SHADE AND HERBIVORY INDUCE FLUCTUATING ASYMMETRY IN A MEDITERRANEAN OAK Carolina Puerta-Pin ˜ ero, 1 Jose ´ Marı ´a Go ´mez, and Jose ´ A. Ho ´dar Departamento de Ecologı ´a, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain Fluctuating asymmetry (FA), random nondirectional deviations from perfect symmetry, has been proposed as a useful indicator of environmental stress. Nevertheless, FA acts as a nonspecific indicator of stress; thus, factorial designs are needed to disentangle which of the factors may induce FA. We used an experimental approach in which seedlings of Quercus pyrenaica were exposed to two levels of light, water, and simulated herbivory. To determine whether FA may operate as a stress indicator, leaf width and number of lobes were measured. Our predictions were (1) different levels of light, water, and herbivory can bring different levels of FA and (2) fluctuating asym- metry can act as an early stress indicator. As predicted, FAwas higher in shade than in sun, both for leaf width and number of leaf lobes. By contrast, pruning affected FA only for number of lobes. FAwas higher in pruned seedlings in the sun but lower in pruned seedlings in the shade. The two FA indices used (jL  Rj and Var L  R ð Þ, where L and R represent the left and right leaf sides) gave similar results. Because leaf FA in Q. pyrenaica increased with low light radiation and simulated herbivory and both are important in the dynamics of Mediterranean communities, FA appears to be a possible tool as an indicator of environmental stress. Keywords: environmental stress, fluctuating asymmetry, light, Quercus pyrenaica, simulated herbivory. Online enhancements: appendix tables. Introduction Fluctuating asymmetry (FA), small nondirectional deviations from bilateral symmetry, is thought to represent a direct mea- sure of the ability of individuals to control their development (Van Valen 1962; Polak 2003). Many studies have associated FA measurements with individual fitness components (Møller 1997; Polak 2003) and environmental stresses (Parsons 1990; Tracy et al. 2003). At the moment, one of the main hypotheses within FA-stress studies is that stress contributes to flawed de- velopment of individuals—i.e., stress can generate FA—and thus FA can be an indicator of developmental instability (Møller 1995; Zvereva et al. 1997; Hagen et al. 2003). However, FA acts as a nonspecific indicator of stress, and only some prior studies have reproduced natural conditions (Møller 1995; Rettig et al. 1997). Additionally, most consider only a single stress factor at a time (Møller 1995, 1998; Kozlov et al. 1996; Zvereva et al. 1997; Eeva et al. 2000; Zvereva and Kozlov 2001; Cornelissen et al. 2003; Hagen et al. 2003; Kristensen et al. 2003; Sinclair and Hoffmann 2003; Cornelissen and Stiling 2005), while much less attention has been paid to the interaction between simultaneous stresses (Leung et al. 2000; but see Hochwender and Fritz 1999; Roy and Stanton 1999). In our opinion, this implies that potential studies should con- sider natural conditions, in addition to factorial designs, which are crucial to disentangling which factors induce FA and thus enhance the relevance of the use of FA as a stress indicator. In the Mediterranean region, herbivory, drought, and light (as shading or photoinhibition) emerge as the most common stresses affecting plant performance (Valladares 2004). Previ- ous studies have demonstrated that light, water, and herbivory, which affect morphological and chemical plant traits, can act as stressful factors in Quercus pyrenaica both in the field (Go ´ mez et al. 2003) and in experimental studies (Baraza et al. 2004). In fact, Baraza et al. (2004) used the same seedlings as those used for this study. For this study, we define stress as any envi- ronmental factor causing a change in a biological system that is potentially harmful (Hoffmann and Parsons 1994). Thus, seed- lings with lower growth and less chemical defenses in Baraza et al.’s (2004) study were considered to be under stress. Within this scenario, it is possible for FA be used to obtain an objective index that assesses the effect of stress on plants (Bultman and Faeth 1987; Møller 1995). Our focal hypothesis was that natu- ral populations suffering from stress should display FA. Quer- cus pyrenaica seedlings were exposed to different levels of light, water, and simulated herbivory, mimicking natural conditions (Go ´mez et al. 2003; C. Puerta-Pin ˜ero, J. M. Go ´mez, and J. A. Ho ´ dar, personal observations). Our major predictions were (1) simulated herbivory and low light intensity (factors that neg- atively affected seedling performance in Baraza et al. 2004) result in FA, and thus, (2) FA can be used as an early stress indi- cator of these types of stress for this species. Material and Methods Seeds and Seedlings In autumn 1997, several thousand ripe Quercus pyrenaica acorns were collected from at least 20 trees (37°059N, 3°269W, 1 Author for correspondence; e-mail: carol@ugr.es. Manuscript received October 2007; revised manuscript received October 2007. 631 Int. J. Plant Sci. 169(5):631–635. 2008. Ó 2008 by The University of Chicago. All rights reserved. 1058-5893/2008/16905-0005$15.00 DOI: 10.1086/533601