Food availability affects behavior but not circulating gonadal hormones in maternal Belding's ground squirrels.

ABSTRACT

We tested predictions of hypotheses suggesting that the steroid hormones, testosterone (T), progesterone (P), and estradiol (E2), contribute to the energetic regulation of behaviors associated with rearing young in free-living female Belding's ground squirrels (Spermophilus beldingi). We provisioned some female S. beldingi with food rich in fat and calories, and used unprovisioned females as controls. We observed the behavior of females throughout the reproductive cycle, and regularly collected blood samples to measure plasma hormone concentrations. Circulating concentrations of T, P, and E2 were similar in provisioned and unprovisioned females, as were temporal patterns of variation in these hormones. Peaks in rates of nest maintenance and aggressive behavior occurred during gestation and were associated with elevated concentrations of circulating T, P, and E2, raising the possibility that one or more of these hormones mediates behaviors that help females establish maternal nest sites and territories after mating. Temporal patterns of variation in behavior were similar among provisioned and unprovisioned females; however, rates of resting, vigilance, and aggression were higher among provisioned females, whereas unprovisioned females devoted significantly more time to feeding and locomotion. Thus, our data suggest that in maternal S. beldingi, gonadal steroids play a role in mediating behavior associated with raising offspring, but do not facilitate changes in rates of behavior associated with increased energy availability.