Abstract
Parental investment theory predicts that observed levels of parental care afforded to offspring are set by the benefits (to offspring quality and survival), relative to the costs (to parental survival or future reproduction). Although difficult to document, there is often substantial individual-variation in the amount of parental care within species. We measured the impact of individual variation in maternal care on fitness in a wild population of North American red squirrels (Tamiasciurus hudsonicus). We used pup retrieval latency following a nest intrusion as a measure of maternal motivation to care for pups. Pups from large litters grew faster if they had a highly motivated mother, indicating that maternal motivation can mitigate the trade-off between litter size and offspring growth. Pups whose mothers who returned to the nest faster were more likely to survive to autumn, a critical life history stage. These results highlight important fitness impacts of having a highly motivated mother and show that maternal motivation can alter a fundamental life history trade-off between offspring quantity and quality.
