Directional responses to sounds in young gerbils (Meriones unguiculatus)

Three experiments were conducted to determine the ability of infant gerbils to approach an auditory stimulus. In the first experiment, gerbil pups, 16-23 days of age, were tested in a circular apparatus with a central start area and a movable sound source located at one of eight positions around the perimeter. Stimuli included high- and low-intensity presentations of a tape-recorded gerbil social call, a broad-band white noise stimulus, and a no-stimulus control condition. The subjects showed a strong tendency to approach the low-intensity social call and a less pronounced tendency to approach the white noise. In the second experiment, gerbil pups were tested in the same apparatus with or without ear blocks to determine the role of binaural cues in directional approach responding. The tendency to approach a low-intensity vocalization was disrupted by obstruction of one ear but not by blocking both ears. Thus, binaural balance was shown to be important for early sound localization. In the third experiment, the tendency to approach a social call was compared at different ages, 12-15, 16-19, 20-23, and 24-27 days after birth. Approach responses were first seen at 16-19 days. The responses continued during the 20-23-day period but began to wane at 24-27 days of age.     

Within-session changes in operant responding when gerbils (Meriones unguiculatus) serve as subjects

Recent research has demonstrated that rate of responding frequently changes in a robust and systematic manner during experimental sessions in which organisms engage in operant responding. One potential cause for these changes in response rate is that levels of exploration change during experimental sessions and that high levels of exploration interfere with operant responding. Several studies have shown that gerbils (Meriones unguiculatus) explore at a constant rate during experimental sessions. The present study examined the response pattern produced by gerbils responding for food delivered by several simple schedules of reinforcement. Results indicated that robust changes (between 200 and 400%) in response rate occurred during the experimental sessions. These data argue against a role for exploration in the production of within-session changes in operant response rate.     

Flavour neophobia in gerbils (Meriones unguiculatus) and hamsters (Mesocricetus auratus)

Flavour neophobia in gerbils and hamsters was studied by comparing the ingestive/pouching behaviour of these animals when presented with either a familiar unflavoured peanut or a novel one that imparted basic flavours such as sweet, salty, sour, or bitter. Neophobia was expressed by an aversion towards the novel nut manifested by greater latency either to ingest it (gerbils) or to deposit it in the cheek pouch (hamsters) relative to that of the unflavoured one. This method, involving reactions to the taste of novel solid food, provides a more sensitive measure than the traditional one measuring intake of a novel flavoured fluid. The results indicated that gerbils and hamsters encountering either a sweet, salty, or sour nut for the first time showed a neophobic reaction. However, there was no apparent sign of neophobia when the animals were tested with a nut flavoured with quinine. The theoretical implications of these findings are discussed.     

A testosterone-mediated trade-off between parental and sexual effort in male mongolian gerbils (Meriones unguiculatus)

Effects of testosterone (T) on parental behavior of male Mongolian gerbils (Meriones unguiculatus) were examined. After undergoing gonadectomy, castrated males were implanted with empty capsules or capsules containing T; sham-operated males were implanted with empty Silastic capsules. Subsequently, each male was paired with a pregnant female, and after delivery, families were observed 15 min/day for 20 days. Gonadectomized males without T spent more time in contact with, huddling over, and licking pups than did either sham-operated males or gonadectomized males with T. When given a choice between nest sites and displaced pups, females and males with low T preferred pups, whereas intact males and castrated males with T preferred nest sites. The findings are consistent with E. D. Ketterson and V. Nolan's (1994) hypothesis implicating T in mediating trade-offs between parental and sexual effort.     

Depth perception in Mongolian gerbils (Meriones unguiculatus) and spiny mice (Acomys russatus and A. cahirinus)

Depth perception in gerbils and spiny mice was studied with a modified visual cliff which varied the height of a platform from 5.08 cm to 25.4 cm and presented animals with an apparent drop-off to a patterned or a white field. Time to descend from the platform and orienting response frequency were recorded. For gerbils neither measure varied significantly between the platforms. Both Acomys species increased descent time and orienting response frequency as platform height increased. The results suggest that both gerbils and spiny mice can perceive depth, though there appears to be a difference between the species' use of sensory cues in descending from a visual cliff. The spiny mice appear to rely more on visual cues than do the gerbils. The data also reveal subtle behavioral differences between the Acomys species that may relate to their successful sympatry. The results are discussed by alluding to ecological differences between these species in their natural habitats.     

