Effects of temperature on reproductive output, egg provisioning, juvenile hormone and vitellogenin titres in the butterfly Bicyclus anynana Thorin L. Geister a, *, Matthias W. Lorenz a , Martina Meyering-Vos a , Klaus. H. Hoffmann a , Klaus Fischer a,b a Department of Animal Ecology I, University of Bayreuth, P.O. Box 101 251, D-95440 Bayreuth, Germany b Zoological Institute & Museum, University of Greifswald, D-17489 Greifswald, Germany 1. Introduction Environmental effects on the expression of the phenotype, called phenotypic plasticity, are widespread in nature (Endler, 1986; Ghalambor et al., 2007; Miner et al., 2005; Nussey et al., 2007; Pigliucci, 2005). Such plastic changes to the phenotype may either comprise merely biochemical or physiological interactions of the organism with its environment, or may be adaptations to spatially heterogeneous or temporarily varying environments (Bradshaw, 1965; Levins, 1963). Consequently, much effort has been devoted to distinguishing between both scenarios over recent decades (e.g. Blanckenhorn, 2000; Fischer et al., 2003a; Gotthard and Nylin, 1995; Pigliucci, 2005). Comparably less effort, in contrast, has been dedicated to disentangling the mechanistic basis of phenotypic plasticity (Brakefield et al., 1998; Hodin and Riddiford, 2000; Zera, 2003). Understanding the regulation of plasticity poses an exciting challenge, though, as environmental effects need to trigger different developmental pathways present within the same genotype (Flatt et al., 2005; Nijhout, 1999; Pigliucci, 2005; Sinervo and Svensson, 1998; Zera, 2007). In insects, juvenile hormones (JHs) and 20-OH ecdysone are important regulators of key aspects of their life histories, and are therefore good candidates for the regulation of phenotypic plasticity (Ga ¨ de et al., 1997; Nijhout, 1994). Indeed, traits known to be under hormonal control include metamorphosis, behaviour, caste determination, reproduction and polymorphisms (e.g. de Wilde and Beetsma, 1982; Dingle and Winchell, 1997; Emlen and Nijhout, 1999; Ga ¨de et al., 1997; Gilbert et al., 2000; Hoffmann, 1995; Nijhout, 1994). Hormones therefore provide a mechanistic link between environments, genes and trait expression (Finch and Rose, 1995; Flatt et al., 2005; Sinervo and Svensson, 1998). In the tropical butterfly Bicyclus anynana, for instance, seasonal wing polyphenism is under hormonal control, being induced during pupal development (Koch et al., 1996; Zijlstra et al., 2004). The same species shows pronounced temperature-mediated plasticity in egg size, producing larger eggs at lower temperatures and vice versa (Fischer et al., 2003a,b,c), which is a common feature in ectothermic animals (Atkinson, 1994; Blanckenhorn, 2000; Ernsting and Isaaks, 2000; Yampolski and Scheiner, 1996). Several lines of evidence indicate that in B. anynana this plastic response comprises an adaptation to the alternate wet-dry Journal of Insect Physiology 54 (2008) 1253–1260 ARTICLE INFO Article history: Received 9 April 2008 Received in revised form 2 June 2008 Accepted 4 June 2008 Keywords: Phenotypic plasticity Egg composition Egg size Hormonal control Fecundity Insect Reproductive investment ABSTRACT Environmentally induced phenotypic plasticity is common in nature. Hormones, affecting multiple traits and signaling to a variety of distant target tissues, provide a mechanistic link between environments, genes and trait expression, and may therefore well be involved in the regulation phenotypic plasticity. Here, we investigate whether in the tropical butterfly Bicyclus anynana temperature-mediated plasticity in egg size and number, with fewer but larger eggs produced at lower temperatures and vice versa, is under control of juvenile hormone, and whether different temperatures cause differences in egg composition. Female B. anynana butterflies showed the expected response to temperature, however, we found no evidence for an involvement of juvenile hormone. Neither haemolymph JH II and JH III titres nor vitellogenin levels differed across temperatures. The smaller eggs produced at the higher temperature contained relatively higher amounts of water, free carbohydrates and proteins, but relatively lower amounts of lipids. While these smaller eggs had a lower absolute energy content, total reproductive investment was higher at the higher temperature (due to a higher fecundity). Overall, our study indicates that temperature-mediated plasticity in reproduction in B. anynana is mechanistically related to a biophysical model, with oocyte production (differentiation) and oocyte growth (vitellogenesis) having differential temperature sensitivities. ß 2008 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +49 921 553079; fax: +49 921 552784. E-mail address: thorin.geister@uni-bayreuth.de (T.L. Geister). Contents lists available at ScienceDirect Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys 0022-1910/$ – see front matter ß 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2008.06.002