Development of responsiveness to novel objects in the titi monkey,Callicebus moloch

Adult titi monkeys react to novelty more strongly and cautiously than other New World primates. Developmental changes in responsiveness were assessed by presenting complex novel objects to family groups consisting of 11 male-female pairs and their adult (31–33 months), subadult (20–23 months), and juvenile offspring (10–16 months). Food and a simple block were included as control conditions. Differences in attraction to novel objects were inversely related to age. Juveniles approached more objects, more quickly, and spent more time near them than older subjects. Parents, the least responsive age-group, seemed more indifferent than cautious. Age-effects were smaller with the block, and negligible with food. Even in the most responsive age-group, investigatory behavior appeared subdued as compared to other primate species. sensuHershkovitz, 1963.     

Vocal regulation of inter- and intragroup spacing during boundary encounters in the titi monkey,Callicebus moloch

Monogamous primates maintain exclusive use of their ranges by regularly defining and reinforcing the conventional location of boundaries.Callicebus moloch males often call alone during the first morning bout, when groups are near boundaries but usually separated by more than 100m. Depending on the location and proximity of neighboring animals, groups might begin duetting and approaching one another. Duetting requires close vocal and spatial coordination of the mated pair, and stimulates the approach of neighboring pairs. At the boundary, vocalizations which keep the pair together and those associated with withdrawal from the boundary increase in proportion. To determine the effect of different calls, I played back recordings of six different vocalizations during two playback experiments, holding location and proximity constant. The responses supported hypotheses generated in the normalistic study, and suggested that at the boundary aggression is primarily intrasexual. Vocalizations and their effects in specified contexts constitute the mechanisms regulating spacing. The resulting spacing patterns maintain resource availability and exclusive access to a mate.     

Karyotypic study of titi monkeys,Callicebus moloch brunneus

A karyotypic study on a subspecies of the dusky titi,Callicebus moloch brunneus, was carried out and a third karyotype ofC. moloch was discovered. The chromosome number of this subspecies is 48. The autosomes consist of 5 subtelocentric, 5 submeta- or metacentric, and 13 acrocentric chromosome pairs. The X chromosome and the Y chromosome are submetacentric and metacentric, respectively. A comparative study with other subspecies of theC. moloch group (i.e.,C. m. cupreus andC. m. ornatus with 2n=46 andC. m. donacophilus with 2n=50) suggests that the karyotype ofbrunneus occupies a position intermediate between the two other karyotypes ofC. moloch, but nearer to that of 2n=50. The presumed total differences betweenbrunneus andcupreus comprise one Robertsonian rearrangement, one centromeric transposition and four pericentric inversions, and those betweenbrunneus anddonacophilus involve one translocation or breakage (possibly corresponding to two events, that is, one Robertsonian rearrangement and one centromeric transposition).     

The pairbond in the titi monkey (Callicebus moloch): intrinsic versus extrinsic contributions of the pairmates

Aspects of a monogamous relationship can be inferred by observing reactions of mated individuals to unfamiliar conspecifics. The present study examined the behaviours shown by male and female titi monkeys (Callicebus moloch) toward an opposite-sex stranger, and the effect of their pairmate's absence or presence on these encounters. Behaviours within unfamiliar heterosexual pairs showed superficial similarities to behaviours of mated pairs. Although there were few affiliative behaviours between unfamiliar individuals, animals were often in spatial proximity and even performed sexual behaviour. The visual presence of a pairmate clearly affected encounters between unfamiliar heterosexual pairs in several respects. The presence of a male pairmate had a much stronger influence on all behavioural measures compared to the presence of a female pairmate. Possible functional aspects of these results are discussed.     

