Original paper

To rest in hydration: hatching phenology of resting eggs of Heterocypris incongruens (Crustacea: Ostracoda)

Rossi, Valeria; Albini, Dania; Benassi, Giorgio; Menozzi, Paolo

Abstract

The ability of resting eggs to survive periods of drying, and hydroperiods that are too short to allow reproduction, affects the ability of a species to colonise and persist in temporary waters. We previously described the formation of an egg bank of Heterocypris incongruens, a widespread and common freshwater ostracod. The egg bank was made up of genetically homogeneous resting eggs produced by a laboratory clonal lineage that we used to colonise a pond with an unpredictable hydroperiod. Here we report on laboratory experiments on the study of hatching phenology of resting eggs from the newly established egg bank. We measured the hatching percentage and egg bank depletion during four successive inundations (followed by dry periods) without reproduction. In a first factorial experiment, egg hatching was assessed under the following set of conditions: egg age (3 or 15 months), inundation photoperiod (12:12 L:D or 16:8 L:D), water quality (mineral water or adult-conditioned water). In a second experiment egg hatching in four successive inundations was assessed varying the duration of the first inundation (6 or 30 days). Our estimation of resting egg density in the pond was 65×104 eggs m−2. A total of 7133 hatchings were recorded, about 80% were observed in the first inundation while the rest occurred in three subsequent inundations. Egg age and photoperiod had no effect on hatching percentage while metabolites produced by adult females in conditioned water had a negative effect. Short inundation did not affect hatching percentages or resting egg survivorship. Hatching in successive inundations did not depend on genetic differences among eggs and the process may be considered a stochastic switching of a single genotype among different phenotypes. Such a hatching phenology ensures a risk spreading response that is advantageous in highly stochastic environments. It prevents population extinction following very short hydroperiods and for at least four subsequent generations of failed reproduction.

Keywords

freshwater temporary pondegg bank depletionrisk-spreading