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Reproduction in the Face of Stress: Mediation by the Hypothalamic-Pituitary-Adrenal (HPA) Axis


Stress and glucocorticoids are hypothesized to mediate a trade-off between current and future reproduction, as organisms are predicted to invest less in current reproduction under stressful conditions. In this dissertation I explored whether stress and activation of the hypothalamic-pituitary-adrenal (HPA) axis (resulting in elevated glucocorticoid concentrations) suppress current reproductive behavior in the monogamous, biparental California mouse ( Peromyscus californicus). Initially, I characterized HPA function under baseline and post-stress conditions (Aim 1). I next tested the hypotheses that older animals are more stress-resistant than younger animals, as older animals have lower residual reproductive value (Aim 2), and that fathers are more stress-resistant than non-fathers (Aim 3). Lastly, I determined whether chronic stress (Aim 4) and acute glucocorticoid elevation, separate from external stress (Aim 5), would decrease paternal care and alter survival and development of offspring. Results demonstrate that HPA function in California mice differs markedly from that of previously studied rodents (Aim 1), and that changes in residual reproductive value (age; Aim 2) and reproductive status (Aim 3) do not modulate HPA axis activity. Chronic stress reduced paternal behavior (Aim 4), but effects were subtle and not likely mediated solely by changes in circulating corticosterone levels, as corticosterone injection did not alter paternal behavior (Aim 5). Moreover, decreased paternal behavior during chronic stress did not appreciably alter survival, development, growth or HPA function of pups, suggesting that stress-induced decreases in paternal care had no fitness consequences under controlled laboratory conditions. In conclusion, glucocorticoids do not appear to directly mediate the trade-off between current and future reproduction in males of this species; however, stress can decrease paternal behavior. Therefore, while corticosterone concentrations may serve as part of the signal by which parents determine reproductive investment, increases in this hormone alone may not be sufficient to derail current reproductive attempts. Instead, stress-induced changes in other hormones and neuropeptides might be important in regulating stress-related changes in behavior. These experiments provide important insight into interactions between reproductive status and HPA function in a biparental mammal, and could have implications for conservation of biparental species and for understanding effects of stress on human parenting.

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