Sperm parameters and testicular volumes in Saguinus mystax

Adult male Saguinus mystax tamarins were evaluated for sperm parameters and testicular volumes. Sperm concentrations average 195.5 X 10(6)/cc with 41.7% motile sperm. Semen specimens were classified as normal, relative to sperm morphology, when 95% or more of the sperm in the specimen had normal morphology; 76% of the animals evaluated had normal semen specimens using this criterion. Testicular volumes averaged 726.9 mm3. A total of 50 infants were sired by 16 of these males during the period covered by this report.     

Reactions of wild tamarins,Saguinus mystax andSaguinus fuscicollis to avian predators

During a field study in northeastern Peru, the reactions of a group ofSaguinus mystax on Padre Isla and of a mixed-species troop ofS. mystax andSaguinus fuscicollis at the Río Blanco to raptorial and other birds were observed. Alarms that are specific to flying stimuli were elicited by birds of prey, but other birds that do not represent a threat to the tamarins also caused alarm calls. Alarm events (i.e., instances when one or more alarm calls were given) were observed at rates of 0.3/hr (Padre Isla) and 0.5/hr (Río Blanco). Rates of alarm events significantly increased after the birth of an infant in the Padre Isla group and after the attack of an ornate hawk-eagle (Spizaetus ornatus) on the Río Blanco group. Reactions to alarming stimuli/alarm calls ranged from looking up to falling down from trees. The modification of the tamarins' behavior by the potential presence of aerial predators indicates that raptors represent an important predatory threat to tamarins.     

Evaluation of serum parameters relevant to vitamin D status in tamarins

Serum levels of 25(OH)D, alkaline phosphatase (AP), and parathormone (PTH) were evaluated to investigate the vitamin D requirement of Saguinus fuscicollis. Diets with various vitamin D content were fed 4 weeks and longer. The values of 25(OH)D (30-300 nmol/l), AP (less than 300 U/l), and PTH (less than or equal to 1,000 equl/l) considered as normal were obtained with 2,000 IU D3/kg diet, or 33 IU/animal/day, which we regard as the level required. Animals depleted of vitamin D for 215 days developed a secondary hyperparathyroidism.     

Colour discrimination learning in black-handed tamarin (<Emphasis Type="Italic">Saguinus midas niger</Emphasis>)

Colour is one cue that monkeys use for perceptual segregation of targets and to identify food resources. For fruit-eating primates such as Saguinus, an accurate colour perception would be advantageous to help find ripe fruits at distance. The colour vision abilities of black-handed tamarins (Saguinus midas niger) were assessed through a discrimination learning paradigm using Munsell colour chips as stimuli. Pairs of chips were chosen from an early experiment with protan and deutan humans. The monkeys (three males and one female) were tested with stimuli of the same hue, but different brightness values, in order to make sure that discriminations were based on colour rather than brightness cues. The results showed that the female, but not the males, presented an above-chance performance for stimuli resembling hue conditions under which tamarins forage (oranges vs greens). Colour vision in S. m. niger is discussed according to the advantages and disadvantages of dichromatism in daily search for food as well as to aspects regarding polymorphism in New World monkeys.     

Social implications of gummivory in marmosets

Gummivory or exudate feeding is a major dietary specialization which has received relatively little attention in the literature. While plant exudates contribute to the diet of many primate species, we suggest that the callitrichid species Cebuella pygmaea and Callithrix jacchus are obligate exudate feeders under free-ranging conditions. Callithrix jacchus provides an excellent model for examining the effects of exudate feeding and foraging upon social behavior, since other callitrichid species of similar body size do not share this dietary specialization. We review the effects of exudate foraging on specific social behaviors observed both in field and laboratory populations of C. jacchus. By comparing this species to closely related species, exudate foraging is seen to (1) be retained under laboratory conditions, (2) increase the frequency of territorial marking behavior while decreasing the frequency of overt aggression in males, (3) decrease the duration of infant care, and (4) increase the number of nonadults in social groups but not affect group size. The evidence presented supports the hypothesis that the consequences of exudate foraging in C. jacchus are fundamental and socially complex. © 1994 Wiley-Liss, Inc.     

