Causes and consequences of variation in maternal effects in the wild

生命早期所经历的条件对个人健康有很大的影响。这些早期生活影响的一个重要来源是产前和产后母亲护理的变化——因此，“母亲效应”被定义为母亲的表型对其后代表型的影响，而不是遗传自她的基因的直接影响。母系影响的差异可能很大，至少与环境或个人自身基因的影响一样大。然而，与实验室或农场种群相比，对这些影响的自然调查少得惊人，因此它们的重要性和进化后果尚未得到充分评估；如果这些母性影响是遗传的，那么它们可能是制约进化的主要因素。在这项研究中，我们将调查母性影响的原因和后果，对苏格兰朗姆酒岛的马鹿进行单独监测。这是一个特别合适的研究群体，因为雄性不参与亲代照顾，而雌性在漫长的一生中生育许多幼崽。在这个群体中，母亲对后代性状的影响是众所周知的；结合完整的家系信息、高密度基因分型数据和生活史数据，该系统是表征母体遗传对后代表型影响的大小、方向和基因组位置的绝佳候选。首先，我们的目标是估计由不同类型的母体效应解释的一系列性状的变化，如出生体重和幼崽存活率：永久性环境效应，如由于母亲自己的养育条件造成的影响，以及由于母亲之间的加性遗传变异造成的影响（即可以响应方向选择的遗传变异）。其次，我们将确定这些母性影响在多大程度上与小牛的性别、母亲的生殖状况、怀孕期间的环境条件和母亲的年龄有关。一般来说，我们预计随着所需投资的增加（生儿子比生女儿更昂贵）或条件的恶化，母性效应的差异会增加，但反过来也有可能。第三，我们将利用项目期间获得的早期乳汁质量、寄生虫负荷和抗体产生的新表型，从粪便和新生儿血液样本中非侵入性地估计，来研究我们可以在多大程度上解释早期记录的母体效应。第四，我们将使用基因组信息来研究母体遗传效应的基因组定位，首先依次考虑每条染色体（染色体分配），然后考虑每条染色体的较小区域（区域遗传力，全基因组关联）。我们建议的最终目的是解决进化研究中的一个主要难题。在大多数被测量的情况下，自然选择倾向于较大的体型，大多数体型特征是遗传的，然而物种不会随着时间的推移而改变体型。解释这种停滞的一个假设是，母亲的遗传和选择产生了限制。因此，母亲的基因可能独立于后代的基因影响后代的体型（母体加性遗传效应），并且在母体的遗传效应和后代自身对某一性状的遗传效应之间可能存在负遗传相关。这种遗传相关性是否作为一种进化约束，关键取决于选择的强度和方向，以及对后代性状和母亲在这一性状上的表现。我们打算首次在自由生活的种群中测量所有必要的参数，以测试进化约束的预测。

Conditions experienced during early life can have large impacts on individual fitness. An important source of these early life effects is variation in pre- and postnatal maternal care - hence 'maternal effects', defined as the influence of a mother's phenotype on the phenotype of her offspring over and above the direct effect of genes inherited from her. Variation in maternal effects can be large, at least as large as that due to influences of the environment or of an individual's own genes. However, there are strikingly few investigations of these effects in natural as opposed to laboratory or farm populations and so their importance and evolutionary consequences have not been fully assessed; if these maternal effects are genetic in origin, they could be a major source of constraint in evolution. In this study we will investigate the causes and consequences of maternal effects in the individually-monitored red deer of the Isle of Rum, Scotland. This is a particularly appropriate study population as males play no part in parental care, whilst females produce many calves over long lifetimes. Maternal effects on offspring traits are known to be large in this population; combined with complete pedigree information, high density genotyping data and life history data, this system is an excellent candidate for characterising the magnitude, direction and genomic location of maternal genetic effects on offspring phenotype.Our aims are first, to estimate the variation in a range of traits such as birth weight and juvenile survival that is explained by different kinds of maternal effects: permanent environment effects such as those due to a mother's own rearing conditions and those due to additive genetic variation between mothers (i.e. genetic variation that can respond to directional selection). Second, we will determine the extent to which these maternal effects vary (interact) with the sex of the calf, the reproductive status of the mother, environmental conditions during pregnancy and the mother's age. Generally we expect maternal effects variance to increase as the investment required gets greater (sons more costly than daughters) or the conditions get tougher, but the reverse is also possible. Third, we will use new phenotypes obtained during the project for early milk quality, parasite load and antibody production, estimated non-invasively from faecal and neonatal blood samples, to investigate the extent to which we can explain the maternal effects documented earlier. Fourth, we will use genomic information to investigate the genomic location of maternal genetic effects, first by considering each chromosome in turn (chromosome partitioning), then by considering smaller regions of each chromosome (regional heritability, genome-wide association).The final and ultimate aim of our proposal is to address a major puzzle in evolutionary research. In most cases where it has been measured, natural selection favours larger body size, and most body size traits are heritable, and yet species do not change body size over time. One hypothesis explaining this stasis is that there are constraints arising from the genetics of and selection on mothers. Thus, a mother's genes may affect offspring body size independently of the offspring's genes (maternal additive genetic effect) and there may be a negative genetic correlation between the maternal genetic effect and the offspring's own genetic effect on a trait. Whether this genetic correlation acts as an evolutionary constraint depends critically on the strength and direction of selection on both the offspring trait and maternal performance for this trait. We intend to measure all the parameters required to test the prediction of evolutionary constraint for the first time in a free-living population.