Evidence of male-biased dispersal in the endangered Sichuan snub-nosed monkey (Rhinopithexus roxellana)

Drone Observation for the Quantitative Study of Complex Multilevel Societies

Unmanned aerial vehicles (drones) have recently been used in various behavioral ecology studies. However, their application has been limited to single groups, and most studies have not implemented individual identification. A multilevel society refers to a social structure in which small stable "core units" gather and make a larger, multiple-unit group. Here, we introduce recent applications of drone technology and individual identification to complex social structures involving multiple groups, such as multilevel societies. Drones made it possible to obtain the identification, accurate positioning, or movement of more than a hundred individuals in a multilevel social group. In addition, in multilevel social groups, drones facilitate the observation of heterogeneous spatial positioning patterns and mechanisms of behavioral propagation, which are different from those in a single-level group. Such findings may contribute to the quantitative definition and assessment of multilevel societies and enhance our understanding of mechanisms of multiple group aggregation. The application of drones to various species may resolve various questions related to multilevel societies.

Dispersal patterns in Yunnan snub-nosed monkeys

Sex-biased dispersal is common in group-living animals. Due to differences in local demographic and environmental factors, sex-biased dispersal presents many irregular patterns. In this study, a habituated, individually identified Yunnan snub-nosed monkey Rhinopithecus bieti group was observed over 9 years; 192 dispersal events, including 97 male dispersal events (25 natal dispersal and 72 secondary dispersal) and 95 female dispersal events (34 natal dispersal and 61 secondary dispersal) were observed. Males and females showed different dispersal paths, dispersal ages, and dispersal patterns. Females had 2 dispersal paths, whereas males had 4 paths. In terms of age of dispersal, the male age of natal dispersal was younger than for females. Males prefer single dispersal, whereas females prefer parallel dispersal. Our study indicates that the dispersal pattern of R. bieti should be classified as a bisexual dispersal pattern. The differences in dispersal path, average age at dispersal, and dispersal path pattern indicate that Yunnan snub-nosed monkeys may still retain a loose matrilineal social system.

Genetic Structure and Evolutionary History of Rhinopithecus roxellana in Qinling Mountains, Central China

The Qinling mountainous region is one of the world's biodiversity hotspots and provides refuges for many endangered endemic animals. The golden snub-nosed monkeys (Rhinopithecus roxellana) are considered as a flagship species in this area. Here, we depicted the genetic structure and evolutionary history via microsatellite markers and combination with the ecological niche models (ENMs) to elucidate the intraspecific divergent and the impacts of the population demography on our focal species. Our results revealed three distinct subpopulations of R. roxellana and also uncovered asymmetric historical and symmetric contemporary gene flow that existed. Our evolutionary dynamics analyses based on diyabc suggested that the intraspecific divergence accompanied with effective population sizes changes. The ENM result implied that the distribution range of this species experienced expansion during the last glacial maximum (LGM). Our results highlighted that geological factors could contribute to the high genetic differentiation within the R. roxellana in the Qinling Mountains. We also provided a new insight into conservation management plans with endangered species in this region.

Kin bias and male pair-bond status shape male-male relationships in a multilevel primate society

Abstract

Male-male social relationships in group-living mammals vary from fierce competition to the formation of opportunistic coalitions or the development of long-lasting bonds. We investigated male-male relationships in Guinea baboons (Papio papio), a species characterized by male-male tolerance and affiliation. Guinea baboons live in a multi-level society, with units of one reproductively active “primary” male, 1–6 females, and offspring at the core level. Together with “bachelor” males, several units form a party, and 2–3 parties constitute a gang. We aimed to clarify to which degree male relationship patterns varied with relatedness and pair-bond status, i.e., whether males had primary or bachelor status. Data were collected from 24 males in two parties of Guinea baboons near Simenti in the Niokolo-Koba National Park in Senegal. Males maintained differentiated and equitable affiliative relationships (“strong bonds”) with other males that were stable over a 4-year period, irrespective of their pair-bond status. Remarkably, most bachelor males maintained strong bonds with multiple primary males, indicating that bachelor males play an important role in the cohesion of the parties. A clear male dominance hierarchy could not be established due to the high degree of uncertainty in individual rank scores, yet bachelor males were more likely to be found at the low end of the dominance hierarchy. Average relatedness was significantly higher between strongly bonded males, suggesting that kin biases contribute to the social preferences of males. Long-term data will be needed to test how male bonds affect male tenure and ultimately reproductive success.

