title: Smells familiar: group-joining decisions of predatory mites are mediated by olfactory cues of social familiarity.
abstract: Group-living animals frequently have to trade off the costs and benefits of leaving an established group and joining another group. Owing to their high fitness relevance, group-joining decisions are commonly nonrandom and may be based on traits of both individual members and the group such as life stage, body size, social status and group density or size, respectively. Many group-living animals are able to recognize and to associate preferentially with familiar individuals, i.e. those encountered before. Hence, after dispersing from established groups, animals commonly have to decide whether to join a new familiar or unfamiliar group. Using binary choice situations we assessed the effects of social familiarity on group-joining behaviour of the plant-inhabiting predatory mitePhytoseiulus persimilis. Group living inP. persimilisis brought about by the patchy distribution of its spider mite prey and mutual conspecific attraction. In the first experiment, gravid predator females given a choice between spider mite patches occupied by unfamiliar and familiar groups of females strongly preferred to join familiar groups and to deposit their eggs in these patches. Preference for socially familiar groups was robust across biases of spider mite prey densities between choice options. The second experiment revealed that the predatory mite females can smell social familiarity from a distance. Females subjected to odour choice situations in artificial cages were more strongly attracted to the odour of familiar than unfamiliar groups. We argue thatP. persimilisfemales preferentially join socially familiar groups because a familiar social environment relaxes competition and optimizes foraging and reproduction.
authors.affiliation: Group of Arthropod Ecology and Behavior, Division of Plant Protection, Department of Crop Sciences, University of Natural Resources and Life Sciences, Vienna, Austria.
authors.forename: Muluken G
authors.initials: MG
authors.lastname: Muleta
authors.forename: Peter
authors.initials: P
authors.lastname: Schausberger
keywords: Phytoseiulus persimilis; familiarity; group living; joining behaviour; olfactory cue; predatory mite; preference; prey density
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