Exposure to fish kairomones and defended morph prey affects chaoborus life history strategy and morphology

Larvae of the Phantom midge Chaoborus are involved in an intraguild food web with Daphnia pulex as the basal resource and plantivorous fish as the intraguild predator. Chaoborus prey on D. pulex and are themselves prey for fish that also consume D. pulex. In this study an experiment was carried out to assess the impact on Chaoborus of poorer quality (defended morph) prey and exposure to predator kairomones. A great deal of research has been conducted detailing the morphological, behavioural and life history responses of Daphnia pulex in response to the presence of predatory Chaoborus larvae although far less attention has been paid to the effects these D. pulex defences have on Chaoborus. Chemical cues have also been seen to induce diel vertical migration in Chaoborus larvae. Data presented here show the presence of fish chemical cues cause Chaoborus to pupate sooner but with reduced reproductive investment. Fish chemicals also had an effect on gut morphology as individuals raised in water containing fish had smaller, lighter toned guts. Smaller diameter guts may be less efficient, leading to reduced energy intake rates and may be the cause of the reductions in reproductive effort. As fish are visual hunters it is thought increased transparency offers a benefit in terms of reduced predation but incurs a cost in terms of reduced efficiency. Feeding on defended morph prey also caused Chaoborus to pupate later, suggesting Chaoborus larvae foraging on defended morph individuals pay a cost in terms of reduced population growth rate.