Phodopus campbelli is a naturally biparental dwarf hamster with males so paternal they will act as midwives during the birth of their litter. The hormonal regulation of parental behaviour has been well established in many species. However, to date, no causal mechanism for the extensive paternal behaviour displayed by male P. campbelli has been discovered. Recently, activity at the progesterone receptor has been shown to inhibit infant-directed behaviour in male mice. Therefore, the first study in this thesis was carried out to determine if antagonism of the progesterone receptor (PR) would enhance infant-directed care behaviour in naïve P. campbelli males. Despite detectable serum progesterone concentration in males, PR antagonism did not alter progesterone concentration, nor did it alter infant-directed behaviour in males with antagonized PR in adulthood. A slight increase in the latency to retrieve a pup seen in males with antagonized PR during adolescence suggests that there may be a developmental effect of PR activity on infant-directed behaviour in adulthood. Neonatal male rats express high levels of PR in brain regions important for parental behaviour. Since hormones can act very early in life to organize adult behaviour, the second study was carried out to determine if progesterone acting much earlier than adolescence is important in the regulation of paternal behaviour in P. campbelli adulthood. Males were treated daily for the first week of life with transdermal progesterone, which increased neonatal serum progesterone concentration fivefold. Despite the significant increase in progesterone (and therefore presumably activity at the PR), male behaviour in three different stages of adulthood (sexually naïve, during the birth of the male’s first litter, and in new fatherhood) towards pups was not altered. Measures of paternal contribution such as pup weight throughout the lactational period were altered by progesterone treatment during the neonatal period, but litter quality was ultimately high in both groups. Therefore, activity at the PR in adulthood, puberty, or during the neonatal period does not inhibit paternal behaviour in the naturally biparental hamster, P. campbelli. Thus, progesterone and its receptor do not organizationally or activationally regulate paternal behaviour in P. campbelli. / Thesis (Master, Biology) -- Queen's University, 2009-09-04 13:23:18.733

Doctor of Philosophy / Department of Psychology / Jerome Frieman / The present experiment investigated whether dwarf hamsters (Phodopus campbelli) demonstrate temporal discounting. This was investigated by comparing the behavior of dwarf hamsters and Sprague-Dawley rats (Rattus norvegicus) in an adjusting delay procedure and applying the theory of behavioral economics to explain the resulting behavior. Dwarf hamsters demonstrated temporal discounting and tolerated longer delays than did the more impulsive rats. There was not a statistically significant difference between these species concerning indifference points. There was a statistically significant difference in the slopes of their discounting functions and the delay at which the end criterion was met. Neither species exhibited sex differences with respect to these measures nor with storage of food. There were a number of differences between the species. Rats started responding quickly, whereas dwarf hamsters waited significantly longer. When faced with increasing delays, rats increased the number of pellets earned while dwarf hamsters earned the same amount. Finally, rats lost weight throughout the experiment while dwarf hamsters gained weight. There were also a number of similarities. When faced with an increasing delay, both rats and dwarf hamsters increased the number of responses made, and increased the number of times they timed out on Larger Later trials. Some of these findings disagree with previous research and predictions of the behavioral economic theory of demand, creating a need for further research.

Master of Science / Department of Psychology / Jerome Frieman / Male and female Phodopus campbelli were investigated for kin recognition abilities, assessed by kin discrimination of bedding, urine, fecal, or midventral glandular secretion odors. Using a habituation-discrimination paradigm, subjects were presented either the odors of a pair of their own brothers (C[subscript 1]) or a pair of brothers that were unrelated to them (C[subscript 2]). All subjects were then presented with a final test discrimination odor from a male donor unrelated to themselves or the first donors. All subjects differentiated between the bedding and glandular odors of two unrelated males, regardless of condition assignment. Subjects did not statistically differentiate between the odors of two brothers. These results suggest Phodopus campbelli are capable of recognizing kin based on bedding and midventral gland odors.