Poor starts and silver spoons: how diet shapes sex-specific fitness from birth to death

“. .我想我不会长得这么快，因为甜蜜的花朵是缓慢的……（莎士比亚《理查三世》第二幕第四场）生物的生活方式千差万别。例如，众所周知，蜉蝣成年后只存活和繁殖一天，而海龟则存活和繁殖几十年。然而，越来越清楚的是，来自同一物种的雄性和雌性在这些生活史上也可能表现出惊人的差异，并且可能在寿命、生长速度和繁殖持续时间上有所不同。人们认为，男性和女性对不同生活史的表达可以提高两性的繁殖成功率。这种现象的最终原因源于两性在生殖投资方面的根本差异，女性通常会在更少、更大的卵子上投入更多，而男性则会在数量更多的精子上投入较少。这种基本差异所产生的结果是深远的，并决定了两性在一生中取得繁殖成功的不同方式。例如，据预测，雄性之间会为获得交配和受精的机会而激烈竞争。这可能导致一种高风险/高回报的“活得快，早死”策略，这种策略需要精力充沛，因此需要高碳水化合物(C)饮食。另一方面，预计雌性将受益于采用“慢生老”策略，该策略取决于获得高蛋白(P)，以支持高繁殖力和促进生存。实验与这一观点一致，但令人惊讶的是，我们对整个生命周期中饮食对性别特异性反应对生殖成功率的影响知之甚少。我们也不知道男女对饮食的反应有何不同。我们在这项研究计划中的目标是解决这些主要差距。实现后续步骤的一个主要问题是缺乏急需的直接实验测试的模型系统和操作。幸运的是，果蝇模型系统与“营养几何”（以精确的C:P比例配制的饮食）的最新进展相结合，为解决这一差距提供了强有力的工具。例如，我们可以在整个生命过程中以确定的方式改变饮食，为高分辨率的生存和繁殖成功率测试产生大量队列，并使用遗传和分子遗传试剂来测试操纵营养感知途径的影响。此外，我们在许多代中进化出了不同磷和碳比例的果蝇种群，这为研究这些饮食是否分别有利于雌性和雄性的成功提供了一个独特的机会。我们的首要目标是确定对饮食反应的性别差异是如何以及为什么发生的，具体如下：我们将测试在发育和成年期间不同饮食对雄性和雌性繁殖成功率的直接影响。我们将使用不同的C:P比率来操纵饮食，并分别测试对每种性别的寿命和繁殖成功率的影响。我们将研究与性别特异性反应相关的机制。在这项研究中，我们将使用分子和遗传工具来测量营养感知途径的改变对雄性和雌性繁殖成功率的影响。我们将从具有高和低C和p暴露的进化史的系中测量雄性和雌性的繁殖成功率，这将检验男性和女性成功的平衡已经进化的观点。对营养感知基因表达的测试也将揭示这些潜在途径的进化变化。这项工作将首次直接测试在整个生命过程中对饮食反应的性别差异的影响和机制。这项工作有望使我们对男性和女性为何以及如何表现出不同的生活史的基本理解取得重大进展。

'..methinks I would not grow so fast, Because sweet flowers are slow ...' (Shakespeare, Richard III, Act II Scene 4)There is huge variation in the way that organisms live their lives. For example, mayflies famously live and reproduce as adults for only 1 day, while turtles live and reproduce for many decades. However, what is becoming increasingly clear is that males and females from the same species can also exhibit striking variation in these life histories, and may differ in lifespan, growth rate and duration of reproduction.It is thought that the expression of contrasting life histories by males and females allows each sex to increase their reproductive success. The ultimate reasons for this stem from fundamental differences between the sexes in reproductive investment, with females typically investing more in fewer, larger eggs and males less in their more numerous sperm. The consequences that flow from this basic difference are profound and dictate the contrasting ways in which each sex achieves reproductive success over their whole lifetimes.For example, males are predicted to compete strongly with each other for access to matings and fertilisations. This can lead to a high risk / high pay off 'live fast die young' strategy that is energetically demanding and hence requires a high carbohydrate (C) diet. On the other hand, females are expected to benefit from adopting a 'live slow die old' strategy contingent on the acquisition of high protein (P) to support high fecundity and promote survival. Experiments are consistent with this idea but we have surprisingly little insight into the effects on reproductive success of sex-specific responses to diets across the whole lifespan. Nor do we understand how each sex responds differently to diet. Our aim in this research programme is to address these major gaps.A major problem in achieving the next steps has been a lack of model systems and manipulations for the direct experimental tests that are urgently needed. Fortunately, the fruit fly model system, in combination with recent advances in 'Nutritional Geometry' (diets formulated with precise ratios of C:P) offer powerful tools to address this gap. For example, we can vary diets across the life course in a defined manner, generate large cohorts for high-resolution tests of survival and reproductive success and use genetic and molecular genetic reagents to test effects of manipulating nutrient sensing pathways. In addition, we have evolved populations of flies on different P and C ratios over many generations, which offers a unique opportunity to examine whether these diets favour the success of females versus males, respectively. Our overarching aim is to identify how and why sex differences in responses to diets occur, as follows:1. We will test the direct effect on the reproductive success of males and females of varying diets during development and adulthood. We will manipulate diets with varying C:P ratios and test the effect on lifespan and reproductive success for each sex separately.2. We will investigate the mechanisms associated with the sex-specific responses. In this we will use molecular and genetic tools to measure the impact of altered nutrient sensing pathways on male and female reproductive success.3. We will measure the reproductive success of males and females from lines with an evolutionary history of exposure to high and low C and P. This will test the idea that the balance of male to female success has evolved. Tests of the expression of nutrient sensing genes will also reveal evolved changes in these underlying pathways.The work will provide the first direct tests of the consequences and mechanisms underpinning sex differences in responses to diet across the whole life course. The work is expected to result in a major advance in our fundamental understanding of why and how males and females exhibit different life histories.