Differential responses of zooplankton assemblages to environmental variation in temporary and permanent ponds

Permanent and temporary wetlands in Mediterranean shrublands represent unique repositories of biodiversity, which are increasingly threatened by human-induced habitat loss. The zooplankton of a permanent (P1) and a temporary pond (T35) in the Natural Reserve of Castelporziano, a rare residual stretch of such a shrubland in Central Italy (Latium), was investigated to: (1) expand and deepen knowledge of these endangered freshwater habitats, which represent a crucial component of Mediterranean biodiversity; (2) identify environmental controls regulating the development of zooplankton communities of each environment; and (3) highlight differences in the adaptive responses of the zooplankton community in relation to the different ecological conditions experienced by permanent and temporary habitats. Despite summer desiccation in T35, the two ponds exhibited a relative homogeneity in hydrological and physico-chemical dynamics. Zooplankton assemblages contained 41 total taxa, of which 32 were found in P1 and 28 in T35. Out of the 41 taxa identified, 22 (> 50%) were exclusively present in one of the two ponds. On a yearly basis, the community dynamics of P1 seemed to be conditioned by physical and chemical factors and by hydrological cycle characteristics, while the community of T35 responded to algal blooms, food competition and predator/prey equilibria rather than correlating to abiotic factors. The main differences amongst zooplankton assemblages were observed over short time scales and occurred both within and between seasons, highlighting the role of some structural taxa that dominated the average composition of the community throughout the year, and the importance of "quick-response" taxa in determining the short-term composition and structure variation of pond zooplankton. A year-round cyclic community succession peculiar to each pond is described

Polymorphisms in predator induced defences of coexisting Daphnia pulex and D. longispina

A comparison of juvenile predator-avoidance polymorphisms of Daphnia pulex and D. longispina in a shallow water body of Northern Italy is reported. The presence of the Chaoborus larvae resulted in juvenile adaptive predator-avoidance cyclomorphosis in both species. The frequency of induced morphotypes was higher in the small-sized D. longispina than in the large-sized D. pulex. Relative tail-spine size was higher in D. longispina than in D. pulex. D. longispina displayed much more responsiveness to Chaoborus than D. pulex. Both species showed at least 6 different defensive morphotypes that were classified according to the neckteeth number, the neckteeth position and the thickness of occipital epithelia under neckteeth. The frequencies of different morphotypes varied significantly between species. The developmental responses of Daphnia to the presence of predators are regulated at various levels, according to specific timelines of kairomone sensitive phases and developmental frame of defense trait formation. Variation of a specific timeline might be linked to flexibility in developmental responses of Daphnia to Chaoborus and seasonal variation in the frequencies of various morphotypes. Cyclomorphosis should not only be due to changes in environmental factors that directly affects risk, but also to ones that act as proxy signaling changes in predation risk