Diapause in the calanoid freshwater copepod Eudiaptomus graciloides

Abstract

The seasonal appearance and the intensity of diapausing-egg production in Eudiaptomus graciloides in five lakes of different size and trophic level were studied. In all lakes, diapausing eggs were produced in autumn. In the large mesotrophic lake Selenter See, the population's shift to the production of diapausing eggs was more complete than in other lakes. We examined day length, temperature and food as proximate factors for the production of diapausing eggs with laboratory experiments. Eudiaptomus graciloides produced diapausing eggs in all treatments, but a significantly higher percentage of diapausing eggs was found under short day conditions except when algal food was abundant and temperature was high. To investigate the adaptive significance of diapause in E. graciloides, we compared the survival of adult and juvenile at different temperatures for E. graciloides with Eudiaptomus gracilis, a sympatric species that does not exhibit diapause. At 8°C, adult E. graciloides survived better than adult E. gracilis and exhibited reduced gut contents and accumulation of storage lipids, traits characteristic, of adult diapause. Eudiaptomus graciloides nauplii did not reach the copepodid stage at 6°C, but E. gracilis nauplii exhibited high mortality and developed very slowly. We hypothesize that adult diapause and production of diapausing eggs facilitate the survival of E. graciloides during cold periods and enhance coexistence with its congener, E. gracilis, in temperate zones.