How geographic boundaries interact with primate locomotion and ecology to fragment populations, form new species, and lead to their extinction remains a fundamental question for biological anthropologists. Little effort has been made, however, to ascertain precisely how subtle geographic variation actually modifies the underlying population genetic relationships of primates in a changing environment. As human-induced environmental degradation continues to isolate and fragment dwindling populations of primates, it has become critical to understand how innate biological factors influence the ability of primates to disperse through and exchange genes within these variable environments.
Black crested gibbons (Nomascus concolor) and Phayre's leaf monkeys (Trachypithecus phayrei) have overlapping habitats in many parts of Yunnan, China, but it is unclear how their biological differences (in ecology, locomotion, etc.) affect their abilities to overcome the geographic barriers imposed by both a naturally diverse landscape and one actively modified by humans. Research conducted by doctoral student Joseph Orkin (Washington University in St. Louis), under the supervision of Dr. Richard Smith, examines how the same geographic boundaries (mountains, forest structure, and rivers) affect the capability of these distinct, endangered primates to disperse and exchange genes. By comparing paired populations of two declining species that have been simultaneously fragmented within the same variable habitat, the research tests the hypothesis that these differences in locomotion and ecology are affecting both the evolution and survival of gibbons and leaf monkeys. The research provides a robust, new understanding of the interacting causes of population fragmentation, and yields real conservation impacts. By forging new, long-term collaborative ties between the American and Chinese primatological communities, it also provides a mutual sharing of knowledge and experience to help maintain biodiversity in a critical region.
It has long been assumed that geographic boundaries like forest structure, rivers, and mountains can lead to the fragmentation and isolation of primate populations. However, very little is known about how these barriers are affected by primate locomotion, social structure, and life history. All of these factors interact to subdivide free-ranging populations of primates, which can lead to species formation, fragmentation, and extinction. However, little effort has been made to ascertain precisely how this small-scale geographic variation actually modifies population genetic relationships in a changing environment. As humans continue to alter the landscape in and around primate habitat, primates continue to become restricted in fragmented dwindling populations. It has become critical to understand how primates' innate biology and behavior influences their ability dispersal through degraded forests. Western black crested gibbons (Nomascus concolor) and Phayre's leaf monkeys (Trachypithecus phayrei) are both endangered primates located in sky-island habitats in southwestern China. These primates have been isolated by recent deforestation into highly variable mountaintop forests. At altitudes above 2,700 meters, the forest degrades into thickets of rhododendrons through which we hypothesize gibbons will be unable to disperse. If this is so, we expect to identify stronger than expected population genetic subdivision on either side of these degraded forest boundaries. We collected 202 presumed primate scat samples from free-ranging groups of primates in four regions of southwest China (Yunnan Province) for landscape genetic analysis. Because these primates are not habituated to human observers, we collected scat samples with the use of a scat detection dog trained in China. We successfully amplified primate DNA from 140 of these samples. We generated 15 genetic markers (polymorphic microsatellites) to identify distinct individuals and produce multilocus genotypes for each individual. By assessing how related individual primates are to each other on opposite sites of a potential boundary, we can determine if primates are unable to cross the geographic boundary (e.g. areas of degraded forest) to reproduce. Our results indicate that gene flow in gibbons is being restricted both by high-altitude rhododendron thickets and recent human deforestation. Substantial research in biological anthropology hinges on the assumption that primates with different locomotor adaptations will have different abilities at moving through degraded and variable habitats. Gibbons are among the most arboreally dependent primates, using a distinct arm-swinging, suspensory type of locomotion. Prior to this research, nothing was known about how habitat structure affects the population genetics of these unique primates. Our research is the first to describe how landscape affects the population genetic structure of gibbons. This fact provides profound evidence to support the notion that not all primates will be able to disperse effectively through changing, degraded habitats. It also yields some of the first direct genetic support for the potential adaptive benefit of a changing primate body plan that allows more efficient locomotion to overcome degraded habitats. Furthermore, our results will be integrated into an informed conservation management plan with the relevant local authorities.
