A study of postnatal appendicular skeletal maturation in captive-born squirrel monkeys (Saimiri boliviensis)

This study is based on a mixed longitudinal radiographic sampling of appendicular bones in 82 captive-born squirrel monkeys (Saimiri boliviensis). All appendicular ossification centers had appeared radiographically by 17 weeks of age, and epiphyseal fusion was complete by 47-53 months of age. No statistically significant differences were found between the sexes in comparisons carried out at birth and at 6 and 8 months of age. Valid sex comparisons could not be made at other ages owing to the small size of the sample. The sequence of appearance of the ossification centers (Spearman correlation coefficient of Saimiri vs. Callithrix = 0.68) shows greater interspecies differences than the sequence of fusion (Saimiri vs. Callithrix = 0.88).     

Maternal recognition of individual infant squirrel monkeys from isolation call playbacks

Responses of six squirrel monkey (Saimiri sciureus) mothers to playback of a single call type, the “isolation peep,” made by their own infants were tested after mothers and infants had been separated for more than a week. The playback tapes were edited from tapes containing mixed vocal material recorded when infants and mothers could see but not touch each other. Mothers showed recognition of their own infants compared to other familiar infants by increases in four measures of proximity to the speaker. These data provide evidence that maternal recognition of infants by means of acoustic cues is possible when the test stimuli consist of examples of a single call type with demonstrated individuality.     

Effect of separation distance on isolation call structure in squirrel monkeys (Saimiri sciureus)

Isolation calls of captive squirrel monkeys were recorded by separating infants from their natal group members and then permitting vocal contact between the “lost” baby and the group at systematically varied distances. Separated infants gave longer calls at greater separation distances from their natal group members, and responding adults and juveniles similarly extended the length of their vocalizations. In the longer variants, a highfrequency element was prolonged, which is considered to be an example of the net advantage of a “frequency window” in the ambient noise of environments.     

Abnormal behaviors in nursery-reared squirrel monkeys (Saimiri sciureus)

Seventeen squirrel monkeys (Saimiri sciureus), 11 nursery-reared and six mother-reared, were monitored to clarify the type and degree of deviant behaviors that result from rearing this species in the nursery. Two observation periods were used: the first when the subjects averaged 6.7 months of age, the second when they averaged 15.5 months. Thirteen activities involving variations of nonnutritive orality, stereotypic posturing, and agitated behaviors were seen in the nursery-reared subjects, but never in the mother-reared subjects. No consistent gender, subspecies, or age differences were evident. Squirrel monkeys, like chimpanzees and some Old World monkeys, do develop atypical self-directed behaviors when deprived of normal stimulation during early development.     

Taxonomy of squirrel monkeys genus Saimiri (Cebidae,platyrrhini): A preliminary report with description of a hitherto unnamed form

Two groups of squirrel monkeys, genus Saimiri, are distinguished by external characters. The first, or Roman type, contains Saimiri boliviensis of upper Amazonia south of the Rio Marañón-Amazonas, with two subspecies of which S. boliviensis peruviensis is described as new. The second group, or Gothic type, contains three species: Saimiri sciureus with four subspecies distributed over much of tropical South America, Saimiri ustus of Brazil between the south bank Amazonian Rios Purús and Xingu, and S. oerstedi isolated on a Pacific coastal area straddling Costa Rica and Panamá. The geographic range of S. sciureus overlaps parts of those of S. ustus and S. boliviensis. Incomplete karyotypic data indicate that the diploid number of chromosomes for the genus is 44. Geographic variation is characterized by reduction from seven to six or five paired acrocentric autosomes through pericentric inversion with reciprocal increase in number of paired submetacentric or subtelocentric autosomes. Geographic distribution, behavior, sexual dimorphism including dichromatism, and hybridization are discussed. Ventral guide hairs for orientation of subprecocial newborn toward the maternal mammae are described. Distinguishing characters of species and subspecies are provided in a key. The taxons are listed with the taxonomy of each discussed, their geographic distribution plotted and mapped.     

Taxonomy of squirrel monkeys genus Saimiri (cebidae,platyrrhini): A preliminary report with description of a hitherto unnamed form

Two groups of squirrel monkeys, genus Saimiri, are distinguished by external characters. The first, or Roman type, contains Saimiri boliviensis of upper Amazonia south of the Rio Marañón-Amazonas, with two subspecies of which S. boliviensis peruviensis is described as new. The second group, or Gothic type, contains three species: Saimiri sciureus with four subspecies distributed over much of tropical South America, Saimiri ustus of Brazil between the south bank Amazonian Rios Purús and Xingu, and S. oerstedi isolated on a Pacific coastal area straddling Costa Rica and Panamá. The geographic range of S. sciureus overlaps parts of those of S. ustus and S. boliviensis. Incomplete karyotypic data indicate that the diploid number of chromosomes for the genus is 44. Geographic variation is characterized by reduction from seven to six or five paired acrocentric autosomes through pericentric inversion with reciprocal increase in number of paired submetacentric or subtelocentric autosomes. Geographic distribution, behavior, sexual dimorphism including dichromatism, and hybridization are discussed. Ventral guide hairs for orientation of subprecocial newborn toward the maternal mammae are described. Distinguishing characters of species and subspecies are provided in a key. The taxons are listed with the taxonomy of each discussed, their geographic distribution plotted and mapped.     

