Male-female interactions across the female estrous cycle: a comparison of two species of dwarf hamster (Phodopus campbelli and Phodopus sungorus).

Recent studies in our laboratory have suggested that monogamy may be the preferred mating system in the Djungarian hamster (Phodopus campbelli), whereas the available evidence for the closely related Siberian hamster (P. sungorus) does not show the same pattern. Here we examine the behavior of male-female dyads of both species interacting during 1-hr tests in large, familiar habitats containing defensible nest boxes, food, and water. Levels of aggression within pairs were low, compared with those seen during brief intrasexual encounters, whereas affiliative behaviors, such as sniffs, were high. P. campbelli scent marked more than twice as frequently as P. sungorus. Females of both species scent marked at a constant rate irrespective of their location in the habitat, whereas males scent marked at a higher rate in the female's home area. Two major features of the copulatory pattern differed between the two species: (a) The duration of the ejaculatory lock was five times longer in P. sungorus than in P. campbelli. (b) Both species had approximately the same number of mounts in each ejaculatory series, but the intromission/mount ratio was significantly higher in P. sungorus.