Placentophagia in naïve adults, new fathers, and new mothers in the biparental dwarf hamster,Phodopus campbelli

Abstract

Placentophagia in mammals typically occurs only in females during the birth. Male hamsters, Phodopus campbelli, with an extensive paternal behavior repertoire eat placenta during the birth and as alloparental juveniles. Two fresh placentae were presented to sexually naïve males and females covering the developmental range from puberty through reproductive maturity and into senescence. Expectant parents and new mothers were also tested. Placentophagia occurred in both sexes at all developmental stages and was higher in reproductive than in naïve hamsters. Placentophagia declined with increasing age in females, but not males. Liver was readily accepted, but acceptance did not decline with age in females, and was not low in juvenile males, confirming that animals distinguished between the two tissues. Senescent females consumed both tissues willingly. In these paternal males, which do not experience pregnancy or parturition, and in naïve females that selectively refuse placenta, the stimuli influencing placentophagia remain unknown.

Paternal Care in Biparental Rodents: Intra- and Inter-individual Variation

“…In virgin male California mice, affiliative behavior toward unrelated pups declines across the juvenile period and remains low into adulthood (Gubernick and Laskin 1994); however, testosterone levels have not been characterized in young males across the pubertal period. In contrast to Mongolian gerbils, prairie voles, and California mice, sexually naïve male Campbell's dwarf hamsters do not show significant changes in affiliative behavior toward pups from the early postpubertal period to mid-adulthood (Gregg and Wynne-Edwards 2005;Vella et al 2005). Again, however, hormonal changes across this period have not been characterized.…”

In uniparental Phodopus sungorus, new mothers, and fathers present during the birth of their offspring, are the only hamsters that readily consume fresh placenta

“…Fresh conspecific liver tissue was included in the experimental design as a control for developmental changes in willingness to consume other meats. Sexually naïve female P. campbelli also have unexpectedly high rates of spontaneous placentophagia (Gregg & Wynne-Edwards, 2005) relative to naïve female rats and mice (Kristal & Graber, 1976;Kristal & Williams, 1973;Kristal, 1980). If this pattern of placentophagia were a general characteristic of the genus Phodopus, then we would expect to find a similar developmental pattern among P. sungorus females.…”

“…Reproductively capable virgin hamsters (30-90 days old) have high rates of placentophagia in both male and female P. campbelli (Gregg & Wynne-Edwards, 2005) and low rates of placentophagia in both male and female P. sungorus (Experiment 1). Thus, P. campbelli placentae were palatable whereas Experiment 1 could not exclude unpalatability as an explanation for the behavior of P. sungorus.…”

“…Except for the species used, all procedures, including animal husbandry, placenta and liver collection, developmental stage assignment, and behavioral testing were identical to those described in Gregg and Wynne-Edwards (2005) and were conducted under protocol 2002-025. Hamsters were drawn from our breeding colony at Queen's University, where they were housed in standard shoebox cages, on wood shavings, at a temperature of 18 AE 1 C and on a 14L:10D photoperiod.…”

“…Work by Kristal and colleagues has suggested that placenta serves as an attractant, encouraging contact between the mother and neonate(s), as well as serving as an opioid enhancing factor (Abbott et al, 1991;DiPirro & Kristal, 2004;Kristal, Thompson, & Grishkat, 1985;Kristal, 1991;Steuer, Thompson, Doerr, Youakim & Kristal, 1987). We recently demonstrated high rates of spontaneous placentophagia in sexually naïve males of the biparental dwarf hamster, Phodopus campbelli, with 100% of male P. campbelli eating placenta the day before they became fathers for the first time (Gregg & Wynne-Edwards, 2005). As such, we suggested that paternal placentophagia in biparental P. campbelli might contribute to paternal behavior in this species.…”