Effects of duration of separation on responses to mates and strangers in the monogamous titi monkey (Callicebus moloch)

Adult male and female titi monkeys form an intense social bond characterized by high levels of affiliative interactions between pairmates and agonistic responses to strangers. In natural settings, separation between mates can vary from brief periods, as when mates drift apart during feeding, to permanent separation, occasioned by desertion or death. In this study we asked how different durations of separation altered the behavior of male and female titi monkeys (Callicebus moloch). We compared the effects of brief separation such as might occur incidentally during feeding (1–2 h) with prolonged separation such as might occur if one partner died or deserted (5 days). Effects were observed during a 30 min reunion of pairmates or during a 30 min encounter with a stranger of the opposite sex. Following brief separation, interactions between mates and between strangers clearly differed in measures of affiliation, but not in behaviors indicative of arousal. Following prolonged separation, measures of arousal increased with both mated pairs and strangers. Females tended to interact more readily with a stranger following prolonged separation than after brief separation, but interactions between mates were essentially unchanged and differed substantially from those between strangers. The data suggest that the pair bond persists in titi monkeys after prolonged social isolation, despite increased interest in interacting with potential new partners. Am. J. Primatol. 43:225–237, 1997. © 1997 Wiley-Liss, Inc.     

Craniofacial sexual dimorphism in Alouatta palliata, the mantled howling monkey

Ontogenetic scaling has been hailed as an explanation of the differences in craniofacial morphology between adult males and females of a number of non human primate species. This inference has implications for the evolutionary processes underlying patterns of sexual variation, as several heterochronic processes (rate and time hypo- and hypermorphosis) predict ontogenetic scaling. Primary among species for which ontogenetic scaling of craniofacial dimensions has been claimed is Alouatta palliata , the mantled howling monkey. This study uses a variety of analytical tools to explore the efficacy of ontogenetic scaling as an explanatory paradigm for this classic example. Multivariate analysis captures shape far better than does bivariate analysis. However, multivariate analysis does not support the traditional inference of ontogenetic scaling. Explanations for contradictory results are considered.     

Developmental changes in responsiveness to parents and unfamiliar adults in a monogamous monkey (Callicebus moloch)

Titi monkeys (Callicebus moloch) are monogamous New World primates that are characteristically found in family-type groups consisting of a mated adult pair and one or two young. The factors maintaining the small size of these groups are not known. Based on observations of free-ranging and captive families, parental aggression toward older offspring seems unlikely to play a significant role. Maturing individuals themselves, however, could undergo behavioral changes that weaken ties to their natal group. These might include waning of affiliative relations with parents, or subtle forms of aversion. Independent of such changes, increasing interest in unfamiliar conspecifics could be a factor. We examined these possibilities in the present study by assessing changes in social behavior and social preferences from initial ambulatory independence (6 months) through reproductive maturity (24 months) in a combined cross-sectional/longitudinal study of 21 captive titi monkeys living with their parents. Responses to both parents and to an unfamiliar adult heterosexual pair, a single unfamiliar adult male, and a single unfamiliar adult female were observed when subjects were given a choice between parents and strangers presented simultaneously or as the only social incentive. Social stimuli were at opposite ends of a 16.8-m-long test corridor. Subjects could move freely about the corridor for 5 min with each configuration of social stimuli. They stayed closer to parents than to strangers at all ages. Responsiveness to strangers increased with age and suggested growing ambivalence, particularly toward the male stranger. As they approached 24 months of age, male subjects showed a dramatic increase in the frequency and intensity of agonistic behaviors toward male strangers, behaviors that were rarely directed toward female strangers or parents. Waning of attraction to parents may be less important in dispersal from the natal group than changing reactions to strangers.     

Communication in the Titi monkey, Callicebus

The communication system of Callicebus moloch includes a few olfactory and tactile signals, a moderate number of visual signals, and an enormous number of acoustic signals. The visual signal repertory is comparatively simple, and may be primitive in some respects. The acoustic signal repertory is very complex. It may illustrate the maximum elaboration which can beattained by species-specific language.     