Species differences in adrenocortical activity of new world primates: Response to dexamethasone suppression

The effect of dexamethasone-induced alteration of adrenocortical activity was assessed in two species of New World primates: Saimiri sciureus and Callicebus moloch. Basal and stress levels of corticosteroids were determined following treatment with three doses of dexamethasone (0, 50, or 500 μg/kg). Saimiri showed substantially higher basal levels of corticosteroids than did Callicebus and a greater incremental corticosteroid response to physical restraint. Dexamethasone was found to reduce basal corticosteroids in both species, although this effect was greater for Callicebus than for Saimiri Moreover, the adrenocortical response to physical restraint was reduced by dexamethasone treatment in Callicebus but not in Saimiri. The pattern of results suggests that the species differ in the mechanisms mediating adrenocortical activity.     

Diurnal variations of androgens in sexually mature male Bolivian squirrel monkeys (Saimiri sciureus) during the breeding season

To assess diurnal fluctuations of serum androgens and cortisol in adult male Bolivian squirrel monkeys, these steroids were measured at predetermined times (0300, 0900, and 2300 hours) during two separate 24-hour periods in the breeding season (January 1983 and late November 1983). A significant diurnal change in serum cortisol was noted, with a nadir of 99.9 ± 11.9 μg/dl (x? ± SEM) at 2300 hours and a peak of 168.9 ± 7.8 μg/dl at 0900 hours. Conversely, a nadir in serum testosterone was noted at 0900 hours (117 ± 26.5 ng/ml) increasing to a peak of 328.5 ± 57.9 ng/ml at 0300 hours. Serum androstenedione and dehydroepiandrosterone followed a pattern similar to testosterone, with a serum androstenedione (176.4 ± 34.9 ng/ml) and dehydroepiandrosterone (11.7 + 1.8 ng/ml) nadir at 0900 hours and a plasma androstenedione (494.5 ± 55.4 ng/ml) and dehydroepiandrosterone (32.5 ± 4.1 ng/ml) peak at 0300 hours. Parallel changes of testosterone, androstenedione, and dehydroepiandrosterone suggest a significant contribution of all three androgens from a common site, the testes. In contrast to old world primates and humans, serum androstenedione levels exceeded serum testosterone levels in this species.     

Use of foraging racks and shavings as enrichment tools for groups of rhesus monkeys (Macaca mulatta)

Searching for and processing food are important activities of free-ranging primates. In contrast, captive primates spend little time foraging. Their food is readily available, easily obtained, and can be consumed quickly. The present study compared the use of foraging racks and a shavings substrate as two manipulations used to alter feeding behavior in nonhuman primates. Each method was tested in between two baseline periods (no racks or shavings present). Behavioral data were collected using a 30-sec scan sampling procedure for 1 hr during the feeding period. Both the rack conditions and the shavings condition decreased passive feeding behavior in the subjects. The use of racks also resulted in increased cage usage, activity, and movement, and decreased social proximity; the use of shavings resulted in decreased agonism. This study suggests that foraging racks and shavings are useful devices for environmental enrichment. © 1995 Wiley-Liss, Inc.     

Age-related hormonal differences in cycling squirrel monkeys (Saimiri boliviensis boliviensis)

This study was planned to evaluate the poor reproductive performance of aged squirrel monkeys in a self-sustaining breeding colony. Two groups of monkeys aged 6–8 years (Group 1), and >12 years (Group 2) were evaluated. During the midbreeding season, daily blood samples were obtained for a period of 35 days from 10 animals in each group. Blood samples were assayed for serum estradiol (E), progesterone (P), and bioassayable luteinizing hormone (bio-LH) concentrations and the data were analyzed by ANOVA (analysis of variance). Bio-LH surges were less frequent in the aged breeders (Group 2). Total P output during periovulatory period (day ?;3 to day + 3) and the total P output during the luteal phases of the estrus cycles were significantly lower in aged squirrel monkeys (Group 2, P < 0.003). Although E peaks occurred less frequently in Group 2, they had higher concentrations as compared to Group 1 (P < 0.003). Cumulative periovulatory and luteal phase E levels did not differ between the two groups. The reduction in P output in aged squirrel monkeys may interfere with proper implantation, thus contributing to the lower pregnancy rate observed in this age group. The decreased frequency of bio-LH surges indicated less frequent ovulations in the aged animals which may further impair reproduction with aging. © 1994 Wiley-Liss, Inc.     

