Evolutionary determinants of modular societies in colobines

Modular societies are structurally characterized by nuclear one-male units (OMUs, or harems) embedded within larger relatively coherent social bands. Within the order Primates, modular societies are uncommon, found in only a few species, including humans. Asian colobines (Presbytini) principally form either unimale groups that forage independently and are often territorial, or modular associations, which range from tight bands composed of OMUs to loose neighborhoods of OMUs. A phylogenetic reconstruction of modularity in the Presbytini revealed that the single OMU pattern is probably the ancestral state while the modular pattern is derived. The selective forces favoring the evolution of modular societies have thus far been virtually unexplored. Although some ecological explanations cannot be ruled out at the moment due to lack of comparative and quantitative data, preliminary circumstantial evidence does not seem to support them. Instead, a social factor, bachelor threat, is consistent with many observations. This hypothesis argues that where the pressure from nonreproductive bachelor males is unusually high, OMUs aggregate as a means of decreasing the amount of harassment and the risk of takeovers and infanticide. A comparative test found an association between modular societies and bachelor threat, as proxied by sex ratio within social units. The concentration of modular systems in colobines may be due to their unusual ecology, which leads to unusually low intensity of scramble competition. Modular colobines rely more on nonlimiting ubiquitous resources than nonmodular ones and thus can afford to gather in bands. Moreover, by comparing the slopes of regressions between group size and daily travel distance for several groups of one modular and one nonmodular colobine, we found slopes in the nonmodular to be steeper by a factor 30, indicating that ecological constraints associated with scramble competition prevent higher level groupings in nonmodulars. Thus, modular sociality in Asian colobines may have arisen because both social benefits are substantial and ecological costs are relatively lo

Preference for male risk takers varies with relationship context and health status but not COVID risk

Risk taking is more commonly shown by males than females and has a signalling function, serving to advertise one’s intrinsic quality to prospective mates. Previous research has established that male risk takers are judged as more attractive for short-term flings than long-term relationships, but the environmental and socioeconomic context surrounding female preferences for male risk takers has been overlooked. Using a survey instrument, we examined female preferences for male risk takers across 1304 females from 47 countries. We found preferences for physical risk takers to be more pronounced in females with a bisexual orientation and females who scored high on risk proneness. Self-reported health was positively associated with preferences for high risk takers as short-term mates, but the effect was moderated by country-level health, i.e. the association was stronger in countries with poorer health. The security provided by better health and access to health care may allow females to capitalise on the genetic quality afforded by selecting a risk-prone male whilst concurrently buffering the potential costs associated with the risk taker’s lower paternal investment. The risk of contracting COVID-19 did not predict avoidance of risk takers, perhaps because this environmental cue is too novel to have moulded our behavioural preferences

Asian Elephants (Elephas maximus) Discriminate Between Familiar and Unfamiliar Human Visual and Olfactory Cues

Social animals use individual identity cues to form and maintain social relationships with conspecifics. This ability to discriminate between individuals extends to heterospecifics in some social mammals. The aim of this study was to determine if Asian elephants (Elephas maximus) could differentiate between familiar and unfamiliar people using visual, auditory, and olfactory cues independently. Two female Asian elephants at the Perth Zoo were tested with stimuli generated from six humans. Video playbacks, auditory playbacks and pieces of worn shirts were used to present familiar and unfamiliar human stimuli to the elephants using a simultaneous two-choice task. Trunk reach duration and trunk reach frequency were used as measures of the elephants' interest in the stimuli. The elephants’ trunk reach durations revealed a significant difference between familiar and unfamiliar human stimuli using visual cues alone, with significantly more trunk reaching toward familiar human stimuli. No significant difference in trunk reach duration was seen between familiar and unfamiliar human stimuli for auditory or olfactory cues. Trunk reach frequency revealed a significant difference between familiar and unfamiliar human stimuli for visual and olfactory stimuli, with a greater frequency of trunk reaching towards familiar stimuli for both modes. No significant difference in trunk reach frequency was seen between familiar and unfamiliar human stimuli for auditory cues. This is the first study to use video playbacks with any species of elephant and demonstrates a potential new method for cognitive testing in this species. The results suggest that familiar humans may be important to zoo-housed Asian elephants

