There are only a few studies about the ostracod faunal assemblages and their environmental requirements from Patagonia (e.g. CUSMINSKY et al., 2011; RAMÓN MERCAU et al., 2012). Here we present the results of a survey of thirteen water bodies (streams, springs, temporary habitats) in Northern Patagonia (39° 52’ – 41°50’ S; 70°36’ – 71°27’ W) and their comparison with those of previous studies in the earstern Patagonia. The goal of this research is to enhance our understanding of the regional Patagonian ostracoda fauna and evaluate the relationship between ostracod species and physical and chemical (depth, temperature, pH, conductivity, dissolved oxygen concentration, seston and main ions) parameters of host waters along a W-E precipitation gradient (ranging from 1200 to 160mm/annually). To date, seven species were identified: Amphicypris nobilis Sars 1901, Bradleystrandesia fuscata (Jurine, 1820), Cypridopsis vidua (O. F. Müller, 1776), Cypris pubera O. F. Müller 1776, Eucypris virens (Jurine, 1820), Heterocypris incongruens (Ramdohr, 1808) and Tonnacypris lutaria (Koch, 1838). The more frequent species were T. lutaria and E. virens, while A. nobilis and C. vidua were only found in one site. Males of A. nobilis were found while the other species were represented only by females. The environment of this fauna is related to low conductivity and salinity in the water. Conversely, previous studies in the easternmost area of Patagonia have shown different fauna such us Penthesinelula incae (Delachaux, 1928), Potamocypris smaradigma (Vávra, 1891), Ilyocypris ramirezi Cusminsky and Whatley, 1996, Limnocythere patagonica Cusminsky and Whatley, 1996, Eucypris fontana (Graf, 1931), Kapcypridopsis megapodus Cusminsky et al. 2005 and Limnocythere rionegroensis, Cusminsky and Whatley, 1996 living in comparatively higher conductivity (CUSMINSKY et al., 2011). The latter suggest that the decreasing precipitation trend towards eastern Patagonia is reflected in the distribution of different ostracod fauna association. On the other hand, new distributions of cosmopolitan species are present, spreading out their geographical distribution to the Neotropical region (MARTENS et al., 2008). Some of the species such us C. pubera, E. virens and B. fuscata have been also described in the Neartic region, suggesting that birds could be responsible to their dispersion. However, the mode of dispersion of T. lutaria in this region is still an open question.Fil: Coviaga, Corina Anabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Cusminsky, Gabriela Catalina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Perez, Alejandra Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Diaz, Analia Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Schwalb, Antje. Technische Universitat Carolo Wilhelmina Zu Braunschweig. Iinstitut fur Geosysteme und Bioindikation.; AlemaniaFil: Alperin, Marta Ines. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Cátedra de Estadística; ArgentinaFil: Viehberg, Finn. University of Cologne.Institute of Geology and Mineralogy; AlemaniaFil: Whatley, Robin. University Aberystwyth.Institute of Earth Studies.Department of Geology; Reino UnidoFil: Ariztegui, Daniel. University of Geneva.Department of Earth Sciences; SuizaFil: Markgraf, Vera. University of Colorado; Estados Unidos. Northern Arizona University.; Estados Unido