Responsiveness and Somatotopic Organization of Anterior Parietal Field 3b and Adjoining Cortex in Newborn and Infant Monkeys

Microelectrodes were used to record from somatosensory areas 3b and adjoining areas 3a and 1 in newborn monkeys. At birth, area 3b was responsive to cutaneous stimuli and had an adult-like somatotopic organization in marmosets and one squirrel monkey, while areas 1 and 3a had only limited responsiveness. In newborn macaque monkeys, cortex was unresponsive to cutaneous stimuli; however, by 1 month, areas 3b and 1 appeared to be adult-like in responsiveness and somatotopic organization.     

Birth Seasonality in Alouatta caraya in Northern Argentina

Given appropriate ecological and social conditions, natural selection should favor individuals that can concentrate their reproductive events to a particular time of the year that offers high opportunities for infant survivorship. Previous studies on births in Alouatta caraya in Northern Argentina revealed the existence of a peak during the dry season—a period with scarcity of food resources—in mainland gallery forest (G. E. Zunino, Extra 133: 1–10, 1996). The time of conception and the period of independence of the offspring are positively correlated with precipitation, temperature and availability of food. Offspring became independent from their mothers when the availability of resources was high, and conception coincided with the peak of fruit production. Our goal was to examine patterns of birth seasonality in Alouatta caraya in flooded forest on an island in Northern Argentina for comparison with the mainland population. Both sites are at similar latitudes, but differ in forest type. The results indicate that the availability of new and mature leaves is more consistent throughout the year in the flooded forest (p<0.05); however, there was no difference in the availability of fleshy fruits between sites (p>0.05). The pattern of births differed between the gallery forest and the flooded forest (2-way Anova, p<0.001). In the flooded forest births occurred throughout the year, which supports the contentions that howlers do not have a fixed birth season and that the observed variation in the timing of births appears to represent a facultative behavioral response to changes in food availability.     

Susceptibility of squirrel monkey (Saimiri sciureus) to infection by mammalian schistosomes.

In a study of host-schistosome relationships, the squirrel monkey (Saimiri sciureus) was exposed to 500 cercariae of Schistosoma bovis (Kenya), S. intercalation (Cameroon), S. mattheei (South Africa), 2 strains of S. mansoni (Puerto Rico and South Africa), 2 strains of S. rodhaini (Uganda and Kenya), and Schistosomatium douthitti (North America). It is apparent that the squirrel monkey can be employed as an experimental host for a broad range of mammalian schistosomes. Based upon cercariae-adult worm ratios, it is a good host for S. intercalatum, S. mattheei, the Puerto Rico and South Africa strains of S. mansoni, and Schistosomatium, but only a fair host for S. bovis and the Uganda and Kenya strains of S. rodhaini. Individuality of host-parasite relationships is borne out by the great ranges recorded for egg deposits in different organs as well as by total body egg counts and eggs/worm pair.     

Comparison of Reproductive Characteristics and Changes in Body Weight Between Captive Populations of Rufous and Gray Mouse Lemurs

The nocturnal Malagasy mouse lemurs are among the smallest primates worldwide. Several sibling species are known. Of these, the rufous and the gray mouse lemur differ with respect to morphology, genetics, and communication. They might also differ in seasonal reproduction and body weight changes. We investigated and compared reproductive activities and changes in monthly body weight in males and females of successfully breeding colonies of both species under the same photoperiodic conditions. Females of both species showed estrous cycles only during the long-day period. Rufous mouse lemur females seemed to have a shorter gestation than their sibling species (57 vs. 62 days). The number of estrous cycles (2.25 vs. 2.5/season) and their lengths (59 vs. 52 days) were similar. Litter size (2) seemed to be similar. Latency of estrous occurrence after photoperiodic stimulation was longer in Microcebus rufus than in its sibling species (71.6 and 42.3 days). The same was true for the onset of the growth of the testes. The rate of growth and size of the testes were similar, and precede the estrous onset in both species. The reproductive activity was shorter in both sexes of the rufous than of the gray mouse lemurs. In both species, body weight showed similar seasonal changes. Males lost more weight during the breeding season than females did. In rufous mouse lemurs, body weight was similar in both sexes during the nonbreeding season. In gray mouse lemurs, sexes differed throughout the year.     

Recognition of order effects in squirrel monkey antiphonal call sequences

Squirrel monkeys exchange chuck vocalizations in antiphonal sequences that suggest a request for information, and a response to that request. Chucks are characterized by measurable acoustic differences, notably in peak frequency, related to their position in a sequence. To determine the cues by which animals might identify a chuck that is a request for information from one that is a response, first-in-sequence (α) and second-in-sequence (β) chucks, differing in peak frequency, were recorded from familiar individuals and strangers. These chucks, and a sham control, were played back, in the temporal context of a first-in-sequence call, to a target group of socially housed captive squirrel monkeys. Animals responded more strongly to α chucks than to β chucks for calls originating from familiar individuals. No distinction was made between the α and β chucks of strangers, and all strangers' chucks got a weaker response than did familiar α chucks. Squirrel monkeys probably use acoustic differences, rather than context, to discriminate the ordinal significance of a chuck, but cannot do so unless they are familiar with the caller. © 1993 Wiley-Liss, Inc.