Significance statement

Males living in social groups may employ different strategies to increase their reproductive success, from fierce fighting to opportunistic alliance formation or the development of long-term bonds. To shed light on the factors that shape male strategies, we investigated male-male social relationships in the multilevel society of Guinea baboons (Papio papio) where “primary” males are associated with a small number of females and their offspring in “units” while other males are “bachelors.” Strong bonds occurred among and between primary and bachelor males and strongly bonded males were, on average, more closely related. Bachelor males typically had multiple bond partners and thus play an important role in the fabric of Guinea baboon societies. Across primate species, neither dispersal patterns nor social organization clearly map onto the presence of strong bonds in males, suggesting multiple routes to the evolution of male bonds.

Genetic Diversity, Inbreeding Level, and Genetic Load in Endangered Snub-Nosed Monkeys (Rhinopithecus)

The snub-nosed monkey genus (Rhinopithecus) comprises five closely related species (R. avunculus, R. bieti, R. brelichi, R. roxellana, and R. strykeri). All are among the world's rarest and most endangered primates. However, the genomic impact associated with their population decline remains unknown. We analyzed population genomic data of all five snub-nosed monkey species to assess their genetic diversity, inbreeding level, and genetic load. For R. roxellana, R. bieti, and R. strykeri, population size is positively correlated with genetic diversity and negatively correlated with levels of inbreeding. Other species, however, which possess small population sizes, such as R. brelichi and R. avunculus, show high levels of genetic diversity and low levels of genomic inbreeding. Similarly, in the three populations of R. roxellana, the Shennongjia population, which possesses the lowest population size, displays a higher level of genetic diversity and lower level of genomic inbreeding. These findings suggest that although R. brelichi and R. avunculus and the Shennongjia population might be at risk, it possess significant genetic diversity and could thus help strengthen their long-term survival potential. Intriguingly, R. roxellana with large population size possess high genetic diversity and low level of genetic load, but they show the highest recent inbreeding level compared with the other snub-nosed monkeys. This suggests that, despite its large population size, R. roxellana has likely been experiencing recent inbreeding, which has not yet affected its mutational load and fitness. Analyses of homozygous-derived deleterious mutations identified in all snub-nosed monkey species indicate that these mutations are affecting immune, especially in smaller population sizes, indicating that the long-term consequences of inbreeding may be resulting in an overall reduction of immune capability in the snub-nosed monkeys, which could provide a dramatic effect on their long-term survival prospects. Altogether, our study provides valuable information concerning the genomic impact of population decline of the snub-nosed monkeys. We revealed multiple counterintuitive and unexpected patterns of genetic diversity in small and large population, which will be essential for conservation management of these endangered species.

Bachelor groups in primate multilevel society facilitate gene flow across fragmented habitats

In the face of ongoing habitat fragmentation, many primate species have experienced reduced gene flow resulting in a reduction of genetic diversity, population bottlenecks, and inbreeding depression, including golden snub-nosed monkeys Rhinopithecus roxellana. Golden snub-nosed monkeys live in a multilevel society composed of several 1 male harem units that aggregate to form a cohesive breeding band, which is followed by one or more bachelor groups composed of juvenile, subadult, and adult male members. In this research, we examine the continuous landscape resistance surface, the genetic diversity and patterns of gene flow among 4 isolated breeding bands and 1 all-male band in the Qinling Mountains, China. Landscape surface modeling suggested that human activities and ecological factors severely limit the movement of individuals among breeding bands. Although these conditions are expected to result in reduced gene flow, reduced genetic diversity, and an increased opportunity for a genetic bottleneck, based on population genetic analyses of 13 microsatellite loci from 188 individuals inhabiting 4 isolated breeding bands and 1 all-male band, we found high levels of genetic diversity but low levels of genetic divergence, as well as high rates of gene flow between males residing in the all-male band and each of the 4 breeding bands. Our results indicate that the movement of bachelor males across the landscape, along with their association with several different breeding bands, appears to provide a mechanism for promoting gene flows and maintaining genetic diversity that may counteract the otherwise isolating effects of habitat fragmentation.

