Phenology of Daphnia in a Northern Italy pond during the weather anomalous 2014

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Abstract
This note reports a comparison between Daphnia phenology in the weather anomalous 2014 and a previous three years period (2011-2013), in a shallow water body of Northern Italy (Bodrio del pastore III) where we recorded D. pulex. In 2011-2013, Daphnia population showed 1-2 density peaks from mid spring to early summer, it declined in July-August and did not recover, from ephippia, until the following spring. The seasonal dynamics was probably related to the species thermal tolerance. Males and ephippial females appeared at the beginning of growth season according to a typical feature of Daphnia populations from temporary habitats. The presence of the Chaoborus larvae resulted in juvenile adaptive predator-avoidance cyclomorphosis. In 2014, in the study area, mean winter air temperature was much warmer than average recorded during the past three years while it was much colder than average in July and August. This reflected the relatively rainy and cloudy summer months: the winter and summer precipitations total was above the previous three years average. In 2014, Daphnia was found all over the year and showed a maximum peak of density in November. The general increase of Daphnia was related to a shift in D. pulex population phenology, seasonal growth started earlier and lasted longer, and to the occurrence of D. longispina. Both species were identified by genetic markers and phylogenetic analyses of ND5 sequences placed isolates from the Bodrio del pastore III into the European D. pulex group. Both populations reproduced by cyclical parthenogenesis and showed cyclomorphosis. However, D. pulex produced more males and ephippial females than D. longispina. Their seasonal dynamics were quite different: D. longispina dominated in late summer while D. pulex showed the highest density in November. The presence of D. pulex in the Bodrio is important in the framework of conservation ecology especially because we have showed that it is native European strain instead of the invasive North American clone that replaced native D. pulex throughout Africa and was already recorded in Italy. We provide some indications and discuss how Daphnia phenology of shallow lakes of temperate areas may be susceptible to inter-annual variability in weather conditions.

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