Vocal Communication in a Fission-Fusion Society: Do Spider Monkeys Stay in Touch With Close Associates?

In fission-fusion societies, in which animals from the same group may spend long periods of time apart from each other, individuals could use long-distance vocalizations to maintain contact with others. This could be achieved with vocalizations that simply carried information about the caller's identity and location. I explored this possibility using observations and experiments from a 3-year field study of spider monkeys (Ateles geoffroyi) in Punta Laguna, México, analyzing the use of the species' most frequent vocalization, the whinny. By following 2 subgroups simultaneously, I found that subgroups that were within the active space of the whinny approached each other more often than subgroups that were farther apart. Individual adults in these subgroups also emitted more whinnies when they were within hearing range of another subgroup than when farther apart. I used a paired playback design to determine whether whinnies could influence the behavior of close associates as opposed to nonassociated individuals. Although nonassociates were as likely as close associates to respond vocally to playbacks of whinnies, only a close associate ever approached the speaker. Collectively, the results suggest that whinnies are used by spider monkeys to achieve flexibility in spacing while maintaining specific social relationships.     

Embraces and Grooming in Captive Spider Monkeys

Relatively little information is available regarding the role of social grooming and embraces in spider monkeys that live in fission-fusion societies in which individuals are usually split into subgroups. We investigated whether embraces and grooming have similar roles in captive spider monkeys by examining their occurrence in two contexts. One context was fusion, i.e. when the monkeys moved into an area of the enclosure where other monkeys were present, in which individuals from different subgroups were expected to exchange greeting behavior. The other context was the access to young infants, in which females were expected increase their friendly behavior toward mothers. We collected data by observing all individuals within a subgroup and via focal animal sampling. We found that overall embraces occurred more frequently than grooming and that their distributions were not correlated. The frequency of embraces was positively associated with the number of fusion events per observation, whereas the frequency of grooming bouts was not. Furthermore, embraces were more frequent following initial approaches after fusion versus subsequent approaches, and the figure was higher than the corresponding one for grooming. Mothers received more embraces after than before the birth of their infants, whereas there was no such effect for grooming. Embraces, but not grooming, play a role in the regulation of social relationships in spider monkeys. Embraces may serve as signals of benign disposition in contexts that are likely to be associated with tension, such as fusion and access to infants.     

Extensive enlargement of the maxillary sinus in Alouatta caraya (mammalia, primates, cebidae): an allometric approach to skull pneumatization in Atelinae

In contrast to the paranasal sinuses of Old World monkeys and hominoids, little information is available about the paranasal sinuses of New World monkeys. Because this information is crucial in order to draw further conclusions about the evolution and biological role of skull pneumatization, this study investigates the morphology of the paranasal sinuses in adult black-and-gold howler monkeys (Alouatta caraya). Volumes of the paranasal sinuses were calculated using computer software (SURFdriver or Allegro) from serial coronal CT scans of 20 skulls of both sexes. Skull pneumatization in A. caraya is more complex than in other higher primates. In both sexes, the maxillary sinus (MS) is the only pneumatic cavity and enlarges regularly into neighboring bones such as the frontal bone and the basisphenoid. The resulting pansinus is often partitioned by several vertical septa. As in most external cranial dimensions, mean MS volume of A. caraya (male 4.08 cm(3); female 2.00 cm(3)) shows significant sexual dimorphism. Reduced major axis regression analysis between MS volume and different cranial dimensions for A. caraya (and for available data from other platyrrhines) suggests a distinct association for this group, with Alouatta having one of the largest pneumatic cavities. The combination of this unusual expansion of the MS of Alouatta and the occurrence of distinct septa within the sinus may be a consequence of the distinct skull architecture of Alouatta.     

Group size in folivorous primates: ecological constraints and the possible influence of social factors

The ecological-constraints model assumes that food items occur in depletable patches and proposes that an increase in group size leads to increased day range due to more rapid patch depletion. Smaller groups become advantageous when an increase in travel costs is not repaid by an increase in energy gained or some other fitness advantage. On the other hand, we also know that group size can be influenced by social factors. Here we contrast the diet and group size of red colobus (Procolobus badius) and black-and-white colobus (Colobus guereza) in Kibale National Park, Uganda to consider how ecological and social factors are affecting their group sizes. Subsequently, we examine whether the insights gained from this detailed comparison can provide an understanding of why the social organization and group size of mantled howlers (Alouatta palliata) and black howlers (A. pigra) differ. Two groups of red colobus and two groups of black-and-white colobus were studied over 10 months. Red colobus groups were larger (48 and 24) than black-and-white colobus groups (9 and 6). The two groups of red colobus overlap home ranges with the two groups of black-and-white colobus; 75% and 95% of their home ranges were within red colobuss home range. There was a great deal of similarity in the plant parts eaten by the two species and both species fed primarily on young leaves (red colobus 70%, black-and-white colobus 76%). In terms of the actual species consumed, again there was a great deal of similarity between species. The average dietary overlap among months for the two neighboring groups of red colobus was 37.3%, while the dietary overlap between the red colobus and the black-and-white colobus group that had its home range almost entirely within the home range of the red colobus groups averaged 43.2% among months. If ecological conditions were responsible for the difference in group size between the two colobine species, one would expect the density of food trees to be lower in the home ranges of the black-and-white colobus monkeys, since they have the smaller group size. We found the opposite to be true. Both black-and-white colobus groups had more food trees and the cumulative size of those trees was greater than those in the red colobuss home ranges. We quantify how these differences parallel differences in mantled and black howlers. The average group size for mantled howlers was 12.9 individuals, and for black howlers it was 5.3 individuals. We explore possible social constraints, such as infanticide, that prevent black-and-white colobus and black howlers from living in large groups.This revised version was published online in April 2005 with corrections to the cover date of the issue.     

