Effects of blindness on play fighting in golden hamster infants.

The effects of bilateral optic enucleation on play fighting in golden hamster infants were studied. The behaviors of blind-blind (BB), blind-intact (BI) and intact-intact (II) dyads were recorded from the 30th to the 36th day of age. It has been noted that the differences in physical contact, play fighting and grooming time, as well as in the percentage of time spent in play fighting, the amount of locomotion and other activities of BB, BI and II were small and statistically insignificant. The mean number of active and passive pinning in all groups was equivalent and the alternation of active and passive pinning, or vice versa, was around 50%, showing that posture during play fighting is not an indicator of dominance. It has been concluded that vision is not important for either the initiation or the modulation of play fighting in golden hamsters.

Sex differences in the play fighting activity of golden hamster infants.

Play fighting of homosexual and heterosexual dyads in golden hamsters was studied. The behaviors of male-male (MM), female-female (FF), and female-male (FM) dyads were recorded from the 25th to the 31st day of age. Play fighting activity of heterosexual dyads was depressed since MF and FM dyads exhibited a significantly high physical contact time and engaged in less play fighting, with a significantly lower time spent on such activity. Alternation ratio in the pinning posture was very high and subjects did not differ in the mean number of active (top) and passive pinning (under) in each dyad, showing an inexistence of sex dominance. In most cases, differences in the performances of MM and FF dyads were not significant. We have concluded that play fighting in golden hamsters may be predominantly modulated by environmental stimuli (sex of the partner) rather than by endogenous stimuli (androgen level).

Play fighting of juvenile golden hamsters (Mesocricetus auratus): effects of two types of social deprivation and days of testing.

The effects of social deprivation schedules and days of testing on the play-fighting of juvenile golden hamsters were investigated. In Experiment 1, subjects totally (individually housed) or partially isolated (individually housed, but separated by a wire mesh 2 cm from another animal) for a period of 48 h spent significantly increased peer-peer bodily contact, play fighting, and play-fighting relative time (% of bodily contact time spent in play fighting), but exhibited decreased locomotor activity on the 1st day of testing. In Experiment 2, subjects reared since the 10th postnatal day with their mothers alone (chronically deprived of peer-peer social interactions) exhibited similar performances, except that locomotor activity was not affected. All dyads exhibited increased pinning turbulence (number of pinnings divided by time spent in play fighting) on the 1st day of testing, and the interactions between variables (deprivation schedules and days of testing) were statistically significant in most cases, suggesting that unfamiliarity between interactors also affect the performances of animals. We conclude that golden hamsters are sensitive to social deprivation, mothers do not substitute peer companions, animals reared in single-infant litters basically behave like socially-isolated animals, and the effects of induced social deprivation are reversible and disappear on days following testing.

Cross-fostering between two species of marmosets (Callithrix jacchus) and Callithrix penicillata).

Cross-fostering technique can be defined as adoption of infants by adults of other species. This phenomenon is poorly investigated because very young animals have few opportunities to interact peacefully with non-conspecific adults, either in captivity or in natural conditions. This study describes the induction of cross-fostering in captivity between white tufted-ear (Callithrix jacchus) and black tufted-ear marmosets (Callithrix penicillata). We conclude that this technique can be very useful for preserving the life of rejected by parents or orphan infants, mainly in the case of species with low reproduction rate in captivity or those threatened by extinction, as well for investigating the environmental effects on the typical behavior of species (courtship, food preference, vocalization patterns, e.g.).

Effects of litter size on maternal care, body weight and infant development in golden hamsters (Mesocricetus auratus).

The effects of litter size on maternal care, body weight and infant development of golden hamsters were investigated from a longitudinal perspective. Litters were culled to 1,3,6 and 9 pups, and the behavior and body weight of mothers and pups were recorded from the 5th to the 25th postpartum day. We noted that the time spent by mothers in bodily interactions with pups decreased as a function of litter size; maternal pup retrievals reached their maximum around the 13-15th day, which coincided with the increased locomotor activity of pups at this time; the total number of pup retrievals by the mother increased as a function of the litter size, but mothers of larger litters were more 'efficient' (i.e. they failed less frequently in exhibiting a full sequence of retrievals) and exhibited a low litter-size proportional mean number of retrievals. All mothers gradually lost body mass throughout lactation, and decrease in body weight was significantly related to litter size. The mean body weight gain (%) by pups decreased as a function of litter size, but we also noted that single and larger litter pups exhibited a decreased body mass (grams) by the 15th day, suggesting that infant development may be impaired at both extremes of experimental conditions. We concluded that the behavior of mothers and pups was affected by the litter size, and it appeared that the litter had an optimal size-not so large as to overlap the mother's physical capacity, and not so small as to fail to compensate for the parental investment.

Hand preference during behavioral tests and spontaneous activity in two species of common marmoset (Callithrix jacchus and Callithrix penicillata).

Hand preference in two adult C. jacchus (one male and one female) and five C. penicillata (three adult females and two 70-day-old male and female infants) was examined in this study. Animals were housed in large wire mesh cages and daily tested twice during 40 consecutive days in 15-minute experimental sessions. Tests were carried out with dog food pellets and were as follows: 1) food taking from a glass cylinder (12 cm long x 5 cm diameter), 2) food taking from an opaque plastic flask (11 cm long x 9.5 cm diameter) behind wire mesh, 3) food taking under the cage floor and 4) spontaneous activity (food manipulation, self-grooming and scratching behavior, and grasping wire mesh). It was observed that 1) subjects exhibit a high manual ability in all testing conditions, 2) hand biases occurred, but the subjects either reversed hand preference or the preference was ambiguous as the performances are examined in a longitudinal perspective, 3) hand biases were clearly more visible in test 1, which may be due to the complexity of this task itself, 4) hand biases were not similar in all testing conditions--i.e., subjects were left--in one test and right-handed in another-, and 5) the main results were very similar in both C. jacchus and C. penicillata and seem to be not dependent on either sex or age.

Cross-fostering between two species of marmosets (Callithrix jacchus) and Callithrix penicillata)

Cross-fostering technique can be defined as adoption of infants by adults of other species. This phenomenon is poorly investigated because very young animals have few opportunities to interact peacefully with non-conspecific adults, either in captivity or in natural conditions. This study describes the induction of cross-fostering in captivity between white tufted-ear (Callithrix jacchus) and black tufted-ear marmosets (Callithrix penicillata). We conclude that this technique can be very useful for preserving the life of rejected by parents or orphan infants, mainly in the case of species with low reproduction rate in captivity or those threatened by extinction, as well for investigating the environmental effects on the typical behavior of species (courtship, food preference, vocalization patterns, e.g.).