90.2 Friday, Jan. 6 Building better babies: Impact of individual variation in milk composition on differential reproductive performance of Columbian ground squirrels SKIBIEL, A.L.*; HOOD, W.R.; Auburn University; Auburn University email@example.com
In mammals, maternal care is an integral part of a species life history strategy and variation among females in maternal effort provides the raw material upon which natural selection can act. Consequences of variation among females in size and reproductive timing on offspring mass and survival are ubiquitous in the literature, but the underlying link between maternal traits and reproductive performance is poorly understood. Mammals have a protracted period of offspring dependence during the lactation period; thus, differential reproductive performance is likely to occur through variation among females in lactation performance, such as milk composition. The objectives of this study were to examine impacts of maternal size, condition, and reproductive timing on milk composition and to determine if variation among females in milk composition contributes to variation in weaning mass, growth and differential survival of offspring. Females differed in the proximate composition of milk, gross energy, proportion of energy from proximate constituents, and milk sodium and potassium concentrations. Maternal condition and size did not impact milk composition whereas parturition date had a significant curvilinear relationship with milk lipid concentration, gross energy, and the proportion of energy from lipids. Carbohydrate and potassium concentrations in milk had a positive effect on weaning mass and growth rate. Probability of over-winter survival was greater for pups receiving milk higher in lipids, gross energy, potassium, and a higher proportion of energy from protein and lipids. These results indicate that reproductive timing is an important factor influencing milk composition and thus juvenile survival in this species.