High maternal aggression in dwarf hamsters (Phodopus campbelli andP. sungorus)

Abstract

:::::::::::::::: :::::::::::::::: : The defense of offspring, termed maternal aggression, is a highly conserved behavior in mammals, including rodents. This study examined relative levels of maternal aggression in two closely related dwarf hamster species, Phodopus campbelli and P. sungorus, that normally inhabit high latitude, boreal environments. When tested with first litters and with the breeder male remaining with the female (for P. campbelli the male is necessary for successful rearing of offspring), both species exhibited high levels of maternal aggression with average duration of aggressive behavior480 sec for a 10 min test. For P. sungorus, males are not required to rear offspring. P. sungorus females with either one or multiple litters (singly housed after impregnation) exhibited significantly higher levels of aggression (4300 sec) relative to females co-housed with the sires. In terms of species differences in attack style, P. campbelli exhibited a boxing or clawing strategy for B50% of total attack time, but for P. sungorus, this form of attack occurredo5% of the time. For P. sungorus, attacks to the vulnerable belly and flank constituted490% of all attacks, but these regions were attacked B50% of the time for P. campbelli. A survey of levels of maternal aggression of rodents in other genera suggests that maternal aggression in Phodopus is at the high end of the spectrum. Results of this study suggest that the presence of the breeder male may actually suppress aggression in P. sungorus. This fact, as well as its high level of aggression and its distant relationship to mice and rats, suggest P. sungorus as a possible model for future studies on the neurobiological basis of maternal aggression. The relationship between the high rates of maternal aggression and life history strategy in Phodopus is discussed. Aggr. Behav. 31:294–302, 2005. r 2005 Wiley-Liss, Inc.