The ecological role of the callitrichidae: a review

The marmosets and tamarins fill a unique ecological role among the anthropoid primates, one that has not been fully recognized. Many misconceptions--that they are primitive, monogamous, territorial, and squirrellike--pervade the literature. These misconceptions are largely the result of misinterpreting laboratory studies which have not been confirmed with identified animals in natural habitats. Recent field studies, reviewed here, indicate that marmosets and tamarins have a highly derived ecological role, are not monogamous, feed largely on insects and plant exudates, and have uniquely specialized positional behavior involving clinging to vertical tree trunks in order to feed on exudates. Accompanying these behavioral traits are a number clawlike nails on all digits except the hallux, and a three-cusped upper molar morphology. These form a suite of characteristics unique among the living primates, many of which are related to their ecological role. We believe that the marmosets and tamarins are members of a guild of exudate feeders in which plant exudates are an important component of the diet. It is within this framework of a primate foraging guild that we can best understand many of their morphological and behavioral adaptations.     

Functional implications of skeletal diversity in two South American tamarins

This study examines the relationship between positional behavior and morphology for two closely related South American tamarin species, Saguinus fuscicollis illigeri and Saguinus oedipus oedipus. Although never systematically documented, the two species are suspected of exhibiting highly similar yet subtly different locomotor behaviors with a greater propensity for climbing, springing, and more powerful leaping in S. oedipus. Fourteen measurements reflecting biomechanical structuring were taken from the postcranial skeleton of 28 individuals of each species. The data were reduced to principal component scores and subjected to a multiple analysis of variance to determine the extent of intergroup skeletal variation. Areas of significant skeletal diversity were interpreted functionally. The results suggest that the differences in functional patterning among the two species is consistent with the behavioral hypothesis. It is concluded that subtle changes in positional behavior may be capable of altering skeletal morphology.     

Vertical clinging, small body size, and the evolution of feeding adaptations in the Callitrichinae.

Primates of the subfamily Callitrichinae (Callimico, Callithrix, Leontopithecus, and Saguinus) are small-bodied New World monkeys (105-700 g) possessing clawlike nails on all manual and pedal digits excluding the hallux. Specialized nails in these genera serve a critical function in feeding by enabling tamarins and marmosets to cling to trunks and other large vertical supports while exploiting food resources. Within the subfamily, there is evidence of at least four distinct large-branch feeding patterns. These include (1) seasonal exudate feeding and occasional trunk foraging (many Saguinus spp.); (2) exploitation of bark surface insects and the use of trunks as a platform to locate terrestrial prey (Saguinus fuscicollis, S. nigricollis, and Callimico); (3) manipulative foraging and bark stripping to locate concealed insects and small vertebrates (Leontopithecus); and (4) tree gouging and year-round exudate feeding (many Callithrix). Large-branch feeding and the use of vertical clinging postures appear to be a primary adaptation among virtually all callitrichines, distinguishing them ecologically from other platyrrhine taxa. Given the anatomy and behavior of extant callitrichines, Saguinus appears to be the most ecologically generalized member of this subfamily, and species of this genus may provide useful models for reconstructing the feeding and foraging adaptations of early callitrichines.     

Body weights in mixed species troops of Saguinus mystax mystax and Saguinus fuscicollis nigrifrons in Amazonian Peru

An investigation of body weights of members of mixed species troops of Saguinus mystax mystax and Saguinus fuscicollis nigrifrons was conducted at the Rio Blanco Research Station in northeastern Peru. A total of 107 adult and subadult tamarin monkeys were trapped, measured, and released. Data collected indicate that mean body weights for adult male and female moustached tamarins are 564 gm and 626 gm, respectively, whereas for adult saddle-back tamarins these values are 412 gm and 411 gm. Subadults weighed 11-27% less than adults. Body weights recorded in this study are significantly greater than those previously reported for tamarins of the same species and age living in other areas of Amazonian Peru. We hypothesize that, in the case of moustached and saddle-back tamarins, advantages associated with feeding and foraging in mixed species troops facilitate greater efficiency in resource monitoring and result in the maintenance of larger body weights.