Paternal behavior in the spiny mouse (Acomys cahirinus)

The responsiveness of adult male spiny mice (Acomys cahirinus) to both their own and alien precocial young was investigated. Paternal behavior was manifested primarily by the males huddling with their offspring and the coordination of pup attendance between adult males and females. With less than 2 days exposure to their own neonates, males were found to discriminate between their own and alien young. Experience plays an important role in the development of paternal behavior in spiny mice. Males who have never had pups of their own sniff and attack unfamiliar neonates more than males who have fathered pups. The adaptive significance of paternal investment in this uniquely precocial murid rodent was discussed.     

Maternal discrimination and the development of sex differences in exploratory behaviour in infant spiny mice (Acomys cahirinus)

The present paper reports sex differences in exploratory behaviour by infant Spiny Mice, Acomys cahirinus, that may, in part, be related to differences in maternal behaviour towards pups; like some other rodents, mother Acomys differentiate behaviourally between male and female pups. In Experiment 1 infant Acomys were allowed to explore a novel arena. This experiment showed that even by Day 3 (the day of birth=Day 1) female Acomys explored a novel environment more than males; they entered the arena sooner than males and spent more time in contact with a novel object. Experiment 2 showed that infant females were more active than males when observed in the home cage in the presence of their parents and made more approaches to the mother. Mothers, on the other hand, directed more licking behaviour towards males. Experiment 3 focused on the exploratory behaviour of individual pups in the presence of the mother. Given access to a large, complex arena, female pups explored more than males. The results also showed that mothers direct more of their social interactions towards sons than daughters, particularly when pups are about a week old. Some mothers appear to “direct” the movement of their offspring, by blocking their forward movement; this was done more often to male than to female pups. The data suggest that the previously observed changes in exploratory behaviour at this time, and the emergence of sex differences in exploration, may in part depend upon the mothers' reactions to pups by sex.     

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.     

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.     

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.     

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.     

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.     

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.     

Social preference of female gerbils (Meriones unguiculatus) as influenced by coat color of males

Female gerbils (Meriones unguiculatus) of three distinct coat colors (agouti, black, and sandy or pink-eyed dilution) were tested in a Y-maze whose arms led to compartments containing unfamiliar male gerbils of varying coat colors. The stimulus animals were separated from the females by a Plexiglas door. The trials lasted for 2 min and each female was exposed to the following four combinations: two males of the same coloring as the female; one male of the same color and another of a different color from the female; both males of different color from the female. The number of crossings to the left and right arms was relayed by photocells to an IBM PC computer. The results indicate that agouti females preferred visiting the arm occupied by agouti males while those of the other coat colors showed no preference for the "wild-type" males. Instead, sandy and black female gerbils preferred to be in proximity with those of non-wild types.     

Development and expression of autogrooming in the Mongolian gerbil, Meriones unguiculatus

Adult gerbils, Meriones unguiculatus, autogroom their body parts in the order: mouth--nose, face, ears, flank, ventrum, and tail. This is the identical order in which the autogroom matures during the first 33 days of life. The parallel sequencing increases our understanding of neurophysiological processes underlying movement patterns and also indicates how movement patterns evolve.