Lunar and temperature effects on activity of free-living desert hamsters (Phodopus roborovskii, Satunin 1903).

Time management of truly wild hamsters was investigated in their natural habitat in Alashan desert, Inner Mongolia, China during summer of 2009, 2010, and 2012. Duration of activity outside their burrows, duration of foraging walks, and nocturnal inside stays were analyzed with the aim to elucidate impact of moon, ambient, and soil temperature. Animal data were determined using radio frequency identification (RFID) technique; for that purpose, individuals were caught in the field and marked with passive transponders. Their burrows were equipped with integrated microchip readers and photosensors for the detection of movements into or out of the burrow. Lunar impact was analyzed based on moon phase (full, waning, new, and waxing moons) and moon disk size. A prolongation of aboveground activity was shown with increasing moon disk size (Spearman ρ = 0.237; p = 0.025) which was caused by earlier onsets (p =-0.161; p = 0.048); additionally, foraging walks took longer (Pearson r = 0.037; p = 0.037). Temperature of different periods of time was analyzed, i.e., mean of whole day, of the activity phase, minimum, and maximum. Moreover, this was done for the current day and the previous 3 days. Overall, increasing ambient and soil temperatures were associated with shortening of activity by earlier offsets of activity and shorter nocturnal stays inside their burrows. Most influential temperatures for activity duration were the maximum ambient temperature, 3 days before (stepwise regression analysis R = 0.499; R² = 0.249; F = 7.281; p = 0.013) and soil temperature during activity phase, 1 day before (R = 0.644; R² = 0.283; F = 7.458; p = 0.004).

Interspecific contact affects phase response and activity in Desert hamsters.

Circadian rhythms enhance survival and reproductive fitness of animals by promoting optimal timing of behavior and physiology with reference to geophysical changes in environment. Although light is considered the dominant stimulus for entraining circadian rhythms, social stimuli can also act as zeitgebers. The aim of this study was to analyze how Desert hamsters (Phodopus roborovskii) coordinate their behavior in time with that of animals of another competing species (Mongolian gerbils, Meriones unguiculatus). First, the behavior of hamsters was analyzed during a step-wise avoidance test. Two effects were observed: a) spatial separation if it was possible or b) shortening of the activity period due to contact without chance for avoidance. The latter finding was now further analyzed using a phase response curve (PRC). Here, phase shifts of Desert hamsters caused by single social interactions with Mongolian gerbils were quantified. Phase advances during the rest period were found at CT3 and CT9, a similar tendency was observed at CT6. A second phase advance was determined at CT18, coinciding with the end of the activity period. Then, it was tested whether additional activity during the stimulus was a trigger for the phase response. Although an increase in activity occurred especially when stimuli were applied during the rest period, there was no general relation between additional activity measured and the phase response shown. Overall, relevance of interspecific contact as nonphotic zeitgeber was indicated by phase shifts in a phase response curve. The shape of it can be explained by two behavioral adaptations; stress and contact avoidance.

Male expulsion in cooperative Mongolian gerbils (Meriones unguiculatus).

Mongolian gerbils are territorial rodents of steppes and semideserts of Mongolia and Northern China. At least under laboratory conditions, the family life is characterized by long-term harmonious and short-term aggressive periods in which some members are expelled. The purpose of this study was to clarify which features of male offspring promote their expulsion. Therefore body mass, absolute and relative weight of testes and epididymis, histology of testes and testosterone concentrations were analyzed in males derived from five families living in semi-natural enclosures with food and water ad libitum. Males expelled (EFM, n=40) had significantly higher relative testes and relative epididymis weight and higher testosterone concentrations in harmonious periods than it did non-attacked ones (IFM, n=13). A stepwise discriminant analysis has established the relative testes weight as decisive for the affiliation to EFM or IFM. Based on this parameter, 71.7% of the offspring could be classified correctly. Moreover, histological results showed that 50.0% of integrated and 29.4% of the expelled family members had incomplete spermiogenesis, indicating a reduced fertility. It is concluded, that males do compete for reproduction within the families which triggers the expulsion of the males with the highest reproductive capacity.

Social categories in families of Mongolian gerbils.

Mongolian gerbils are a species of rodent in Asia living in families, although aggression occurs within these social units. The aim of this study was to determine the causes for the surge of intrafamily aggression and to characterize different types of animals. Due to behavioral measures, animals were assigned to distinct social categories and the consequences of social stress were analyzed on an individual level. Four families established from founder pairs were kept for up to 2.5 years in large enclosures. Social interactions within each family were recorded for at least 5 days per week throughout the long-term experiment and fecal samples were collected weekly for the determination of corticosterone concentration. Moreover, adrenals were weighed and histologically analyzed. Two main causes for the outbreak of aggression were distinguished: changes in family structure and female competition for reproduction. As a result of these aggression periods, it was possible to divide animals into social categories: (1) integrated family members (IFM), (2) founder pair animals (FPA) and (3) expelled family members (EFM). Integrated animals had the lightest adrenal glands [related to the fat-free mass (FFM)] and lowest corticosterone level in aggression periods. Founder animals were never attacked by other members, reproduced successfully and displayed the highest stress level in most of the measured parameters. EFM were attacked and excluded mainly by the founder females. Their stress level was intermediate.