Reproductive strategy of bachelors in a snub-nosed monkey (Rhinopithecus bieti) all-male unit

Snub-nosed monkeys exhibit a rare multilevel social system composed of several one-male units (OMU) and at least one all-male unit (AMU). The AMU comprises males who are blocked from access to females by resident males in the OMUs, and how these satellite males achieve reproductive success is still unclear. To investigate their reproductive strategies, we focused on the AMU in a band of provisioned black-and-white snub-nosed monkeys (Rhinopithecus bieti) in Yunnan, China. Behaviors that AMU males use to gain access to females (i.e. immigration, male takeover, and sexual interaction with females) were recorded and compared with resident OMU males to explore how AMU bachelors achieve reproductive success when they are denied stable access to females. We found that in response to solicitation from females, adult and sub-adult members of the AMU responded more actively than resident males, and the bachelors actively initiated mating with females when the latter's resident male was temporarily absent. These mating opportunities mostly coincided with the peak mating season in OMUs, and probably allowed bachelors to sire some offspring. We also found that for some AMU adults, taking over an OMU is the main strategy used to gain stable access to females, and these males repeatedly migrate between bands. AMU members therefore show multiple strategies that allow them to gain some degree of reproductive success.

The Origin and Population History of the Endangered Golden Snub-Nosed Monkey (Rhinopithecus roxellana)

The origin and population history of the endangered golden snub-nosed monkey (Rhinopithecus roxellana) remain largely unavailable and/or controversial. We here integrate analyses of multiple genomic markers, including mitochondrial (mt) genomes, Y-chromosomes, and autosomes of 54 golden monkey individuals from all three geographic populations (SG, QL, and SNJ). Our results reveal contrasting population structures. Mt analyses suggest a division of golden monkeys into five lineages: one in SNJ, two in SG, and two in QL. One of the SG lineages (a mixed SG/QL lineage) is basal to all other lineages. In contrast, autosomal analyses place SNJ as the most basal lineage and identify one QL and three SG lineages. Notably, Y-chromosome analyses bear features similar to mt analyses in placing the SG/QL-mixed lineage as the first diverging lineage and dividing SG into two lineages, while resembling autosomal analyses in identifying one QL lineage. We further find bidirectional gene flow among all three populations at autosomal loci, while asymmetric gene flow is suggested at mt genomes and Y-chromosomes. We propose that different population structures and gene flow scenarios are the result of sex-linked differences in the dispersal pattern of R. roxellana. Moreover, our demographic simulation analyses support an origin hypothesis suggesting that the ancestral R. roxellana population was once widespread and then divided into SNJ and non-SNJ (SG and QL) populations. This differs from previous mt-based "mono-origin (SG is the source population)" and "multiorigin (SG is a fusion of QL and SNJ)" hypotheses. We provide a detailed and refined scenario for the origin and population history of this endangered primate species, which has a broader significance for Chinese biogeography. In addition, this study highlights the importance to investigate multiple genomic markers with different modes of inheritance to trace the complete evolutionary history of a species, especially for those exhibiting differential or mixed patterns of sex dispersal.

Identifying refugia and corridors under climate change conditions for the Sichuan snub-nosed monkey (Rhinopithecus roxellana) in Hubei Province, China

