Climate oscillations may drive the divergence of ancestral species through habitat isolation, species distribution patterns, and the cessation of gene flow. However, traditional ecological niche models lack the consideration for the genetic adaptation of species, thus it’s difficult to understand how climate oscillations affect species divergence by changing their climatic suitability and historical demography. We analyzed the impact of climate change on the divergence of two langur species, François’ langur and White-headed langur, using Maxent, Genotype–Environment Association (GEA) models and genomic data. Our results indicate that 1) Climatic suitability for François’ langur and White-headed langur has separated from the Last Interglacial (LIG, 120,000-140,000 years ago) to the Last Glacial Maximum (LGM); 2) Although the effective population size for both species decreased between the LIG and the LGM, the effective population size of François’ langur increased more quickly than that of White-headed langur from the LGM to the present; 3) Historical patterns of climate change have resulted in periods of expanded and contracted climatic suitability, with each species experiencing periods of interspecific genetic isolation and periods of interspecific genetic exchange; and 4) Human activities and future climate change have contracted the range of François’ langur (in China) and White-headed langur. Climate oscillation, population isolation, and in situ evolution in refugia from the LIG to the LGM appear to have played a critical role in langur speciation and adaptive evolution. Overall, our results demonstrate how climatic oscillations and historical demography drive speciation, providing a new perspective on species divergence and conservation.

Resources critical for successful breeding are typically partition in nature. To increase reproductive fitness, females may associate with males who provide access to high quality resources while mating other males with good or compatible genes. Gibbons have traditionally been described as living in small monogamous groups and the sole resident adult male is assumed to sire all of the group’s offspring. Based on 16 years of field observations and microsatellite analyses, we describe the social system and reproductive strategies of a population of Nomascus concolor in the Wuliang Mountains, China. From 2003 to 2018, each of our three study groups consisted one resident male and two breeding females across 98.4% of observation months. Resident males spent 2.3 - 5.6% time (N = 7 pairs) within 1 m of both females in their group, comparable to monogamous gibbon groups. Weakened bond strength predicted male/female replacement in two groups. However, microsatellite analyses revealed that the rate of extra-group paternity (EGP) was 40.0% (N = 15), considerably greater than reported for monogamous gibbon species (0 - 10%). Females engaged in EGP to increase offspring heterozygosity. Resident males seem unable to monopolize the mating activities of females, floater males had reproductive success (N = 2). Our findings indicate that in crested gibbons the social system is distinct from the breeding system. Our study also highlights again that long-term continuous field work and non-invasive genetic analysis are essential for understanding breeding systems of long-lived mammals.