Morphological variation of the Caloneis schumanniana species complex (Bacillariophyceae) from different environmental conditions in North American streams

The aim of the present study is to test by molecular DNA data a hypothesis concerned to speciation by allopatry occurring in Mimagoniates microlepis, associated to the Serra do Mar mountain chain (Atlantic Rain Forest hotspot) in Southern Brazil. Overall genetic diversity and mean genetic distances were high, demonstrating both good conservation status and genetic differentiation. Neighbor-Joining (NJ) and parsimony analyses, together with population genetic parameters (Φ_ST, N_m, G_ST, and AMOVA), identified two main vicariant genetic/evolutionary stocks dividing the upper Iguaçu River samples from those of the coastal plains. Other well-supported intrinsic monophyletic clades were also identified, suggesting fast and remarkable speciation processes. In addition, the genetic, evolutionary, geographic, and phylogeographic evidences reinforced an occurring species complex. Moreover, these evolutionarily significant units (species complex) seem to be inside four natural biogeographic areas. Thus, the genesis and evolution of the Serra do Mar complex might be associated to diversification processes of M. microlepis. Such a consideration suggests that the areas including the upper Iguaçu River and the coastal plains of the states of São Paulo, Paraná, and Santa Catarina require distinct conservation policies involving one of the global biodiversity hotspots, namely, the Brazilian Atlantic Rain Forest.