Using a case study of an isolated management unit of Sichuan snub-nosed monkey (Rhinopithecus roxellana), we assess the extent that climate change will impact the species' habitat distribution in the current period and projected into the 2050s. We identify refugia that could maintain the population under climate change and determine dispersal paths for movement of the population to future suitable habitats. Hubei Province, China. We identified climate refugia and potential movements by integrating bioclimatic models with circuit theory and least-cost model for the current period (1960-1990) and the 2050s (2041-2060). We coupled a maximum entropy algorithm to predict suitable habitat for the current and projected future periods. Suitable habitat areas that were identified during both time periods and that also satisfied home range and dispersal distance conditions were delineated as refugia. We mapped potential movements measured as current flow and linked current and future habitats using least-cost corridors. Our results indicate up to 1,119 km2 of currently suitable habitat within the study range. Based on our projections, a habitat loss of 67.2% due to climate change may occur by the 2050s, resulting in a reduced suitable habitat area of 406 km2 and very little new habitat. The refugia areas amounted to 286 km2 and were located in Shennongjia National Park and Badong Natural Reserve. Several connecting corridors between the current and future habitats, which are important for potential movements, were identified. Our assessment of the species predicted a trajectory of habitat loss following anticipated future climate change. We believe conservation efforts should focus on refugia and corridors when planning for future species management. This study will assist conservationists in determining high-priority regions for effective maintenance of the endangered population under climate change and will encourage increased habitat connectivity.

Dispersal and female philopatry in a long-term, stable, polygynous gibbon population: Evidence from 16 years field observation and genetics

Gibbons are generally reported to live in small socially monogamous family groups in which both sexes disperse when they reach maturity. For the first time, we documented the dispersal pattern in a population of gibbons living in stable polygynous groups (Nomascus concolor) integrating 16 years' field observation and genetic information from fecal DNA. All subadult males except for one dispersed at 9.8 ± 1.4 years of age (range: 8-12, N = 10). The last male remained in his natal group and obtained the breeding position at age 11 by evicting the original dominant male. Females reached sexual maturity (as evidenced by the change in body color from black to yellow) at 8 years (N = 4). Three of them dispersed and one obtained a position as a breeding female and bred in her natal group. We also observed one female returning to her natal group with her infant after her presumed father was taken over by a neighboring male. We identified only three mtDNA haplotypes from 22 individuals at Dazhaizi. Individuals in one group shared the same haplotype, with only one exception. Genetic results showed that the two breeding females were mother-daughter pairs in all three study groups at the end of this study, implying some degree of female philopatry. We argue that in the case of black crested gibbons, dispersal decisions appear to represent highly opportunistic events in response to reproductive opportunities in their natal and neighboring groups.

Fecal bacterial diversity of wild Sichuan snub-nosed monkeys (Rhinopithecus roxellana)

The gastrointestinal tract of primates harbors a complex microbial community, playing an essential role in the degradation of otherwise indigestible structural carbohydrates. The phylogenetic and functional diversity of the bacterial community in the feces as a surrogate for the gastrointestinal tract of wild Sichuan snub-nosed monkeys (Rhinopithecus roxellana, N = 6) was characterized based on sequence analysis of 16S rRNA genes. A sex comparison was conducted, with a prior hypothesis that the abundances of the bacterial taxa and/or functional categories associated with energy and nutrient metabolism would be higher in adult females (N = 3) due to the higher reproductive costs compared to adult males (N = 3). Ten phyla were identified in all samples, among which Bacteroidetes and Firmicutes were the predominant. Included in the above two phyla, the members of Prevotellaceae (Prevotella in particular) and Ruminococcaceae were highly abundant, which are common bacteria in the gastrointestinal tract of primates and can degrade various structural carbohydrates such as cellulose, hemicellulose, and pectin. This functionality was in line with the high abundances of the metagenomes associated with carbohydrate metabolism. Consistent with our hypothesis, the abundances of the metagenomes associated with energy metabolism, folding/sorting and degradation, glycan biosynthesis and metabolism, and metabolism of amino acids were higher in adult females relative to adult males. Sex differences were also detected in the bacterial community structure, although no sex differences in the proportions of any bacterial taxa were found likely due to the small sample size. These results suggested that gastrointestinal bacterial communities may aid adult females in increasing energy and nutrition utilization efficiencies compared to adult males. Fecal bacterial communities were found to be more similar between individuals in adult females than in adult males. Our study presented the first examination of the fecal bacterial diversity of a little-studied, endangered foregut fermenter.

