Hydrological link between the Amazon River Basin and the eastern Guiana Shield on the Neotropical ichthyofauna

Abstract

The seasonal inundation of the Rupununi savannas in south central Guyana allows for potential faunal exchange between the Takutu and Rupununi Rivers and ultimately between the Essequibo and Amazon Rivers. This hydrological connection unites two distinct regions in South America, the Amazon River basin to the drainages of the eastern Guiana Shield. Significant fish community differences on either side of the Rupununi portal suggest the importance of this feature on fish distributions. Therefore, in order to further investigate the influence of the Rupununi portal on fish distributions, I evaluated gene flow of five species found across the portal. This study incorporated three molecular markers: two mitochondrial genes and one nuclear gene. Population genetics of the five species varied, suggesting that the Rupununi portal is acting as a barrier to dispersal for some and a conduit for others. These patterns were based primarily on their ecology. In addition to population genetics of species across the portal, assuming a molecular clock I was able to estimate the timing of the final breakup of the proto-Berbice, thus forming the Rupununi portal. This study highlights the significance of the Rupununi portal in uniting the most species rich river in the world to a region of historical geological complexity and its role in shaping fish distributions of the Neotropical ichthyofauna.