Early-life adversity and the role of habitat: Consequences for females growing up in a marginal environment

Early-life adversity has life-long consequences on physiology, behavior, survival, and fitness. It is fundamentally influenced by habitat quality in the pre-adult developmental environment. Suboptimal habitat has impacts at the individual level, and if it affects all animals similarly in that habitat, at the population level. Columbian ground squirrels (Urocitellus columbianus) are herbivores that survive winter by hibernating for 8-9 months each year. Females are highly philopatric - living and reproducing in the same area in which they were born. Critical in preparing for hibernation in summer is foraging to accumulate sufficient body fat levels from forage, especially polyunsaturates. These are found in forbs, but not in grasses with their high structural cellulose. Using a hormonal-challenge protocol, we tested the hypothesis that females of all ages living in a human-altered low-quality meadow with an abundance of grasses would be in poorer condition than those living in a high-quality natural meadow with an abundance of forbs. Females of all ages on the low-quality meadow had lower body masses, lower hematocrit levels, higher neutrophil:lymphocyte ratios, a stress axis that was less tightly regulated, and energy mobilization that was more poorly regulated than those on the high-quality meadow. Yearlings and young adults on the low-quality meadow showed reduced ability to mobilize free fatty acids, possibly related to lower endogenous levels. Overwinter survival of juveniles was significantly lower on the low-quality meadow, but that in the older age classes was similar on the two meadows. We conclude that female Columbian ground squirrels likely experience life-long, negative consequences from living in human-caused, low-quality habitat and that related scuirids may be similarly affected by such habitat changes.