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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phodopus campbelli detect reduced photoperiod during development but, unlike Phodopus sungorus, retain functional reproductive physiology

Golden (Mesocricetus auratus) and Siberian (Phodopus sungorus) hamsters are widely used as animal models for seasonal reproduction; but M. auratus shows no developmental delay in short days until after sexual maturity, whereas P. sungorus juveniles delay development in short days. As the photoperiodic response of Phodopus campbelli is not well established, litters of the two Phodopus species were gestated and reared under long days (14 h light:10 h darkness) or short days (10 h light:14 h darkness) until 70 days of age. As expected, under short photoperiod P. sungorus showed reduced body, testes, epididymides, uterus, and ovary weight; antral follicles and corpora lutea were absent and vaginae remained closed. Animals moulted to winter pelage, and low concentrations of each of leptin, testosterone, and prolactin were present in male serum. Phodopus campbelli juveniles also responded to the short photoperiod as measured by reduced body, testes, epididymides, and ovary weight. The summer pelage persisted. However, both sexes of P. campbelli developed functional reproduction under 10 h light:14 h darkness. All females had a patent vagina by 10 weeks; ovaries contained antral follicles and corpora lutea, and uteri were not reduced in weight. In males, the concentrations of testosterone, leptin, and prolactin were not reduced by short photoperiod. Developmental patterns in the three species of hamster, therefore, differ and are not predicted by relatedness or latitude of origin. Other ecological traits, such as predictability of summer rainfall, ambient temperature, and differential responses to social cues might be important.     

Differences in behavioral responses to a competitive mating situation in two species of dwarf hamster (Phodopus campbelli and P. sungorus).

Social groups consisting of a female and two adult males, of two closely related species, Phodopus campbelli and P. sungorus, were observed during a 2-hr mating test. The behavioral analysis revealed (a) significant differences between the two species in the ability of the dominant male to exclude the subordinate male from mating with the estrous female and (b) significant changes in the pattern of copulation by the dominant male in response to the presence of a second male even when the second male was not mating with the female. Dominant male P. sungorus were always successful in preventing subordinate males from mating. In contrast, subordinate male P. campbelli mated with the female in 6 of 12 groups in spite of high levels of aggression and the potential for serious injury. When both P. campbelli males mated, dominant males ejaculated first and most frequently. The response to the presence of a second male in P. sungorus included an accelerated copulatory pattern, with decreased durations of individual ejaculatory series and postejaculatory refractory periods. This resulted in an average of one extra ejaculation during the first hour of testing. The temporal pattern of mating in P. campbelli was not accelerated by the presence of a second male, but the intromission/mount ratio was increased significantly, and the duration of the ejaculatory lock decreased. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Repeated exposure to stress across the childhood-adolescent period alters rats' anxiety- and depression-like behaviors in adulthood: The importance of stressor type and gender.

This research tests the hypothesis that specific forms of adversity in early life map onto behavioral signs analogous to depression versus anxiety in later life. Male and female rats were exposed to either severe sporadic stress or chronic mild stress during the childhood-adolescent period, and their behavior was tested in adulthood. Males in the severe sporadic stress group showed exaggerated anxiety-related behaviors, as indicated by increases in shock-probe burying and escape-like responses (jumps) from the open arms of the elevated plus-maze. Females exposed to severe sporadic stress displayed no change in burying behavior but did display increases in escape behavior. These same females also exhibited behaviors analogous to depression that manifested as decreased sucrose consumption. The chronic mild stress regime produced effects only in females, including reduced burying, decreased sucrose consumption, and an exaggerated corticosterone response to cold-water immersion stress. Findings reiterate the importance of early life experience to the development of adult psychopathologies and emphasize the need to consider both the type of early experience and gender differences in these analyses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Novel patterns of progesterone and prolactin in plasma during the estrous cycle in the Djungarian hamster (Phodopus campbelli) as determined by repeated sampling of individual females

In contrast to results from previous research, a surge of progesterone (P4) on the afternoon of proestrus was consistently detected in Djungarian hamster females. However, the timing of maximal P4 levels varied from 1200 to 1900 h across females; this impeded detection of the surge in earlier studies. No role for P4 in the induction of behavioral receptivity was found. Behavioral receptivity was induced in ovariectomized females with physiological levels of estradiol typical of an estrous cycle (60-180 pg/ml). P4 did, however, terminate receptive behavior within 48 h. Prolactin (PRL) was present as surge levels on each day of the cycle except diestrus 1, during which PRL remained at basal levels in all females. This pattern distinguishes the Djungarian hamster from the rat and mouse, which have PRL surges only on the afternoon of proestrus, and the golden hamster, which has a PRL surge on each of the 4 days of the estrous cycle. Diestrus 1, with P4 high and PRL low, was clearly distinct from Day 2 of Djungarian hamster pregnancy, during which P4 is low and PRL is surging. Therefore, postcoital P4 levels change within 34 h and before rescue of the corpus luteum. As Day 2 of pregnancy is also the most sensitive time for a mate-removal pregnancy-blocking response in P. campbelli, this hormonal profile may be associated with sensitivity to those stimuli.