Contrasting life history responses to fish released infochemicals of two co-occurring Daphnia species that show different migration behaviour

In a previous field study (Flik & Vijverberg 2003) we showed that in an oligotrophic-mesotrophic lake in the Netherlands (L. Maarsseveen) two co-occurring Daphnia species, Daphnia pulicaria and Daphnia galeata x hyalina performed distinct vertical migration behaviour during summer which is induced by a high fish biomass of young perch. During late spring and summer, D. galeata × hyalina exhibits diel vertical migration, whereas D. pulicaria is staying down day and night in the hypolim- nion. This difference in migration behaviour results in contrasting predation mortalities caused by fish, low for D. pulicaria and relatively high for D. galeata × hyalina. In the present study, we measured in the laboratory the effects of fish released infochemicals on five life history traits in four genetically distinct D. galeata × hyalina and three ge- netically distinct D. pulicaria clones collected during summer at day-time from the hypolimnion. We tested the hypothesis that the species which behaviour is providing the best protection against fish predation (i. e. D. pulicaria) is less protected by life his- tory traits induced by fish released infochemicals than the species which by its behav- iour is less well protected against fish predation (i. e. D. galeata × hyalina). Our results show that D. galeata × hyalina responded in three out of five traits differently to fish infochemicals than D. pulicaria. In all these three traits D. galeata × hyalina re- sponded significantly to fish-released infochemicals, whereas D. pulicaria did not show any significant response at all. We conclude that in D. pulicaria behavioural de- fences trade-off against life history defences.