Genetic assessment of an isolated endemic Samango monkey (Cercopithecus albogularis labiatus) population in the Amathole Mountains, Eastern Cape Province, South Africa

The endemic Samango monkey subspecies (Cercopithecus albogularis labiatus) inhabits small discontinuous Afromontane forest patches in the Eastern Cape, KwaZulu-Natal midlands and southern Mpumalanga Provinces in South Africa. The subspecies is affected by restricted migration between forest patches which may impact on gene flow resulting in inbreeding and possible localized extinction. Current consensus, based on habitat quality, is that C. a. labiatus can be considered as endangered as the small forest patches they inhabit may not be large enough to sustain them. The aim of this study was to conduct a molecular genetic investigation to determine if the observed isolation has affected the genetic variability of the subspecies. A total of 65 Samango monkeys (including juveniles, subadults and adults) were sampled from two localities within the Hogsback area in the Amathole Mountains. Nuclear and mitochondrial DNA variation was assessed using 17 microsatellite markers and by sequencing the hypervariable 1 region (HVR1). Microsatellite data generated was used to determine population structure, genetic diversity and the extent of inbreeding. Sequences of the HVR1 were used to infer individual origins, haplotype sharing and haplotype diversity. No negative genetic factors associated with isolation such as inbreeding were detected in the two groups and gene flow between groups can be regarded as fairly high primarily as a result of male migration. This was in contrast to the low nuclear genetic diversity observed (H _o = 0.45). A further reduction in heterozygosity may lead to inbreeding and reduced offspring fitness. Translocations and establishment of habitat corridors between forest patches are some of the recommendations that have emerged from this study which will increase long-term population viability of the subspecies.

Male Dispersal Pattern in Golden Snub-nosed Monkey (Rhinopithecus roxellana) in Qinling Mountains and its Conservation Implication

Golden snub-nosed monkey (Rhinopithecus roxellana) is one of the most endangered primate species found in China, exhibiting multilevel society consisting of several one-male-females together with their offspring units (OMU), and all-male units (AMU). Female dispersal patterns of the species within herd have been well documented, whereas those of the males within or between herds are still poorly understood. Our results based a long-term observation indicate that more than half of sub-adult males, and half of the deposed males that stayed a short period in OMU disperse between herds, three of them established their own OMU in new herd after the dispersal. Smaller number of the sub-adult and adult males, compared with adult females, stayed in natal herd, implying sub-adult males started dispersing and male-biased dispersal occurred between herds. High frequencies of resident males were wounded as their OUMs were taken over, and resident males co-operation defend bachelor males were found. Mating competition among males within the herd may have contributed to the scenarios of male-biased dispersal. The results also suggest that maintaining connection between isolated herds and establishing the corridors among the fragmented habitats for the species will greatly benefit increasing its gene flow and promoting conservation status.

Population structure of the golden snub-nosed monkey Rhinopithecus roxellana in the Qinling Mountains, central China

Environmental barriers and habitat fragmentation can restrict gene flow, leading to genetic divergence among animal populations. The golden snub-nosed monkey, Rhinopithecus roxellana, is endemic to China, and ranges across 4 provinces. However, over the past 40 years its populations have become fragmented. We investigated the genetic diversity, demographic history and population structure of R. roxellana in 5 reserves in one of its strongholds, the Qinling Mountain forests of Shaanxi. We collected genetic material from 11 monkey bands (a group of individuals containing multiple 1-male units) with a total of 428 samples genotyped at 20 microsatellite loci. Allelic richness and heterozygosity suggested a relatively high level of intra-band genetic diversity. We found no evidence of any genetic bottleneck in these R. roxellana populations. AMOVA and Bayesian cluster analysis revealed that R. roxellana in the 5 reserves are highly structured and form at least 3 distinct subpopulations. These subpopulations concur with major topographical features in the study area, such as mountain ridges, suggesting that dispersal of R. roxellana may be restricted by geographical barriers.

