Habitat fragmentation and genetic variation in the endangered black lion tamarin (Leontopithecus chyrsopygus)
Fragmentation threatens biodiversity globally. The black lion tamarin (Leontopithecus chrysophagus) is an IUCN endangered species, and is considered to be the rarest New World monkey. The objective in this study was to examine genetic variation in a critical immune response gene, DARC (Duffy antigen receptor for chemokines), which encodes DARC, a promiscuous chemokine receptor, a blood group antigen and a binding site for the malarial parasites Plasmodium vivax and P. knowlesi. Variation in DARC may play particularly significant roles in innate immunity, immunotolerance and pathogen entry in callitrichines, such as the black lion tamarin, due to their unique life histories. We compared the exonic sequence of DARC across 19 black lion tamarins from four forest fragments, as well as to a subset of non-human Haplorhine primates and Homo sapiens.
We found no variation in DARC across the black lion tamarins studied. However, we did find significant differences between black lion tamarins and other primates, including humans. Three amino acid variants (D21N, F22L, V25L) occured in residues critical for P. vivax and P. knowlesi binding. F22 was subject to both positive selection pressure and fixation in NWMs, suggesting a selective sweep and role as an adaptive barrier to Plasmodium entry. Lion tamarins also differed from humans at the FyA/B antigen-binding sites 42 and 44, as well as the putative destabilizing residues A61, T68, A187 and L215. In contrast, the vital DARC residues for chemokine binding were conserved across Haplorhine primates. Our results agree with previous findings, that the DARC gene experiences two opposing selection forces in haplorhines: 1) positive selection on the Plasmodium binding site, and 2) purifying selection on the chemokine receptor. The putative Plasmodium barrier may become advantageous to Black Lion Tamarins should climate change predictions of malaria expansion hold true, while changes in FyA/B antigen-binding sites could interrupt the Fy antigen system and facilitate tolerance during fetal anastomosis in callitrichines.