Effects of Genetic Relatedness and Dispersal Patterns on Gut Microbiota and Parasite Transmission in Proboscis Monkeys



The main objective of this study was to examine the relatedness and dispersal patterns of proboscis monkeys in the Menanggul area of the Lower Kinabatangan Wildlife Sanctuary.

Based on previous observations, serious aggressions in males within reproductive minimum units (harems) and between reproductive and all-male units were rare in the lower Kinabatangan. In addition, there were no (even suspected) infanticide behaviours in proboscis monkeys after taking over the minimum reproductive units by new males and even after adult females were transferred into the unit with a newborn infant. All the evidence strongly indicated that there is a mechanism to reduce the mating competition among male proboscis monkeys. Therefore, it was expected that males in each minimum reproductive unit within the same bands are genetically highly related to each other as males transfer within bands. However, it was also expected that serious aggressions would occur between males from different bands as males do not migrate beyond bands, i.e., males in different bands are unrelated. Within the bands, males in all-male units may also be related to (harem) males in the minimum reproductive units. This may be the reason why serious aggressions are avoided among males within the bands in proboscis monkeys. On the other hand, it is expected that as females transfer to the other units, probably even beyond bands, to avoid their inbreeding, the degree of female relatedness within the minimum reproductive units and within/between bands should be equal to each other and lower than those in males.

In relation to the above expected genetic patterns of proboscis monkeys, we expect that females mainly cause parasite transmission as they frequently transfer among units and even beyond bands. In addition, the similarity of gastrointestinal (GI) microbiome composition will positively correlate with the relatedness of proboscis monkeys. Since males only transfer within bands, they will share similar food items in the same habitat, and thus, higher similarity of GI microbiome composition among males within bands is expected. However, lower similarity is expected between males in different bands. Lastly, the similarity of GI microbiome composition is lower among females than that in males as females frequently transfer to units and bands, i.e. females frequently change their habitats probably with their diets.

  1. Male proboscis monkeys in minimum reproductive units and all-male units within bands show a higher degree of relatedness than those within different bands, as males only transfer between units within bands.
  2. The degree of relatedness of female proboscis monkeys is generally lower than that of males; it is similar within and between minimum reproductive units, even between those in different bands, as females frequently transfer between units and bands.
  3. Parasite transmission is mainly caused by female proboscis monkeys, as females frequently transfer between units and bands.
  4. Gastrointestinal (GI) microbiome composition is similar among males within bands, though such similarity is lower between males with different bands.
  5. The similarity of GI microbiome composition is lower among females than in males, as only females may frequently transfer between units and bands.

The laboratory work for the relatedness analyses was performed at the Wildlife Health, Genetic and Forensic Laboratory by DGFC’s Senior Conservation Geneticist and supervised by DGFC’s Scientific Advisor.

Proboscis monkeys ©Rudi Delvaux
Proboscis monkeys ©Rudi Delvaux