Effects of chronic exposure to a toxic prey in a generalist predator

Abstract.  Generalist predators experience large differences in prey quality, and eating toxic prey may affect their fitness even if the toxic prey constitutes only a small fraction of a mixed diet. Feeding and life history parameters were examined in the wolf spider Pardosa prativaga during continuous exposure to the toxic collembolan Folsomia candida . Spiderlings were divided into a control group fed adult Drosophila melanogaster , a group fed only F. candida , and a mixed diet group fed both types of prey. Folsomia candida reduced survival, developmental stage attained and growth rate of all exposed spiders. Spiders chronically exposed to F . candida increased their consumption of D. melanogaster compared to control spiders. Folsomia candida thus inhibited the utilization of the high-quality food and/or increased the respiration rate. The intake of F . candida remained at a constant low level throughout the experiment, indicating that P. prativaga was unable to develop an absolute aversion against this prey. Half of the control group was also given the mixed diet after a large juvenile instar was attained. These spiders were not affected to the same extent as the newly hatched spiderlings, indicating an ontogenetically increased tolerance. Comparison of laboratory-raised and field-caught spiders confirmed that tolerance to F. candida was size-dependent and thus not an induced response. A differential survival in the mixed diet group, based partly on maternal effects, indicated possible genetic variability in the physiological tolerance to F. candida .