Does artificial selection for fixed prey preference affect learning in a predatory mite? Experiments to unravel mechanisms underlying polyphagy in Hypoaspis aculeifer

Abstract

Individual reproductive success in polyphagous arthropod predators critically depends on the prey species included in their diet. Hence, selection will act on traits that enable the predator to tune its preference to the best prey available. Such traits may be either rigid or flexible and are manifested as genetically fixed or learned preferences. Whether these two types of behaviour are mutually exclusive or manifest themselves in condition-dependent ways, is still an open question. We sought possible answers by studying a soil-dwelling predatory mite (Hypoaspis (Gaeolaelaps) aculeifer Canestrini), known to exhibit a genetic polymorphism in prey preferences within local populations. We had previously shown that 4 generations of artificial selection on the choice for either of two astigmatic mites (Rhizoglyphus robini and Tyrophagus putrescentiae) resulted in isofemale lines with contrasting prey preferences (<I>R</I>-line and <I>T</I>-line) and that the preference traits are inherited as though they are monogenic without dominance. In this article, we ask whether artificial selection has influenced the ability to switch preferences in a condition-dependent way. First, we conditioned the female predators of both isofemale lines by starving them in the presence of odour from each of the two prey species separately or in the absence of any prey odour. Then, at least half an hour later, we assessed their prey preference in two-choice tests. When starved in presence of odour from non-preferred prey, both lines show a slight but non-significant increase in preference for their preferred prey. However, when starved in presence of odour from the preferred prey, predators of both lines showed a clear and significant switch toward the alternative prey. This shows the ability of predatory mites to memorize the odour experienced during starvation, and to change their prey preference. It also shows that - despite four generations of artificial selection for a fixed prey preference - they retain the ability to exhibit a form of learning and to switch preferences. This result sheds new light on the impact of selection on fixed and flexible prey preferences in polyphagous arthropod predators that experience different dominant prey species in space and time.