UC Riverside

ABSTRACT OF THE DISSERTATION

Placentophagia in the California Mouse (Peromyscus californicus): Causes and Consequences

by

Juan Pablo Perea-Rodriguez

Doctor of Philosophy, Graduate Program in Evolution, Ecology, and Organismal Biology

University of California, Riverside, June 2016

Prof. Wendy Saltzman, Chairperson

Male parental care, in contrast to maternal care, is uncommon in mammals, with an estimated 10% of species showing some level of male involvement in the raising of their young. Because males do not gestate or lactate, it is noteworthy that some of the same endocrine mechanisms underlying maternal care have been linked to the onset and maintenance of paternal care. In some biparental mammals, such as the monogamous California mouse (Peromyscus californicus), fathers, in addition to mothers, ingest placenta during the birth of their young. Still unknown, however, are the factors that activate placentophagia in males, as well as its functional consequences, if any. Especially intriguing is the possibility that placentophagia by males might modulate parental responsiveness, as reported in females. Thus, my dissertation investigated the possible facilitating role of male placentophagia in the expression of paternal behaviors, as well as the effects of mate-related stimuli on attraction to newborns and/or placenta.

The first experiment investigated possible influences of reproductive condition on placentophagia by determining the prevalence of placenta ingestion by males that were virgins, first-time expectant fathers, or experienced fathers. The second and third experiments were designed to determine possible neural, affective, and/or behavioral changes in male mice induced by oral administration of placenta. Finally, the fourth experiment investigated possible effects of chemical signals in excreta of gestating females on males’ attraction to pups and placenta. I hypothesized that placentophagia would be more prevalent in parents, that placenta administration would lead to physiological, emotional, and behavioral changes that positively correlated with a males’ parental responsiveness, and that exposure to excreta from a gestating female would increase the prevalence of placentophagia by virgin males.

These studies revealed that male California mice are more likely to ingest placenta when their mates become pregnant and/or with reproductive experience; however, these effects do not appear to be mediated exclusively by chemical cues from female excreta. They further indicate that placentophagia by males leads to decreased neophobia and/or anxiety. Together, these studies suggest that placentophagia may be an important component of males’ transition to fatherhood in biparental mammals.