The interaction between personality, offspring fitness and food abundance in North American red squirrels.

Animal personality is now frequently reported in wild and captive populations. It has been shown to be moderately heritable and to have potentially important fitness consequences. Variation in personality within a population may be maintained by balancing selection if different values of personality traits are favoured under different conditions. We measured personality in 98 female North American red squirrels (Tamiasciurus hudsonicus Erxleben), and examined whether its variation could be maintained by changing selection pressures acting via reproductive traits and yearly variation in food abundance. There was no effect of personality on parturition date or litter size, but a female's activity was correlated to the growth rate of her offspring in the nest, and her aggressiveness was correlated to their survival in the nest and overwinter. The magnitude and direction of the effects changed among life history stages and years, possibly in association with food supply in some cases, and may indicate a role for balancing selection in the maintenance of personality.