Dietary Profile of Rhinopithecus bieti and Its Socioecological Implications

To enhance our understanding of dietary adaptations and socioecological correlates in colobines, we conducted a 20-mo study of a wild group of Rhinopithecus bieti (Yunnan snub-nosed monkeys) in the montane Samage Forest. This forest supports a patchwork of evergreen broadleaved, evergreen coniferous, and mixed deciduous broadleaved/coniferous forest assemblages with a total of 80 tree species in 23 families. The most common plant families by basal area are the predominantly evergreen Pinaceae and Fagaceae, comprising 69% of the total tree biomass. Previous work has shown that lichens formed a consistent component in the monkeys’ diet year-round (67%), seasonally complemented with fruits and young leaves. Our study showed that although the majority of the diet was provided by 6 plant genera (Acanthopanax, Sorbus, Acer, Fargesia, Pterocarya, and Cornus), the monkeys fed on 94 plant species and on 150 specific food items. The subjects expressed high selectivity for uncommon angiosperm tree species. The average number of plant species used per month was 16. Dietary diversity varied seasonally, being lowest during the winter and rising dramatically in the spring. The monkeys consumed bamboo shoots in the summer and bamboo leaves throughout the year. The monkeys also foraged on terrestrial herbs and mushrooms, dug up tubers, and consumed the flesh of a mammal (flying squirrel). We also provide a preliminary evaluation of feeding competition in Rhinopithecus bieti and find that the high selectivity for uncommon seasonal plant food items distributed in clumped patches might create the potential for food competition. The finding is corroborated by observations that the subjects occasionally depleted leafy food patches and stayed at a greater distance from neighboring conspecifics while feeding than while resting. Key findings of this work are that Yunnan snub-nosed monkeys have a much more species-rich plant diet than was previously believed and are probably subject to moderate feeding competition

Multilevel Societies in Primates and Other Mammals: Introduction to the Special Issue

# The Author(s) 2012. This article is published with open access at Springerlink.co

Are Hylobates lar Extirpated from China?

The Nangunhe Nature Reserve in Southwest Yunnan (PRC) has long been presumed to be the last stronghold of lar (or white-handed) gibbons (Hylobates lar) in China and the likely last place of occurrence of Hylobates lar yunnanensis. We conducted a comprehensive survey to assess the status of lar gibbons at Nangunhe. We found no visual or auditory evidence of them still residing at the reserve and therefore tentatively conclude that lar gibbons have become extinct in China. It appears that large-scale destruction of primary forests in the 1960s and 1970s brought about an initial decline in their numbers, and subsequent uncontrolled hunting has resulted in their extirpation. The situation for the six Chinese ape taxa is nothing less than disastrous, with 1 taxon assumed to have become extinct during the last few years, 1 taxon not having been confirmed since the 1980s, and 2 species at the very brink of extinction with only tens of individuals remaining in China

Fruiting and flushing phenology in Asian tropical and temperate forests: implications for primate ecology.

In order to understand the ecological adaptations of primates to survive in temperate forests, we need to know the general patterns of plant phenology in temperate and tropical forests. Comparative analyses have been employed to investigate general trends in the seasonality and abundance of fruit and young leaves in tropical and temperate forests. Previous studies have shown that (1) fruit fall biomass in temperate forest is lower than in tropical forest, (2) non-fleshy species, in particular acorns, comprise the majority of the fruit biomass in temperate forest, (3) the duration of the fruiting season is shorter in temperate forest, and (4) the fruiting peak occurs in autumn in most temperate forests. Through our comparative analyses of the fruiting and flushing phenology between Asian temperate and tropical forests, we revealed that (1) fruiting is more annually periodic (the pattern in one year is similar to that seen in the next year) in temperate forest in terms of the number of fruiting species or trees, (2) there is no consistent difference in interannual variations in fruiting between temperate and tropical forests, although some oak-dominated temperate forests exhibit extremely large interannual variations in fruiting, (3) the timing of the flushing peak is predictable (in spring and early summer), and (4) the duration of the flushing season is shorter. The flushing season in temperate forests (17-28 % of that in tropical forests) was quite limited, even compared to the fruiting season (68 %). These results imply that temperate primates need to survive a long period of scarcity of young leaves and fruits, but the timing is predictable. Therefore, a dependence on low-quality foods, such as mature leaves, buds, bark, and lichens, would be indispensable for temperate primates. Due to the high predictability of the timing of fruiting and flushing in temperate forests, fat accumulation during the fruit-abundant period and fat metabolization during the subsequent fruit-scarce period can be an effective strategy to survive the lean period (winter)