Foregut fermentation is well known to occur in a wide range of mammalian species and in a single bird species. Yet, the foregut microbial community of free-ranging, foregut-fermenting monkeys, that is, colobines, has not been investigated so far. We analysed the foregut microbiomes in four free-ranging proboscis monkeys (Nasalis larvatus) from two different tropical habitats with varying plant diversity (mangrove and riverine forests), in an individual from a semi-free-ranging setting with supplemental feeding, and in an individual from captivity, using high-throughput sequencing based on 16S ribosomal RNA genes. We found a decrease in foregut microbial diversity from a diverse natural habitat (riverine forest) to a low diverse natural habitat (mangrove forest), to human-related environments. Of a total of 2700 bacterial operational taxonomic units (OTUs) detected in all environments, only 153 OTUs were shared across all individuals, suggesting that they were not influenced by diet or habitat. These OTUs were dominated by Firmicutes and Proteobacteria. The relative abundance of the habitat-specific microbial communities showed a wide range of differences among living environments, although such bacterial communities appeared to be dominated by Firmicutes and Bacteroidetes, suggesting that those phyla are key to understanding the adaptive strategy in proboscis monkeys living in different habitats.
Morphism refer to polymorphic species, in which multiple colour variants coexist within a population. Morphism in primates is common and langurs also exhibit certain characteristics of morphism, such as conspicuous natal coats. Banded langurs (Presbytis femoralis) and dusky leaf monkey (Trachypithecus obscurus) exhibits the same characteristics of conspicuous natal coats, but these coats are only limited to infants and changed when they reached adulthood. This article reports the first discovery of rare brown morph of two adult male banded langurs and one leucistic adult female dusky leaf monkey in Malaysia. We also conducted a systematic literature search to review the diversity of morphism in leaf monkey globally.
The endangered proboscis monkey (Nasalis larvatus) is a sexually highly dimorphic Old World primate endemic to the island of Borneo. Previous studies focused mainly on its ecology and behavior, but knowledge of its vocalizations is limited. The present study provides quantified information on vocal rate and on the vocal acoustics of the prominent calls of this species. We audio-recorded vocal behavior of 10 groups over two 4-month periods at the Lower Kinabatangan Wildlife Sanctuary in Sabah, Borneo. We observed monkeys and recorded calls in evening and morning sessions at sleeping trees along riverbanks. We found no differences in the vocal rate between evening and morning observation sessions. Based on multiparametric analysis, we identified acoustic features of the four common call-types "shrieks," "honks," "roars," and "brays." "Chorus" events were also noted in which multiple callers produced a mix of vocalizations. The four call-types were distinguishable based on a combination of fundamental frequency variation, call duration, and degree of voicing. Three of the call-types can be considered as "loud calls" and are therefore deemed promising candidates for non-invasive, vocalization-based monitoring of proboscis monkeys for conservation purposes.
A group of proboscis monkeys (Nasalis larvatus) consisting of an alpha-male, six adult females, and several immatures was observed from May 2005-2006. We collected over 1,968 hr of focal data on the adult male and 1,539 hr of focal data on the six females in a forest along the Menanggul River, Sabah, Malaysia. Availability and seasonal changes in plant species consumed by the focal monkeys were determined by vegetation surveys carried out across an area of 2.15 ha along 200-500 m trails in riverine forest. A total of 188 plant species were consumed by the focal monkeys. The activity budget of members of our study group was 76.5% resting, 19.5% feeding, and 3.5% moving. Young leaves (65.9%) and fruits (25.9%) accounted for the majority of feeding time. Over 90% of fruit feeding involved the consumption of unripe fruits and in the majority of case both the fruit flesh and seeds were eaten. Although fruit eating was rare in some months, during other times of the year time fruit feeding exceeded the time devoted to young leaves. We found that monthly fruit availability was positively related to monthly fruit eating and feeding activity, and seasonal fluctuations in dietary diversity were significantly affected by fruit eating. These results suggest that fruit availability and fruit-eating behaviors are key factors that influence the activity budget of proboscis monkeys. Earlier assumptions that colobine monkeys are obligate folivores do not apply well to proboscis monkeys and certain other colobines. Our findings may help contribute to a better understanding of the dietary adaptations and feeding ecology of Asian colobines.
From May 2005-2006, selections of river crossing locations and sleeping sites used by a one-male group (BE-Group) of proboscis monkeys (Nasalis larvatus) were investigated along the Menanggul River, tributary of the Kinabatangan River, Sabah, Malaysia. The frequency of river crossings for focal monkeys in the BE-Group was significantly higher at locations with narrow branch-to-bank distances. Branch-to-bank distances were defined as the distances between the longest tree branches extending over the river and the bank of river on each side. This was measured in areas crossed by the monkeys. The focal monkeys used locations with a higher probability of successful river crossings that did not require jumping into the water and swimming across than those that did. The frequency of sleeping site usage by the BE-Group was positively correlated with the frequency of using river crossing locations by the focal monkeys. Previous reports on predation of proboscis monkeys indicate that clouded leopards (Neofelis diardi) and crocodilians (Tomistoma schlegeli and Crocodylus porosus) may be the major terrestrial and aquatic predators of these monkeys. The selection of river crossing locations by proboscis monkeys may be influenced both by the threat of these predators and the location of suitable and protected sleeping sites. Finally, sleeping sites locations that offer arboreal escape routes may protect proboscis monkeys from leopard attack.
The mating behaviors of the proboscis monkey were observed in a riverine forest along a tributary of the Kinabatangan River, Sabah, Malaysia, for a period of 30 months. Solicitation for copulation was initiated frequently by males and occasionally by females. Most copulations involved only one mount; however, some multiple-mount copulations were observed and a maximum of six mounts per copulation were recorded. The mean duration of mounts was about 27 sec. Nonsexual mounts (female-female, female-juvenile/infant, juvenile-juvenile, and juvenile-infant) were also observed. Female-female mounts occurred shortly after failed solicitations toward males were observed. Harassment by juveniles and/or infants was observed during copulation; however, these harassments apparently did not interfere with copulation. Sexual swelling was evident in 77.4% of copulating females, with copulating subadult females showing the most distinct swelling.
To understand the effects of environmental factors on a social system with multilevel society in proboscis monkey units, the temporal change of the local density of sleeping sites of monkeys was investigated along the Menanggul river from May 2005 to 2006 in Malaysia. Proboscis monkeys typically return to riverside trees for night sleeping. The sleeping site locations of a one-male unit (BE-unit) were recorded and the locations of other one-male and all-male units within 500 m of the BE-unit were verified. In addition, environmental factors (food availability, the water level of the river, and the river width) and copulation frequency of BE-unit were recorded. From the analyses of the distance from the BE-unit to the nearest neighbor unit, no spatial clumping of the sleeping sites of monkey units on a smaller scale was detected. The results of a Bayesian analysis suggest that the conditional local density around the BE-unit can be predicted by the spatial heterogeneity along the river and by the temporal change of food availability, that is, the local density of monkey units might increase due to better sleeping sites with regard to predator attacks and clumped food sources; proboscis monkeys might not exhibit high-level social organization previously reported. In addition, this study shows the importance of data analysis that considers the effects of temporal autocorrelation, because the daily measurements of longitudinal data on monkeys are not independent of each other.