Parasites, fossils and geologic history: Historical biogeography of the South American freshwater croakers, Plagioscion spp. (Teleostei, Sciaenidae)

A hypothesis on the historical biogeography of the freshwater croakers, Plagioscion spp. (Teleostei: Sciaenidae), is developed based on data from the phylogeny of their monogenoidean parasites (Platyhelminthes), the geology of South America and the fossil record. Analyses suggest that the common ancestor of Plagioscion spp. colonized freshwater concomitantly with the common ancestor of their parasites, Eurybaliotrema spp. Colonization probably occurred via a marine transgression through western Venezuela that developed about 20 million years ago (Mya). This transgression with its postulated highly variable temporal and spatial salinity conditions most likely represented the facilitating event associated with freshwater colonization. A less likely alternative, that colonization occurred via the Mar del Plata in southern South America, is not supported by the geographical distributions and putative phylogeny of extant species of Plagioscion.