Phylogenetic analyses of parental conflict in birds

男性和女性在生育问题上经常有分歧。雌性产生少量但较大的配子（卵子），而雄性产生许多小配子（精子）。因此，雌性限制了有性繁殖物种的繁殖率。因此，雌性能生育的后代数量取决于它能产下的卵的数量，而雄性能生育的后代数量取决于它能使多少雌性受精。这种最优交配策略的分歧是性冲突的基础。增强一种性别的繁殖潜力的适应可能对另一种性别有害，并且预计会导致弱势性别的反适应。性别之争是一种普遍存在的进化力量。最近的研究表明，性冲突会导致对最佳交配条件的分歧，从而引发两性之间的追逐战。这种斗争可以推动形态和行为特征的快速进化，从而导致生殖行为和解剖结构的多样化。两性之间的军备竞赛也可能产生代价，可能损害它们适应环境变化的能力。因此，性冲突对繁殖策略、物种形成和灭绝具有重要意义。然而，性别冲突可能不会在受精时结束，因为父母的照顾是昂贵的，所以父母通常通过让配偶承担抚养孩子的艰苦工作来做得更好。然而，父母冲突的进化后果在很大程度上被忽视了。物种统计比较和系统发育重建（类似于家谱）的最新进展，以及鸟类自然行为和生态数据的快速积累，现在使我们能够使用强大的统计分析来测试性冲突理论的预测。我们将在主要鸟类谱系中检验四种主要假设。1. 什么因素限制了父母之间的冲突？如果幼崽的需求很高，或者父母双方的交配机会有限，父母就会合作抚养幼崽。我们将通过比较对幼鸟和交配机会有不同要求的鸟类群体中父母冲突结果的变化来验证这些预测。2. 男性和女性是否表现出一种进化上的关爱拉锯战？如果雄性抛弃了自己的后代，雌性是否会补偿并加强照顾以弥补不足，还是会失去后代？我们还将使用最新的统计方法来测试是雄性还是雌性驱动了性别之争，该方法可以检测在进化过程中，一种特征的变化是否更有可能在另一种特征的变化之前发生。3. 性冲突会导致快速进化吗？我们将测试性冲突强度的变化是否与交配行为（鸣叫和雄性展示飞行）、形态（羽毛颜色、装饰和两性大小二态性）和生活史（繁殖率和存活率）有关。4. 最后，我们将测试亲代冲突对物种丰富度和灭绝的影响。在照顾鸟类方面的激烈性冲突是否与拥有异常多物种的鸟类有关？两性之争是否增加了物种灭绝或数量下降的风险？这个提议代表了（据我们所知）第一个主要的系统发育倡议，揭示了父母冲突作为一种潜在的普遍进化力量的影响。我们预计，我们的研究结果将确定性别冲突对交配策略和性状进化速度的影响，并确定关爱冲突是否会驱动物种丰富度和灭绝风险。因此，我们的工作不仅将有助于进化生态学（性冲突理论）的核心主题，而且将推进我们对社会行为，生活史理论和保护生物学的理解。

Males and females often disagree over reproduction. Females produce few but large gametes (eggs), whereas males produce many small gametes (sperm). Females therefore limit the reproductive rate in sexually reproducing species. As a consequence, the number of offspring a female can have depends on the number of eggs that she can produce, but the number of offspring a male can sire depends on how many females he can fertilize. This divergence of optimal mating strategies is the basis of sexual conflict. Adaptations that enhance the reproductive potential of one sex may be detrimental to the other sex, and are expected to drive counter-adaptations by the disadvantaged sex. The battle of the sexes is a pervasive evolutionary force. Recent studies suggest that sexual conflict results in disagreements over mating optima that trigger a chase-away battle of the sexes. This battle can drive the rapid evolution of morphological and behavioural traits, and consequently result in diversification in reproductive behaviour and anatomy. The arms race between the sexes may also incur costs that may compromise their ability to adapt to environmental changes. Thus, sexual conflict has major implications for breeding strategies, speciation and extinction. The conflict of sexes, however, may not end at fertilisation, since parental care is costly so that parents often do better by making their mate do the hard work of raising young. The evolutionary consequences of parental conflict, however, have been largely neglected. Recent advances in statistical comparisons of species and in phylogenetic reconstructions (akin to family trees), and the rapid accumulation of data on natural behaviour and ecology of birds now allow us to test predictions of sexual conflict theory using powerful statistical analyses. We will test four major hypotheses across and within major bird lineages. 1. What factors limit parental conflict? The parents are expected to cooperate in raising young if the demands of the young are high, or the mating opportunities of both parents are limited. We will test these predictions by comparing variation in the outcomes of parental conflict in groups of birds that have different demands of the young and mating opportunities. 2. Do males and females exhibit an evolutionary tug-of-war over care? If the male deserts the brood, does the female compensate and intensify her care to meet the shortfall, or do the offspring lose out? We will also test whether males or females drive the battle of the sexes using a recent statistical approach that can detect whether changes in one trait were more likely to occur before changes in a different trait over evolutionary time. 3. Does sexual conflict result in rapid evolution? We will test whether variation in the intensity of sexual conflict is associated with mating behaviours (song and male display flights), morphology (plumage colour, ornaments and sexual size dimorphism), and life-histories (reproductive rate and survival). 4. Finally, we will test the consequences of parental conflict on species richness and extinction. Is intense sexual conflict over care associated with bird families that harbour unusually high numbers of species? Does the battle of the sexes increase the risk of extinction or population declines? This proposal represents the first (to our knowledge) major phylogenetic initiative to unravel the influence of parental conflict as a potentially pervasive evolutionary force. We anticipate that the outcomes of our research will identify the effects of sexual conflict on mating strategies and rates of trait evolution, and determine whether conflict over care drives species richness and risk of extinction. Thus, our work will not only contribute to a core topic in evolutionary ecology (sexual conflict theory) but will also advance our understanding of social behaviour, life-history theory and conservation biology.