Evidence of lack of gene flow among continental and insular Sheldgeese populations (Chloephaga: Anatidae): taxonomic implications and hope for a seriously threatened species

KOPUCHIAN, CECILIA

Pirenopolis

Congreso; XXII Congreso Brasileiro de Ornitologia; 2016

Sociedad Brasilera de Ornitologia

Species endemic to archipelagos worldwide illustrate the importance of geographic isolation in the process of speciation. The Malvinas/Falkland Islands (MFI) constitute the largest archipelago in the Southern Atlantic, located ~450 kilometers east of Tierra del Fuego (Patagonia). The MFI harbor endemic lineages (including plants, invertebrates and vertebrates) that evolved after ancestral populations became isolated during the Pleistocene glaciations. Various bird species have populations on the continent and the MFI that are not genetically differentiated, suggesting geographic isolation may not be enough to reduce gene flow in highly vagile species, and thus allow diversification. Two species of sheldgeese, Chloephaga picta and Chloephaga rubidiceps, have populations that are co-distributed between the MFI and Patagonia and show opposing demographic trends: while insular populations are increasing in size, continental ones are in sharp decline, due mainly to anthropogenic causes. We used a genomic approach to quantify differentiation among insular and continental populations of both species, and used coalescent-based analyses to model their demographic history. Our results show that the MFI harbor independently evolving lineages of C. picta and C. rubidiceps, which diverged from their continental counterparts during the Pleistocene and have since experienced negligible gene flow. We conclude that the ~450 km that separate the archipelago from the continent are sufficient to isolate populations of these otherwise highly vagile species. This implies that without appropriate conservation measures, the drastic decline of the morphologically, behaviorally and ecologically distinct continental population of C. rubidiceps, to