Structural aspects of arboreality in titi monkeys (Callicebus moloch)

In nature titi monkeys spend virtually all of their time in trees. Preferences for certain heights above the ground or for trees per se are probably not, however, the immediate causes of this behavior, for animals housed in a large field cage containing many trees spend most of their time on a low-altitude artificial runway system. Further, the animals are not necessarily reluctant to touch the ground. To investigate the importance of perceived substrate structure as a determinant of arboreality, individuals were given opportunities to descend from their home runway and travel to food placed nearby on the ground. The animals travelled along a schematic model of a tree branch rather than across open ground when given a choice of these substrates, but they readily crossed the open ground when it was their only travel option. When the schematic model increased substantially in length and no longer provided a short route to food, it was still the preferred substrate. The results suggest that an abstract representation of a tree branch attracts and guides locomotion in titis, and that responsiveness to substrate characteristics contributes to arboreality in this species.     

Reproductive biology of female titi monkeys (Callicebus moloch) in captivity

Titi monkeys (Callicebus spp., Cebidae) are monogamous neotropical primates that live in family-like groups typically consisting of an adult monogamous pair and one or two young. Knowledge about the reproductive biology of this genus is scanty. This study investigated the reproductive biology of female dusky titi monkeys (Callicebus moloch). An initial analysis characterized reproductive parameters of 32 females from a captive colony maintained for 23 years at the California Regional Primate Research Center (CRPRC). The colony records provided data on reproductive parameters such as interbirth intervals, seasonality, age at first pregnancy, and reproductive rate in captivity. Changes in urinary levels of estrone conjugates (E1C) and pregnanediol-3alpha-glucuronide (PdG) were used to characterize major reproductive events. Urine samples from eleven females were collected during 17 months. The endocrine data were used to examine changes associated with cycling, conception, and the post-partum period as well as to determine the duration of the ovarian cycle and gestation length. The analysis of colony records indicated that females whose infant survived through weaning gave birth at intervals remarkably close to one year, while those who lost their offspring showed a significantly shorter interval. As long as they lived within the family group, mature female offspring did not breed. The analysis of the endocrine profiles indicated that after giving birth to a viable offspring, females undergo a relatively prolonged period of anovulation (approx. 6.5 months), followed by 1-3 non-conceptive cycles (approx. 1 month), after which they conceive and gestate (4.3 months).     

An Analysis of the Organization of Vocal Communication in the Titi Monkey Callicebus moloch

Vocalizations of titi monkeys were recorded from 6 groups at two sites in the llanos of Colombia during 8 months of study. Frequency and temporal measurements from spectrograms of recordings, and differences in their patterns of use, were used to characterize call types. Animals repeat calls to form phrases, and combine phrases to form sequences. The six sequence types, defined by different transition probabilities between phrases, varied in proportion in different contexts. To examine the effect of order of phrases on response, I played back artificially constructed sequences to subject groups. I discuss hierarchical and sequential mechanisms as generators' of vocal sequences, and draw comparisons with models of human language.     

Activity pattern of the masked titi monkey,Callicebus personatus

A group of six masked titi monkeys was studied at the Sooretama Biological Reserve, Espírito Santo, Brazil. The family group consisted of adult male and female, three juvenile-subadult offspring, and an infant carried by the father. Two patterns of activity were identified: one in which two major feeding peaks were separated by a single long rest period and a relatively long travel distance between the two major feeding sites; and a second in which three major feeding peaks were separated by rest periods and travel was more evenly dispersed throughout the day.Callicebus personatus was similar toC. moloch in the folivorous supplementation of its frugivorous diet, and in having marked daily peaks in feeding and resting activities.C. personatus was similar toC. torquatus in the location of sleeping position on a large open bough, and the habit of calling from well within the territorial boundary. All three species are known to live in monogamous family units with parental care by the adult male, defend territories with loud intergroup vocalizations, and feed primarily upon a small number of widely dispersed fruits.     

Divergence between biochemical and cytogenetic differences in three species of the Callicebus moloch group

Specimens from three species of the Callicebus moloch group—C. Moloch (N = 80), C. brunneus (N = 166), and C. cupreus (N = 23)—were studied. Twenty genetic loci were investigated through electrophoresis, genetic distances were estimated, and the results compared with the available cytogenetic data. Low values of genetic distance were encountered, contrasting with relatively large chromosome differences. We propose that recent karyotypic rearrangements, rather than other Pleistocene events, were the major evolutionary mechanisms determining speciation in these three taxa. © 1993 Wiley-Liss, Inc.     

