Causes and consequences of variation in maternal effects in the wild

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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.