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Simian foamy viruses (SFVs) infect most nonhuman primate species and appears to co-evolve with its hosts. This co-evolutionary signal is particularly strong among great apes, including orangutans (genus Pongo). Previous studies have identified three distinct orangutan SFV clades. The first of these three clades is composed of SFV from P. abelii from Sumatra, the second consists of SFV from P. pygmaeus from Borneo, while the third clade is mixed, comprising an SFV strain found in both species of orangutan. The existence of the mixed clade has been attributed to an expansion of P. pygmaeus into Sumatra following the Mount Toba super-volcanic eruption about 73,000years ago. Divergence dating, however, has yet to be performed to establish a temporal association with the Toba eruption. Here, we use a Bayesian framework and a relaxed molecular clock model with fossil calibrations to test the Toba hypothesis and to gain a more complete understanding of the evolutionary history of orangutan SFV. As with previous studies, our results show a similar three-clade orangutan SFV phylogeny, along with strong statistical support for SFV-host co-evolution in orangutans. Using Bayesian inference, we date the origin of orangutan SFV to >4.7 million years ago (mya), while the mixed species clade dates to approximately 1.7mya, >1.6 million years older than the Toba super-eruption. These results, combined with fossil and paleogeographic evidence, suggest that the origin of SFV in Sumatran and Bornean orangutans, including the mixed species clade, likely occurred on the mainland of Indo-China during the Late Pliocene and Calabrian stage of the Pleistocene, respectively., (Copyright © 2017 Elsevier B.V. All rights reserved.)

An immature crab-eating macaque (Macaca fascicularis), which was sitting on the river bank near the Orangutan Research and Conservation Project base camp in the Tanjung Puting Reserve, Kalimantan Tengah, Indonesia, was seized by a crocodile which rapidly emerged from the water and then resubmerged with the monkey in its jaws. As crocodile populations are in a decline throughout Borneo, crocodile predation on crab-eating macaques was probably more frequent in the past. This predation may have influenced development of some behaviors with an antipredator function in M. fascicularis., (Copyright © 1984 Wiley‐Liss, Inc., A Wiley Company.)

During a four-year period at Tanjung Puting Reserve, Central Indonesian Borneo, subadult males were observed for 670.5 observation hours, 463 hours of which were as focal individuals. Subadult males were quite gregarious, participating in groupings for 40.9% of the time they were observed as targets. Subadult male sociality centered around females; 83% of the time subadult males spent in groupings was exclusively with females, as compared to 3% of contact time spent exclusively with other males. Much subadult male sociality can be understood in terms of male-male competition for females. Interactions between adult and subadult males were almost entirely determined by the presence or absence of females. Adult males were more belligerent when females were present. Twenty-two copulations or attempted copulations occurred during 16 subadult male-female encounters, two of which were consortships. The majority of subadult male copulations (86%) were resisted matings. Outside of consortship, resisted matings (or the first in a series of resisted matings or attempts) usually took place at encounter or shortly thereafter. Subadult males also surreptitiously followed adult males and their consorts. Subadults frequently located receptive females before adult males did but were replaced by adult males when these appeared. Subadult male reproductive strategy consisted of both sneak/"rape" and consort tactics with sneak/"rape" predominating., (Copyright © 1985 Wiley‐Liss, Inc., A Wiley Company.)

During a four-year period, more than 6,800 hours of observation were collected on 58 individually recognized wild orangutans in a 35-km 2 study area at the Tanjung Puting Reserve, Kalimantan Tengah (Central Indonesian Borneo). As in other areas, although small temporary associations of orangutans recurred, the basic units of populations consisted of (1) adult males, (2) adult females with one or two dependent offspring, and (3) independent immatures (adolescent males and females and subadult males) with units predominantly solitary. However, independent immatures were more gregarious and social than adults. Adolescent females in particular spent more time in groupings than did adult females. Although successfully consorting adult males might spend up to 22% of time observed in association with other orangutans, adult males were the least social of all age/sex classes once consortships were excluded. Ninety percent of their participation in social groupings consisted of sexual consortships. Adult males were totally intolerant of each other; only four encounters between adult males were observed. All involved avoidance or aggression, including one lengthy combat. Adult females were solitary but social and participated in a variety of groupings. However, with the exception of adult females briefly following consorting couples, nonreceptive adult females did not initiate or maintain social contact with orangutans other than adult females. Comparisons with results of studies from other areas indicate that, once samples used in each study are made explicit and aggregations owing to chance encounters at major food sources excluded, orangutan sociality seems relatively consistent over the entire range in which the species is found. Bornean orangutans are not as totally asocial as the first studies in the wild indicated. In fact, it would probably be better to characterize wild orangutans as semisolitary, rather than solitary., (Copyright © 1985 Wiley-Liss, Inc., A Wiley Company.)