A Hotspot Atop: Rivers of the Guyana Highlands Hold High Diversity of Endemic Pencil Catfish

Abstract

AimThe Pakaraima Mountains are an ancient mountain range along the borders of Guyana, Brazil, and Venezuela. The high plateau is drained by multiple river systems in all directions. Although hypotheses have been presented for the biogeographic relationships of lowland rivers, the interconnectivity of rivers on the top of the plateau is unknown. With multiple complex rivers in a small, upland area we predicted a high level of endemism for stream fishes and complex biogeographic relationships. We explore this with the incredibly diverse pencil catfish genus Trichomycterus. Only two species are known from the region. In this study, we 1) confirm the discovery of multiple endemic Trichomycterus species in the region, 2) determine the phylogenetic placement of our samples to posit biogeographical scenarios, and 3) provide clarification for the identification of T. guianensis based on morphology.\n\nLocationPakaraima Mountains, a part of the Guiana Shield in Guyana, South America\n\nTaxonPencil catfish genus Trichomycterus\n\nMethodsUsing collections from recent expeditions to the Pakaraima Mountains of Guyana, we amplified three mitochondrial (16S, COI, and cytb) and two nuclear markers (myh6 and RAG2). We constructed individual gene trees as well as a concatenated tree to determine the placement of these taxa within the Trichomycterus of the Trans-andean/Amazonian clade.\n\nResultsOur results identify six unique lineages in the highlands of Guyana. Only two species, Trichomycterus guianensis and T. conradi, were previously known to science.\n\nMain ConclusionsThe Pakaraima Mountains of South America are a region of high endemism, as demonstrated here in Trichomycterus catfishes. We find two species occupying multiple basins, suggesting that Pakaraima streams either maintain or had some degree of recent connectivity. We identify six endemic lineages of Trichomycterus from the highlands of the Pakaraima Mountains. The upper portions of the study rivers have been connected either through surface flow or by stream capture. Both processes have occurred on multiple time scales and are independent of the patterns seen in the lowlands.