Dietary pyridoxine loadings affect incidence of "spontaneous" seizures among magnesium-deprived Mongolian gerbils (Meriones unguiculatus)

The "spontaneous" tetanic attacks in magnesium (Mg) deficiency resemble those occurring in pyridoxine (Pyr) deficiency. A common mechanism may underlie both seizure patterns. Nine groups (n = 10) of male Mongolian gerbils that were Mg-deprived, Pyr-deprived, or both were used to explore this possibility. The animals were tested for spontaneous seizing in an open field at four-day intervals over 40 days. By the end of the period, 70% of the gerbils that were both Mg- and Pyr-deprived had seized, and 90% had died. One fatality, but no seizures, occurred among Pyr-deprived groups given 500 to 2,000 ppm Mg in the food. No seizures occurred among the Mg-deprived groups fed 20 to 100 ppm Pyr, though several animals given 20 ppm Pyr died. Deaths and seizures occurred within Mg-deprived groups fed more than 100 ppm Pyr. A possible role of Pyr in Mg metabolism is discussed.     

Mate recognition by urine odors in the Mongolian gerbil (Meriones unguiculatus)

We examined the responses of male and female gerbils housed in opposite- or same-sex pairs to the urine odors from their cage-mate and those of an unfamiliar gerbil of the same sex. Gerbils housed in mated pairs spent more time investigating the odor of their partner. They also emitted more modulated ultrasonic vocalizations in the presence of their partner's odor than in the presence of the unfamiliar odor. Gerbils housed in same-sex pairs did not respond differentially to the odor of their cage-mate. There were sex differences in the frequency of ventral scent-marking and modulated vocalizations, with males showing more of these behaviors than females. The urine odor of the gerbil's mate can thus be discriminated from those of other gerbils. Recognition of individual odors may promote affiliative behavior and reduce aggression, thus playing an important role in pair maintenance in gerbils.     

Effects of olfactory bulb ablation and androgen on marking and agonistic behavior in male Mongolian gerbils (Meriones unguiculatus).

Male Mongolian gerbils, selected for high marking frequency, were paired with male opponents, and marking and fighting behavior were recorded. Animals then underwent castration, bilateral bulbectomy, unilateral bulbectomy, the combined operations, or a sham operation; and their behavior was again observed. All operated animals showed drastic reduction in both marking and aggressive encounters. Injections of testosterone propionate (TP) produced complete restoration of marking in castrates, but not in bilaterally or unilaterally bulbectomized animals or combined operates. The exhibition of aggression after injections of TP, however, was enhanced to supernormal levels in bulbectomized or bulbectomized-castrated animals. The results suggest the following: that removal of the olfactory bulbs may eliminate a critical neural input necessary for the normal expression of marking and agonistic; that although marking and fighting are influences by olfactory input and gonadal steroids, their regulatory mechanisms may not be identical; and that removal of the bulbs may sensitize a neural mechanism controlling aggression, thus potentiating its elicitation following administration of exogenous androgen.     

The best men are (not always) already taken: female preference for single versus attached males depends on conception risk

Because men of higher genetic quality tend to be poorer partners and parents than men of lower genetic quality, women may profit from securing a stable investment from the latter, while obtaining good genes via extrapair mating with the former. Only if conception occurs, however, do the evolutionary benefits of such a strategy overcome its costs. Accordingly, we predicted that (a) partnered women should prefer attached men, because such men are more likely than single men to have pair-bonding qualities, and hence to be good replacement partners, and (b) this inclination should reverse when fertility rises, because attached men are less available for impromptu sex than single men. In this study, 208 women rated the attractiveness of men described as single or attached. As predicted, partnered women favored attached men at the low-fertility phases of the menstrual cycle, but preferred single men (if masculine, i.e., advertising good genetic quality) when conception risk was high.