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Acantholeberis smirnovi Paggi & Herrera-Martinez, 2020 (Cladocera: Acantholeberidae) was recently described from Andean habitats in South America. The presence of a population on the eastern coast of the continent brought the hypothesis of a new Neotropical species different from A. smirnovi. This hypothesis was confirmed from morphological, ecological and biogeographic evidence. Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov. differs from A. smirnovi in the morphology of the head, the valves and the limbs (especially the second and third limbs). Species of Acantholeberis are adapted to live in acid water bodies, with A. accolismaris sp. nov. presenting the same ecological requirements. However, the new species is adapted to live in temporary ponds near the Atlantic Ocean in Brazil in altitudes ranging between 4 and 15 meters above sea level. Considering that Acantholeberidae is an ancient taxon with a pre-Mesozoic origin, geological and environmental changes may have been relevant to speciation and to the observed biogeographic pattern of species of Acantholeberis in Neotropics.

The changes in species composition between habitat patches (beta diversity) are likely related to a number of factors, including environmental heterogeneity, connectivity, disturbance and productivity. Here, we used data from aquatic environments in five Brazilian regions over two years and two seasons (rainy and dry seasons or high and low water level periods in floodplain lakes) in each year to test hypotheses underlying zooplankton beta diversity variation. The regions present different levels of hydrological connectivity, where three regions present lakes that are permanent and connected with the main river, while the water bodies of the other two regions consist of permanent lakes and temporary ponds, with no hydrological connections between them. We tested for relationships between zooplankton beta diversity and environmental heterogeneity, spatial extent, hydrological connectivity, seasonality, disturbance and productivity. Negative relationships were detected between zooplankton beta diversity and both hydrological connectivity and disturbance (periodic dry-outs). Hydrological connectivity is likely to affect beta diversity by facilitating dispersal between habitats. In addition, the harsh environmental filter imposed by disturbance selected for only a small portion of the species from the regional pool that were able to cope with periodic dry-outs (e.g., those with a high production of resting eggs). In summary, this study suggests that faunal exchange and disturbance play important roles in structuring local zooplankton communities.