Estradiol and estrogen receptor α in the mPOA and MeA in dwarf hamster (Phodopus campbelli) fathers.

E2 and its alpha receptor (ERα) have an essential role in the regulation of maternal behavior. In dwarf hamster (Phodopus campbelli), E2 facilitates the display of paternal care, and it is possible that ERα is part of the neuroendocrine mechanisms that regulate this behavior. The aim of this study was to analyze the influence of copulation, cohabitation with the pregnant mate and the presence of the pups on paternal behavior, circulating E2 levels and the presence of ERα in the medial preoptic area (mPOA) and medial amygdala (MeA) in dwarf hamsters. Eight males were mated with intact females (IFs), 8 with tubally ligated females (TLFs) and 8 with ovariectomized females (OFs). In males mated with IFs, paternal behavior tests were performed after copulation, halfway through pregnancy and 24 h after the birth of their pups. Males mated with TLFs were subjected to paternal behavior tests at equivalent periods as the males mated with IFs. In males mated with OFs, paternal behavior tests were performed on days 1, 5 and 10 of cohabitation. After the last paternal behavior tests, blood samples were taken for quantification of E2 by radioimmunoassay (RIA), and the brains were dissected to determine ERα immunoreactivity (ir) in the mPOA and MeA. Fathers mated with IFs had higher serum E2 concentrations and more ERα-ir cells in the mPOA than those of males mated with TLFs and OFs. These results suggest that E2 and its ERα may be associated with paternity in the dwarf hamster.

Resting Metabolic Rate Is Positively Correlated with Parental Care Behavior in a Dwarf Hamster.

Endotherms maintain high and constant body temperatures through the production and maintenance of metabolic heat. Defining the evolutionary history of these thermal adaptations and the selective factors responsible for the evolution of endothermy despite its high metabolic costs have been elusive and controversial topics in evolutionary biology. In this sense, several models have been proposed to explain the evolution of endothermy. Among them, the parental care model explains the increase in resting metabolic rate (RMR) by the action of natural selection favoring parental care. Thus, a positive relationship between parental care behavior and RMR is predicted. However, there appears to be no or little previous work experimentally testing this relationship. In the study presented here, RMR was increased through l-tyrosine injections and parental care behavior was measured. This treatment allowed us to test the relationship between RMR level and parental care behavior in a dwarf hamster. It was found that increased RMR enhanced male parental care. Specifically, male latency time, or the time until contacting and picking up their pups, decreased when RMR increased. This study demonstrates the positive relationship between RMR and the allocation of resources to parental care. This study supports the main assumption of Kotejas's parental care model and accepts Koteja's proposed explanation for the evolution of endothermy as a plausible hypothesis.