例如，预计间接收益很小，因此间接收益不太可能超过女性表达偏好的成本。此外，间接效益可分为优良基因效益和相容基因效益。良好基因的好处来自于雄性拥有的基因，无论与哪只雌性交配，这些基因都能提高后代的适应性。另一方面，相容基因的好处是由于特定的雄性-雌性组合产生具有高遗传适应性价值的后代（即特定的雄性和雌性具有彼此相容的基因）。如果雌性选择雄性是基于相容的基因利益，那么不同的雌性就不会选择相同的雄性，因此雌性的交配偏好不会导致奢侈的雄性特征的进化。雌性是否根据良好或相容的基因利益来选择取决于两件事：这些利益的相对大小和使雌性能够根据这些利益在雄性之间做出选择的信号的存在。然而，对这两件事的估计很少。此外，对雌性配偶选择的直接和间接好处都可能发生在同一物种中，但目前它们通常是单独研究的，因此我们对它们之间的相对重要性知之甚少。我建议提供这些关键缺失参数的估计，从而为在女性交配偏好的进化中发挥作用的直接和间接利益的潜力提供新的见解。在这个过程中，这项研究将产生的数据将提高我们对表型性状的遗传基础的理解，这是进化生物学的一个基本目标，它影响我们对基因型如何转化为表型的理解，以及我们对表型如何响应选择而变化的预测。

Understanding the mechanisms that generate and maintain the spectacular phenotypic variation we see in nature is one of the central aims of evolutionary biology. Some of the most eye-catching and intriguing traits are associated with attracting a mate. The enormous and colourful train of the peacock, the extravagant courtship dance of male birds of paradise and the extraordinary stalks of stalk eyed flies- all are a result of female preferences for mating with the most elaborate male. Yet, surprisingly, scientists still do not have a complete understanding of why females should have these preferences; what benefits do females gain from choosing more ornamented males? Current thinking divides the potential benefits into two categories: direct benefits and indirect benefits. Direct benefits are resources females gain directly from the male such as gifts of food, or care for the offspring. In these, the amount or quality of resources a male provides is related to the extravagance of his trait: the more extravagant the male, the better the resource he brings. In contrast, with indirect benefits, the extravagance of a male's trait indicates the quality of the genes he is carrying. Females mating with an extravagant male will therefore produce offspring carrying better genes, and so these offspring will have a greater chance of surviving or reproducing (they will have higher fitness). Theoretical models show that direct benefits can easily explain the evolution of female preferences for extravagant males where they exist. However, direct benefits seem to be absent in many systems, and in these cases indirect benefits are assumed to occur instead. However, the importance of indirect benefits is actually rather controversial. For example, indirect benefits are predicted to be small, making it unlikely that indirect benefits will outweigh the costs to females of expressing a preference. In addition, indirect benefits can be split into good genes benefits and compatible genes benefits. Good genes benefits result from genes a male possesses that will improve the fitness of his offspring regardless of which female he mates with. Compatible genes benefits, on the other hand, result from a particular male-female combination producing offspring with high genetic value for fitness (i.e. particular males and females have genes which are compatible with one another). If females choose males based on compatible genes benefits, different females are not expected to prefer the same males and so female mating preferences will not lead to the evolution of extravagant male traits. Whether females choose based on good or compatible genes benefits depends on two things: the relative magnitude of these benefits and the existence of signals enabling females to choose between males based on these benefits. However, estimates of these two things are rare. In addition, direct and indirect benefits to female mate choice both might occur in the same species, but at the moment they are typically examined in isolation, and so we have little idea of how important they are relative to one another. I propose to provide estimates of these key missing parameters and therefore provide new insights into the potential for direct and indirect benefits to play a role in the evolution of female mating preferences. In the process, this research will generate data that will improve our understanding of the genetic basis to phenotypic traits, a fundamental aim of evolutionary biology that affects our understanding of how genotypes translate to phenotypes and our predictions of how phenotypes will change in response to selection.