The role of Miocene-Pleistocene environmental change in diversification of the genusHypoclinemusChabanaud, 1928

Abstract

The Neotropical region stands out as one of the most taxonomically diverse areas on the planet, garnering significant attention in the context of marine incursions and their role in shaping this diversity. Among marine-derived taxa, pleuronectiform fishes exhibit distinctive morphological characteristics that have attracted significant scientific interest. However, the biogeography ofHypoclinemus mentalis, initially described asSolea mentalisand subsequently assigned to the genusAchirus, was eventually reclassified into its current monotypic genus due to its limited distribution in freshwater environments, in contrast to the species ofAchirus. The broad distribution of a single species across multiple South American river basins positionsH. mentalisas an ideal candidate for biogeographic studies within South America, with an emphasis on the detection of cryptic lineages associated with major drainage basins. In our study, we employed mitochondrial and nuclear markers to investigate the potential existence of such lineages within the broader context of a molecular phylogeny that encompasses all valid genera in the flatfish family Achiridae. Our findings reveal thatHypoclinemuscomprises seven operational taxonomic units (OTUs), as deduced from specimens collected across the majority of its documented range. Furthermore, our phylogeographic analyses support the hypothesis that colonization of freshwater habitats occurred through connections between the Caribbean Sea and Lake Pebas approximately 21.28 million years ago. Moreover, we observed that differentiation of lineages within theHypoclinemusgenus was significantly influenced by pronounced sea level fluctuations during the Plio-Pleistocene epoch, underscoring the impact of glaciations and interglacial periods on the biogeographic patterns.