Hatching rate and diapause duration in eggs of Paracartia latisetosa (Copepoda: Calanoida)

Abstract

Paracartia latisetosa is a seasonally dominant copepod species in Mediterranean coastal waters. This species is well known for the production of diapause eggs which allow it to over-winter. Diapause eggs are morphologically distinguishable (they have long spines on the chorion) from subitaneous eggs (which are smooth or only have short spines). From September 2003 to December 2004, eggs produced by 329 adult females (collected biweekly and incubated for 24 h) were maintained under constant conditions until hatching. Subitaneous eggs were produced on all sampling dates and hatched during the first week after laying. Diapause eggs were produced from September to December and they hatched after a period of obligatory rest (from 54 to 202 days). Variability of life history traits (egg production, hatching rate, diapause duration) have been interpreted as an adaptation of the species to high environment variability. Regression analysis showed that the diapause duration was positively correlated with photoperiod length at the time of collection of the adults. As a result of this range in resting time, the majority of diapausing eggs hatched in February–March. This fact, as they are not influenced by external stimuli, suggests that the timer of diapause duration of the eggs is under parental control.