Genetic polymorphism in prey preference at a small spatial scale:: a case study of soil predatory mites (Hypoaspis aculeifer) and two species of astigmatic mites as prey

Arthropod predators usually feed on a variety of different prey types. At one extreme populations consist of :in ensemble of pure specialists for each prey type and at the other they are composed of generalists that indiscriminately seize any prey encountered. In between these extremes populations may be composed of generalist predators with learned or genetically fixed prey preferences. Here, we report on experimental evidence for genetic variation in prey preference in a local population of the haplo-diploid, soil-inhabiting predatory mite, Hypoaspis aculeifer. A sample of c. 150 predatory mites obtained from c. 0.25 m(2) sandy soil in a lily field (North-Holland), vas collected and their offspring was subjected to selection for prey choice, using two species of astigmatic mites as prey (Rhizoglyphus robini and Tyrophagus putrescentiae, further referred to is prey R and prey T). Individual female predators choosing exclusively prey R or exclusively prey T in three 10-minute dual-choice tests carried out at three-day intervals were set apart and reared (on prey T) as isofemale lines. Four generations of selection yielded three lines showing a high probability of choosing prey R and two lines choosing prey T. Cross-breeding in both directions resulted in hybrid females with intermediate preferences and the choices found in females from F1xParent backcrosses were best explained by assuming monogenic inheritance without dominance. Our selection and cross-breeding experiments demonstrate that polymorphism in prey preference can occur at a very small spatial scale within a local population. We discuss how such variability will alter the dynamics of otherwise monomorphic predator-prey models, and how the simple mode of inheritance of a preference trait can aid the evolution of ecotypes.