Maternal influences on reproduction in two populations of Columbian ground squirrels

Abstract

In this study, we examined influences of maternal traits on offspring birth mass, growth rate, and weaning mass for two populations of Columbian ground squirrels (Spermophilus columbianus). We tested relationships between maternal body condition, structural size, change in mass (during gestation, during lactation, and during the entire reproductive period), timing of reproduction, and litter size on offspring traits using path analyses. To assess whether maternal investment in offspring traits extended beyond the period of direct maternal care, we examined associations between offspring traits and overwinter survival of pups. In general, females in better condition raised pups that were heavier at weaning and that had faster growth rates during lactation. Litter size had a negative effect on mass and growth rate, and only litter size had a significant effect on birth mass. For both populations, the average weaning mass of pups within a litter had a positive effect on the number of pups that survived to yearling age. In a population for which birth masses and growth rates were available, pups with faster growth rates survived better to yearling age, whereas birth mass had no effect on the number of surviving offspring in litters. We found substantial maternal influences on offspring growth and size, and evidence that these influences may extend beyond the juvenile period and constitute influences on fitness. The key to arriving at these conclusions was to take the number of offspring into account before testing for maternal effects.

Milk matters: offspring survival in Columbian ground squirrels is affected by nutrient composition of mother's milk

“…Litter birthdate (day of the year; 1 January = day 1) was used as a measure of reproductive timing. Maternal body condition at spring emergence was estimated by extracting the residuals from the regression of spring emergence body mass on zygomatic arch breadth (Dobson et al, 1999;Georges et al, 2001;Schulte-Hostedde et al, 2005;Skibiel et al, 2009). Measures of offspring performance included offspring body mass at weaning, growth rate during the lactation period and survival overwinter.…”

“…Separate models were run for each milk component. Because litter size at weaning is significantly negatively correlated to offspring weaning mass and growth rate in this population (Skibiel et al, 2009), litter size was included as a covariate in the models. Dam ID was included as a random effect to account for the multiple pups per dam.…”

“…The reproductive performance of mothers, measured as offspring growth, offspring mass, litter size, or offspring survival, has been shown to vary with maternal characteristics, such as age, parity, body condition, and body size, as well as reproductive timing (Clutton-Brock et al, 1982;Hoogland, 1995;Skibiel et al, 2009). Larger females in better condition tend to invest more resources into reproduction (Price, 1998;Broussard et al, 2005), either producing more young or heavier individual young.…”

“…Indeed, previous studies of Columbian ground squirrels have shown that maternal body size and body condition, as well as reproductive timing, impact reproductive performance (King et al, 1991;Dobson et al, 1999;Skibiel et al, 2009). Larger mothers in better condition produce either more young or young that are heavier and grow faster during the lactation period (King et al, 1991;Dobson et al, 1999;Skibiel et al, 2009), and mothers that reproduce earlier have more of their young survive hibernation (Dobson et al, 1999). If these relationships are mediated through the nutritive properties of mother's milk, the levels of milk protein and fat and milk energy density should be particularly important for offspring growth and survival.…”

Determinants of lifetime reproduction in female brown bears: early body mass, longevity, and hunting regulations

“…As reported in red squirrels Tamiasciurus hudsonicus (Descamps et al 2008), this correlation suggests a ''silver-spoon effect'' (Grafen 1988) in female brown bears. Similarly to other mammals, larger mothers have larger offspring (e.g., Clutton-Brock et al 1988, Wauters et al 1993, Skibiel et al 2009). In addition, larger female yearling brown bears establish their home range closer to or within their natal home range, which probably gives them a reproductive advantage through familiarity with the area and better access to resources facilitated by their mother (Zedrosser et al 2007b).…”