The quality of parental care influences offspring fitness. In domesticated laboratory rodents, pups that have chronically stressed mothers receive low quality care, leading pups to develop highly reactive stress responses. Affected pups will have high stress hormone levels as adults, which can have severe consequences on their future survival and reproductive output. This research examines the relationship between stressed mothers, poor maternal care, and the offspring stress response and survival in the degu (Octodon degus), a wild, free-living rodent. Degus practice a unique reproductive tactic called "plural breeding with communal care" where multiple mothers cooperate to raise each other's pups. This research also will ask whether this unique social strategy can buffer the offspring against post-natal stress. By manipulating the stress levels of mothers and measuring stress hormone levels in pups in both field and laboratory experiments, this research will provide a comprehensive description of the links between stress, development, and, ultimately, survival. This link has never been demonstrated in a wild, free-living rodent. This research will have broader impacts because it will address the link between parental care and offspring survival, which is a major unsolved problem in ecology and stress physiology. Further broader impacts of this research will include scientific outreach through a weekly blog that is incorporated into the curriculum of an undergraduate course, presentations to senior citizens and middle/high school girls, undergraduate research opportunities, and support for a young scientist completing her PhD research.
Conditions during early life are important for shaping the physiology and behavior of young animals. Maternal care in particular has been shown to affect several aspects of offspring’s future fitness. In domesticated laboratory rats and mice, it has been shown that the pups receiving low quality care from their mothers will develop hyper-reactive stress responses. These stress responses are characterized by high levels of stress hormones in response to stressors that also take a long time to get back down to baseline levels. This increased total exposure to stress hormones can negatively impact the future survival and reproductive success of these animals. In order to determine that the relationships described above are not just particular to domesticated rats and mice, we used a different model organism called the degu (Octodon degus) in order to determine whether the quality of maternal care affects the development of the offspring stress response. Degus are rodents endemic to Chile that practice a unique reproductive tactic called "plural breeding with communal care" where multiple mothers cooperate to raise each other’s pups. An additional aim of this research was to determine whether this social reproductive strategy can act as a buffer against post-natal stress. Because results from the laboratory cannot always be extrapolated to the real world, we carried out similar experiments using both captive degus in the laboratory and wild degus in the field. From 2011-2013, we traveled to Chile three times to work with degus in both the laboratory and the field. We manipulated the stress hormone levels of degu mothers by implanting stress hormone pellets and we later measured the stress responses of the pups. We found that stressed mothers performed lower rates of maternal care and that this significantly affected the stress responses of pups both in the lab and the field. While the stress responses of the lab and field pups were similar, the components of the stress response affected by maternal care were different than those of the rats and mice described earlier. This suggests that maternal care significantly affects development of the stress response in rodents in general, but that the ways in which maternal care affects this development can differ by species. We also found that plural-breeding with communal care can help mitigate some of the effects of maternal stress on the development of the offspring stress response. This may help explain the evolutionary significance of this unique, reproductive tactic. Further broader impacts of this study include a scientific blog written by one of the co-PIs. This blog was written for a general audience and was viewed over 7,000 times over the last few years by a wide audience. This research also provided research opportunities for six different undergraduates, several of whom were women or targeted minorities. Finally, this research helped a young scientist complete her dissertation research.
