‘‘Personality’’ Variation in a Clonal Insect: The Pea Aphid, Acyrthosiphon pisum ABSTRACT: Individuals are often consistent in their behavior but vary from each other in the level of behavior shown. Despite burgeoning interest in such animal personality variation, studies on invertebrates are scarce, and studies on clonal invertebrates nonexistent. This is surprising given the obvious advantages of using invertebrates/clones to tackle the crucial question why such consistent behavioral differences exist. Here we show that individuals of clonal pea aphids exhibit consistent behavioral differences in their escape responses to a predator attack (dropping vs. nondropping off a plant). However, behavior was not repeat- able at the clonal level. Genetically identical clones expressed various pheno- types but different clones produced different proportions of each phenotype (dropper, nondropper, and inconsistent). Manipulations of early environmental conditions had little qualitative impact on such patterns. We discuss the import- ance of our findings for future studies of the evolutionary and ecological consequences of personality variation. ß 2011 Wiley Periodicals, Inc. Dev Psychobiol 53: 631–640, 2011. Keywords: personality; risk-taking; predation; temperament; behavioral variation; behavioral consistency; environment; Acyrthosiphon pisum; pea aphid; Coccinella septempunctata; clone INTRODUCTION There is a growing body of evidence for the existence of personality variation in animals (e.g., Gosling, 2001; Sih, Bell, Johnson, & Ziemba, 2004). Such personality variation has two features: (i) individuals are consistent in their behavior over time and/or contexts and (ii) they differ from each other in the level of behavior they express (e.g., Dall, Houston, & McNamara, 2004). The cooccurrence of these two features is evolutionary intri- guing since individuals are often presumed to be plastic in their behavior, so that they can adapt to current environmental conditions (e.g., Dall et al., 2004; Sih et al., 2004). Despite burgeoning interest in the exist- ence of personality variation our understanding about its function is still unclear. Yet, evolutionary and eco- logical consequences of personality are expected to be vast, with influences on for instance population ecology/dynamics (Sih et al., 2004) and the evolution of cooperation (Dall et al., 2004). Therefore a detailed understanding of personality variation is crucial for behavioral ecology. Recently, a number of theoretical considerations and frameworks have been put forward to explain the function of personality variation (reviewed in Sih & Bell, 2008; Schuett, Tregenza, & Dall, 2010) but empirical tests of such hypotheses are still widely lacking. This might be for a number of reasons. Most of the postulated hypotheses are based on various types of selection, such as fluctuating selec- tion (Mangel, 1991), negative frequency-dependent selection (Wilson, Clark, Coleman, & Dearstyne, 1994; Developmental Psychobiology Wiebke Schuett 1 Sasha R.X. Dall 2 Jana Baeumer 1 Michaela H. Kloesener 1 Shinichi Nakagawa 3 Felix Beinlich 1 Till Eggers 1,4 1 Experimental Ecology Group Department for Biology and Chemistry University of Osnabrueck Barbarastrasse 11, 49069 Osnabrueck Germany E-mail: wiebkesch@googlemail.com 2 Centre for Ecology and Conservation School of Biosciences University of Exeter, Cornwall Campus Penryn, Cornwall TR10 9EZ, UK 3 Department of Zoology University of Otago 340 Great King Street Dunedin, New Zealand 4 Agricultural Products Global Research Data Management and Biometrics BASF The Chemical Company Carl Bosch Str., 67117 Limburgerhof Germany Received 21 September 2010; Accepted 28 January 2011 Wiebke Schuett present address is Finnish Museum of Natural History, FI-00014 University of Helsinki, P.O. Box 17, Helsinki, Finland. Correspondence to: W. Schuett Published online 1 March 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/dev.20538 ß 2011 Wiley Periodicals, Inc.