Heterocypris (Crustacea: Ostracoda) from the Isole Pelagie (Sicily, Italy):: hatching phenology of resting eggs

The hatching phenology of Heterocypris resting eggs was investigated in laboratory controlled conditions. Microcosms were set up using dry sediments from three freshwater temporary ponds (Cavallo Bianco, Aria Rossa and Vallone della Forbice) of the island of Lampedusa (Sicily) and kept at different temperatures and photoperiods. Hatching time was modulated by different environmental factors. initial anoxia, induced by the decomposition of the sediment's organic matter, delayed hatching in the microcosm set up with sediments from Vallone della Forbice which has a high organic matter content. Temperature and photoperiod in isolation did not seem to affect hatching significantly, while their interaction did. The coexistence of two female morphotypes with different reproductive modes could not be explained by a differential response to temperature and photoperiod. Coexistence was probably due to disturbance events, such as drying up of ephemeral pools. Some resting eggs (in different percentages in different microcosms) hatched only after a second hydration (after microcosms dried up). Hatching phenology is discussed in relation to genetic differences in egg responsiveness to hatching stimuli and to a bet-hedging strategy in a year-to-year highly variable environment such as the ephemeral ponds of Lampedusa.