Longitudinal observations of care and development of infant titi monkeys (Callicebus moloch)

The purpose of this study was to describe patterns of infant care and development in family groups of the monogamous titi (Callicebus moloch). Three infant titis were observed with their natal family groups over the first six months of life. Field observations of extensive male involvement with infants were confirmed. Adult males were clearly the infants' primary social companions, and infants spent more time in contact with adult males at all ages than with mothers or older siblings. However, mothers and siblings also carried infants at times and interacted with them in affiliative ways (e.g., grooming, nuzzling, play). Mothers often invited nursing, but otherwise it was infants who primarily initiated transfers between carriers and approaches to parents, reminding us that the infants' own activities and their effects on caregivers should not be overlooked in considerations of the patterns of infant care. This is particularly important for those species exhibiting extensive parental involvement by males. It is suggested that substantial male care of young titi infants leads to several important consequences for the infant's social development, including the development of a stronger attachment to the father than the mother.     

Biometrical studies upon hominoid teeth: the coefficient of variation, sexual dimorphism and questions of phylogenetic relationship

Sexual dimorphism as a function of variation in hominoid tooth metrics has been investigated for four groups of taxa: Recent great apes (two subfamilies), Dryopiths (one subfamily), Ramapiths (one subfamily) and hominids (one family). Gorilla, and to a lesser extent Pan, appear characterized by very high levels of sexual dimorphism and meet several criteria for statistical outliers. Recent great apes are the only group exhibiting consistently high levels of sexual dimorphism. Ramapiths are the only group characterized by low levels of sexual dimorphism and their relative canine length is most similar to Dryopiths. Both Dryopiths and hominids contain taxa with low and intermediate levels of sexual dimorphism. The Gingerich and Shoeninger hypothesis relating coefficients of variation to occlusal complexity is supported. Non-parametric statistics suggest that homogeneity of coefficient of variation profiles over most of the tooth row is characteristic of only the Dryopiths and a composite data set composed of the Dryopith plus Ramapith tooth measurements. Oxnard's model for the multifactorial basis of multiple sexual dimorphisms is also supported. The Dryopith and hominid patterns of sexual dimorphism are similar, an observation that suggests phylogenetic relationship. At the taxonomic level of subfamily or family, sexual dimorphism is a character of cladistic usefulness and possible phylogenetic valence. Assuming that breeding system and sexual dimorphism are functional correlates as many workers suggest, then Ramapithecus sp. China, Sivapithecus indicus and possibly Australopithecus boisei are good candidates for having possessed monogamous breeding/social structures. All Dryopith taxa, S. sivalensis, Sivapithecus sp. China, A. afarensis, Homo habilis and H. erectus emerge as the best candidates for having possessed a polygynous breeding/social structure. No biometrical affinities of Ramapiths with hominids can be demonstrated and some phylogenetic relationship with Dryopiths is suggested. Kay's interpretation of Ramapith sexual dimorphism and taxonomic affinity is not supported. The lack of control over temporal and geographic range variation is discussed and the loose association of these variables with differences in tooth morphology is noted. The high heritability of tooth size also suggests that assignment of "high" or "low" index values to extinct taxa as a measure that describes evolving clades at discrete points in evolutionary time is appropriate.(ABSTRACT TRUNCATED AT 400 WORDS)     

Ontogenic changes and sexual dimorphism in the head, mouth and teeth of the lesser spotted dogfish

Male Scyliorhinus canicula possess a longer and narrower mouth than females resulting in pronouced sexual dimorphism with respect to the mouth length/mouth width ratio (0.49 and 0.43, respectively). Significant sexual differences in the girth of the head and pre-oral, pre-branchial and head lengths were also recorded. Males were found to have longer teeth than females. Reasons for these differences are discussed.