The Genetic Status of the Critically Endangered Hainan Gibbon (Nomascus hainanus): A Species Moving Toward Extinction

Abstract

The Hainan gibbon (Nomascus hainanus), once widespread across Hainan, China, is now found only in the Bawangling National Nature Reserve. With a remaining population size of 33 individuals, it is the world's rarest primate. Habitat loss and fragmentation are the primary drivers of Hainan gibbon population decline. In this study, we integrated data based on field investigations and genotype analyses of 10 microsatellite loci (from fecal samples) to assess genetic diversity in this Critically Endangered primate species. We found that the genetic diversity of the Hainan gibbon is extremely low, with 7 of 8 microsatellite loci exhibiting decreased diversity. Additional molecular analyses are consistent with field observations indicating that individuals in groups A, B, and C are closely related, the female-male sex ratios of the offspring deviates significantly from 1:1, and the world's remaining Hainan gibbon population is expected to experience continued high levels of inbreeding in the future. Given extensive habitat loss (99.9% of its natural range has been deforested) and fragmentation, this rarest ape species faces impending extinction unless corrective measures are implemented immediately.

Keywords: Hainan gibbon; conservation; critically endangered; genetic status; population size.

FIGURE 1

Distribution of the five remaining groups of Hainan gibbons (Group E was discovered in June 2020; the survey of this study does not include Group E).

FIGURE 2

The size and composition four wild Hainan gibbon groups. AM represents an adult male, AF represents an adult female, S-A represents a subadult, JM represents a juvenile, I represents an infant, and (U) represents an adult, subadult, juvenile, or infant of unknown sex. Infants are 0–24 months of age, juveniles are >2–7 years of age, subadults are >7–9 years of age, and adults are >9 years of age.

FIGURE 3

Sex identification electrophoresis test results. Males have 2–3 bands, females have only 1 band, and numbers 1–8 are the PCR products of Scheme A. The blank control group does not have any bands, the target band is bright, and the background is clean; Numbers 9–16 are the PCR products of Scheme B. The blank control group has no bands, the target bands have a clean background, and the bands are fuzzy; Numbers 17–25 are the PCR products of Scheme C. The blank control group has no bands, the target bands are bright, and the background is clean, but some samples have nonspecific amplification.

FIGURE 4

Individual identification system ability curve.

FIGURE 5

Genetic maps of 3 Hainan gibbon groups.

FIGURE 6

Distribution of allele frequencies for the historical and current populations across 8 loci.

FIGURE 7

Kinship diagram of individuals in Groups A, B, and C. Based on these results, both males and females transfer between established groups, and given the existence of new groups (D and E), individuals periodically form new groups.