COS 176-2 - Genetic and demographic consequences of forest fragmentation in black howler monkeys

Background/Question/Methods

Forest loss and fragmentation is one of the most urgent threats to arboreal primate species worldwide. This process creates small, divided populations that occupy forest fragments of varying quality and isolation. One important impact of the loss of connectivity is the restriction of dispersal, which alters patterns of gene flow in the population. Over time, the genetic effects of reduced gene flow, such as a reduction in genetic diversity and increased inbreeding, can contribute to a population’s eventual extirpation. We aimed to evaluate genetic isolation and changes to population demographic structure induced by forest fragmentation in endangered black howler monkeys (Alouatta pigra) inhabiting 32 small (0.2-36 ha), unprotected forest fragments located within 10km of Palenque National Park (PNP) in Chiapas, Mexico (N=407 ind., 3-38 ind./fragment). For genomic analyses, we extracted DNA from individually identified and georeferenced fecal samples collected from 88 adults. We used double-digest restriction site associated DNA sequencing (ddRAD-seq) to generate a single nucleotide polymorphism (SNP) dataset. After quality control, we arrived at a final dataset of 8390 SNPs that we used to analyze the genomic population structure.

Results/Conclusions

We observed genetic clusters that closely corresponded to a single forest fragment, as well as genetic clusters that corresponded to small groups of fragments that clustered together in the landscape. We identified a number of potentially-dispersed individuals, which were genetically assigned to clusters associated with fragments far from their sampling location. Our results suggest that forest fragmentation is inducing genetic isolation at fine geographic scales, with restricted gene flow to and from some forest fragments, although some individuals may still be dispersing successfully across the matrix. Our demographic analyses showed that, overall, the population in forest fragments had significantly fewer adult males than the adjacent population in PNP, which suggests one specific way in which habitat fragmentation may be restricting gene flow: increased male mortality during dispersal. Given the small size of the forest fragments and within-fragment populations, this evidence of restricted movement and gene flow is of conservation concern. We are expanding our investigation into the effects of fragmentation on black howler dispersal and population genetic structure, incorporating a larger dataset of sequenced individuals and landscape information. These analyses will allow us to incorporate genetic information into population viability analyses, and develop optimal intervention strategies.