First record of planktonic crustaceans in Sardinian reservoirs

Sardinian man-made lakes are reservoirs of species richness, hosting zooplankton taxa from the Mediterranean region and North Africa. To provide a first record of the taxa composition and diversity of zooplankton communities, we sampled 15 reservoirs during 2008-2009, from the north of the island to the south, representative of a range of size, depth, renewal time, and trophy. The survey was complemented by seasonal sampling in one of the largest lakes studied. Water samples collected from surface to bottom provided data on hydrochemistry and trophy. Crustacean dormant stages were inspected from sediments of the richest, and most diverse, Lake Sos Canales. RDA suggested that productivity, water depth, renewal time and altitude were the main variables related to taxa composition. The ubiquitous Copidodiaptomus numidicus, and its persistence in the water column, resulted from the production of subitaneous eggs throughout the year, an adaptive strategy in perennial water bodies. Genetic analyses of DNA sequences of the diagnostic gene ND5 placed the Sardinian Daphnia pulex in the North American group. Moreover, the ND5 sequence found in Sardinia was identical with that of an asexual hybrid clone between the American D. pulex and American D. pulicaria that replaced native D. pulex throughout Africa. The presence of this ND5 haplotype in Sardinia shows that this invasive clone also poses an invasive threat to native populations in Europe.