An evaluation of hair-snaring devices for small-bodied carnivores in southwest China

Human population growth is a major threat to the biodiversity of mammals in China. Rapid development of infrastructure, pollution, and poor enforcement of environmental laws in China have altered the landscape and accelerated the extinction rates of mammals. To maintain biodiversity and conserve the mammals of China, it is essential to develop monitoring protocols for species of concern that are efficient, cost-effective, and current. It is now common practice for ecologists to survey mammals of interest using noninvasive sampling methods. These sampling techniques are affordable, require no handling of the target animals, and generally yield large samples. In China, such sampling methods have rarely been used and evaluated. For this study, we recorded the behavior of masked palm civets ( Paguma larvata ) and Siberian weasels ( Mustela sibirica ) to determine their relative preference for using different hair-snaring devices and evaluated the effectiveness of each device at collecting hair. Our goal was to determine which genetic sampling method(s) should be used to study masked palm civets and Siberian weasels in the future in Southwest China. In March–June of 2014, we monitored 13 hair-snare stations throughout the Main Valley of Laohegou Nature Reserve, Sichuan Province, China. Genetic analysis revealed that we collected 373 hair samples from civets and 47 hair samples from weasels over 104 and 26 sessions, respectively. Both civets and weasels seemed to prefer lure sticks to ground cubbies; however, the latter were more effective at collecting civet hair. Although glue sheets from lure sticks collected large samples of guard hair (> 10), no device in its current design was consistently effective at collecting weasel hair. We suggest researchers in Southwest China use ground cubbies as described in this study to collect hair from masked palm civets and test other cubby designs (e.g., longer gun brushes or smaller in size) for collecting hair from Siberian weasels.

人口增长是中国哺乳动物多样性危机的主要根源之一。在中国，基础建设的快速发展、环境污染，加之环境执法力度不足造成了哺乳动物的栖息地的退化，加速了动物的灭绝速率。为了维持生物多样性水平和保护中国的哺乳动物，有必要针对受关注的物种开发有效、低成本且通用的监测方法。现在，非损伤性取样方法正被生态学家普遍应用于哺乳动物的调查中。这些调查技术在成本上易于接受，不需要接触目标动物，并且通常可以得到大量可靠的样本。在中国，非损伤性取样方法的应用和评估还较少。本研究中，我们在四川省老河沟自然保护区评估了花面狸和黄鼬对毛发陷阱的访问偏好及陷阱收集动物毛发的有效性；目标是选出有效地遗传取样方法用于将来对花面狸和黄鼬的研究。从2014年3月到6月，我们在保护区主要山谷内设置了13个毛发陷阱站，在收集野生动物的毛发同时使用红外相机记录动物访问陷阱站时的行为。我们发现，相比于设置在地面的小室陷阱，花面狸和黄鼬都更喜欢访问直立的木桩陷阱，但是，小室陷阱能够更有效地收集花面狸的毛发。尽管固定有粘性薄片的木桩 陷阱能够少量收集带有直针毛的毛发（>10根）,但是我们评估的毛发陷阱都不能有效地收集黄鼬的 毛发。根据研究，我们建议研究人员在中国西南可以应用固定有枪刷的小室陷阱（如本研究中所评估的）收集花面狸的毛发，而用更长的枪刷，或者更小的小室陷阱，并固定粘性薄片收集黄鼬的毛发。

Fine-scale genetic assessment of sex-specific dispersal patterns in a multilevel primate society

Like humans, hamadryas baboons (Papio hamadryas) are unusual among primates in having a multilevel social system and stable pair bonds, and are thus a useful model for the evolution of human sociality. While the kinship structure and sex-biased dispersal patterns that underlie human social organization have been extensively elucidated, the impact of these factors on the social system of hamadryas baboons is currently unclear. Here we use genetic analysis of individuals to elucidate the patterns of male and female dispersal across multiple levels of society in a wild population of hamadryas baboons. We characterized 244 members of five hamadryas bands at Filoha, Ethiopia by genotyping one Y-linked and 23 autosomal microsatellite loci and sequencing part of the mitochondrial hypervariable control region I. We found both male and female dispersal to be limited at the level of the band, with more movement of females than males among bands. By integrating long-term behavioral data for Band 1, we also found evidence for male and female philopatry at the clan level. We speculate that male philopatry at the clan level and female dispersal across one-male units and clans may enable both kin-based cooperation among males and the maintenance of kin bonds among females after dispersal. This would mean that, as in humans, kin bonds within both sexes are a core feature of the hamadryas social system, thus contributing to our understanding of the evolution of social organization in humans.