Three spontaneous lymphomas in a colony of cotton-top tamarins (Saguinus oedipus)

Cotton-top tamarins are well known for their prevalence to idiopathic colitis and adenocarcinomas. At the same time, information on the incidence of spontaneous lymphomas in this highly endangered species is rare. Records, 212 in total, of cotton-top tamarins (Saguinus oedipus) necropsied at the German Primate Centre between 1979 and 1998 were viewed to establish the prevalence of lymphoid neoplasms. Neoplastic lymphoid cell growth was mentioned in three necropsy records. Immunohistology was performed in all three cases on the remaining formalin-fixed, paraffin-embedded tissue using antibodies against CD20, CD3, lysozyme, Ki-67, IgM, IgG, kappa, lambda and EBNA-2. Combining histological and immunohistological results, the lymphomas could be differentiated into two low-grade T-cell lymphomas and one high-grade multicentric polymorphic B-cell lymphoma. This corresponds to a 1.4% incidence of lymphomas in our cotton-top tamarin population over a period of 19 years. Although frozen material was not available and virological testing could not be carried out, clinical or histological evidence did not support an aetiological role of Herpes (H.) saimiri, H. ateles, simian T-cell leukaemia virus type 1 (STLV-1) or Epstein-Barr-related herpesvirus in any of these cases. The lymphomas were considered to be spontaneous.     

Immunolocalization of proliferating cell nuclear antigen (PCNA) in cynomolgus monkey (Macaca fascicularis) testes during postnatal development

The age-related distribution of proliferating cell nuclear antigen (PCNA) in the testes of cynomolgus monkeys (Macaca fascicularis) during postnatal development was detected using light-microscopic immunohistochemistry. In neonatal testes, some PCNA-positive spermatogonia, Sertoli cells, peritubular cells, and Leydig cells were detected. In early infantile testes, only a few of these cell types were positive. In late infantile testes, the numbers of positive cells were greater than in the earlier developmental stages. In pubertal testes, the numbers of positive spermatogonia, spermatocytes, Sertoli cells, peritubular cells, and Leydig cells were considerably higher. In adult testes, a larger percentage of spermatogonia and spermatocytes was positive, and peritubular cells and Leydig cells were occasionally positive; secondary spermatocytes, spermatids, and Sertoli cells were not positive. We concluded that immunolocalization of PCNA can serve as a tool for studying proliferation status in developing testes of cynomolgus monkeys. A relatively low proliferative activity in early infantile testes and a remarkable increase of proliferative activity in pubertal testes correlate with the fluctuations of steroidogenic functions during postnatal development in cynomolgus monkeys.     

Age changes in plasma IGF-1 concentration in free-ranging Japanese macaques (Macaca fuscata)

To obtain fundamental data on the endocrine background for the wild Japanese macaque (Macaca fuscata) growth profiles, we have measured plasma insulin-like growth factor 1 (IGF-1) concentrations of free-ranging and open-enclosed Japanese macaques from five different regions in their habitat. General features of the IGF-1 levels in those troops were: 1) an age-dependent increase in the young macaques and 2) distinctively higher values among several adult females. The age changes in IGF-1 levels during the adolescent period in the free-ranging Japanese macaques were similar to those in the caged Japanese macaques.     

Glade use by Olive baboons and Blue monkeys in Mount Meru Game Reserve,Tanzania

Forest glades have conservation value for primates, with interspecies differences reported. Blue monkeys (Cercopithecus mitis) are forest‐glade edge species, whereas Olive baboons (Papio anubis) prefer the open grassland of the glade interior. In this study, scan sampling was used to record the presence and absence of each species, group sizes and individual behaviours in three glade types in Mount Meru Game Reserve, Tanzania. Glade characteristics and primate usage for the three glade types were studied: five man‐made, fifteen lower natural and five upper natural glades. During 200 (3‐h morning and afternoon) observation periods, Blue monkeys and Olive baboons were observed during 43% (86/200) and 31% (62/200) of the observation periods, respectively. Blue monkeys used upper natural glades more than man‐made and lower natural; Olive baboons used man‐made glades more than lower and upper natural. Differences in glade type, in regard to vegetation, altitude and disturbance due to trail routes, influenced gladetype use and species behaviours. In conclusion, although the management practice of clearing in and around man‐made glades provides no direct conservation value for Blue monkeys, it likely reduces overuse of natural glades and human–wildlife conflict by enhancing plant species richness and diversity important to Olive baboons.