Two contrasting views can characterize the attitude of many studies toward reaction norms (RNs). An "optimistic" view attempts to use a linear model to describe RN variation; and a "pessimistic" view emphasizes RNs complexity without using any model to describe them. Here, we have analyzed the shape of 40 RNs of five traits of Drosophila mediopunctata in response to 11 temperatures. Our results, along with several other studies, show that RNs are typically curves best explained by nonlinear models. Estimating the set of 40 RNs on the basis of three rather than 11 temperatures produces a scenario, typical of the pessimistic view, where the linear model is either nonsignificant or a poor explanatory model. Moreover, we show that RN nonlinearity can significantly affect the conclusions of studies using the linear model. We propose a middle ground view on RNs which recognizes their general nonlinearity. Such view could, on the one hand, explain part of the important phenomenon of genotype-environment interaction emphasized by the pessimistic view. Moreover, it may explain features and patterns which are being ignored by the optimistic view. We suggest the parabolic model as first step to reveal patterns which were ignored before, or not fully appreciated. © 2012 The Author(s). Evolution © 2012 The Society for the Study of Evolution.661134043416Andrade, C.A.C., Hatadani, L.M., Klaczko, L.B., Phenotypic plasticity of the aedeagus of Drosophila mediopunctata: effect of the temperature (2005) J. Therm. Biol., 30, pp. 518-523Aubin-Horth, N., Renn, S.C.P., Genomic reaction norms: using integrative biology to understand molecular mechanisms of phenotypic plasticity (2009) Mol. Ecol., 18, pp. 3763-3780Bernardo, U., Pedata, P.A., Viggiani, G., Phenotypic plasticity of pigmentation and morphometric traits in Pnigalio soemius (Hymenoptera: Eulophidae) (2007) Bull. Entomol. Res., 97, pp. 101-109Bitner-Mathé, B.C., Klaczko, L.B., Plasticity of Drosophila melanogaster wing morphology: effects of sex, temperature and density (1999) Genetica, 105, pp. 203-210Byers, D.L., Evolution in heterogeneous environments and the potential of maintenance of genetic variation in traits of adaptive significance (2005) Genetica, 123, pp. 107-124Cabanita, R., Atkinson, D., Seasonal time constraints do not explain exceptions to the temperature size rule in ectotherms (2006) Oikos, 114, pp. 431-440Chevin, L., Lande, R., Mace, G.M., Adaptation, plasticity, and extinction in a changing environment: towards a predictive theory (2010) PLoS Biol., 8, pp. e1000357Coyne, J., Beecham, E., Heritability of two morphological characters within and among natural populations of Drosophila melanogaster (1987) Genetics, 117, pp. 727-737David, J.R., Capy, P., Gauthier, J.P., Abdominal pigmentation and growth temperature in Drosophila melanogaster: similarities and differences in the norms of reaction of successive segments (1990) J. Evol. Biol., 3, pp. 429-445David, J.R., Gibert, P., Gravot, E., Pétavy, G., Morin, J.P., Karan, D., Moreteau, B., Phenotypic plasticity and developmental temperature in Drosophila: analysis and significance of reaction norms of morphometrical traits (1997) J. Therm. Biol., 22, pp. 441-451David, J.R., Gibert, P., Legout, H., Pétavy, G., Capy, P., Moreteau, B., Isofemale lines in Drosophila: an empirical approach to quantitative traits analysis in natural populations (2005) Heredity, 94, pp. 3-12de Jong, G., Quantitative genetics of reaction norms (1990) J. Evol. Biol., 3, pp. 447-468de Jong, G., Evolution of phenotypic plasticity: patterns of plasticity and the emergence of ecotypes (2005) New Phytol., 166, pp. 101-118Delpuech, J.M., Moreteau, B., Chiche, J., Pla, E., Vouidibio, J., David, J.R., Phenotypic plasticity and reaction norms in temperate and tropical populations of Drosophila melanogaster. Ovarian size and developmental temperatures (1995) Evolution, 49, pp. 670-675Elberse, I.A.M., Vanhala, T.K., Turin, J.H.B., Van Damme, J.M.M., Van Tienderen, P.H., Quantitative trait loci affecting growth-related traits in wild barley (Hordeum spontaneum) grown under different levels of nutrient supply (2004) Heredity, 93, pp. 22-33Ellers, J., Driessen, G., Genetic correlation between temperature-induced plasticity of life-history traits in a soil arthropod (2011) Evol. Ecol., 25, pp. 473-484Fogleman, J., A thermal gradient bar for the study of Drosophila (1978) Dros. Inf. Serv., 53, pp. 212-213Fusco, G., Minelli, A., Phenotypic plasticity in development and evolution: facts and concepts (2010) Phil. Trans. R. Soc. B, 365, pp. 547-556Gavrilets, S., Scheiner, S.M., The genetics of phenotypic plasticity. V. Evolution of reaction norm shape (1993) J. Evol. Biol., 6, pp. 31-48Ghalambor, C.K., McKay, J.K., Carroll, S.P., Reznick, D.N., Adaptive versus non-adaptive phenotypic plasticity and the potential for contemporary adaptation in new environments (2007) Funct. Ecol., 21, pp. 394-407Gibert, P., de Jong, G., Temperature dependence of development rate and adult size in Drosophila species: biophysical parameters (2001) J. Evol. Biol., 14, pp. 267-276Gibert, P., Moreteau, B., David, J.R., Scheiner, S.M., Describing the evolution of reaction norm shape: body pigmentation in Drosophila (1998) Evolution, 52, pp. 1501-1506Gibert, P., Capy, P., Imasheva, A., Moreteau, B., Morin, J.P., Petavy, G., David, J.R., Comparative analysis of morphological traits among Drosophila melanogaster and D. simulans: genetic variability, clines and phenotypic plasticity (2004) Genetica, 120, pp. 165-179Gibert, P., Moreteau, B., David, J.R., Phenotypic plasticity of abdomen pigmentation in two geographic populations of Drosophila melanogaster: male-female comparison and sexual dimorphism (2009) Genetica, 135, pp. 403-413Gottlieb, G., Probabilistic epigenesis (2007) Dev. Sci., 10, pp. 1-11Gupta, A.P., Lewontin, R.C., A study of reaction norms in natural populations of Drosophila pseudoobscura (1982) Evolution, 36, pp. 934-948Gutteling, E.W., Riksen, J.A.G., Bakker, J., Kammenga, J.E., Mapping phenotypic plasticity and genotype-environment interactions affecting life-history traits in Caenorhabditis elegans (2007) Heredity, 98, pp. 28-37Hatadani, L.M., Baptista, J.C.R., Souza, W.N., Klaczko, L.B., Colour polymorphism in Drosophila mediopunctata: genetic (chromosomal) analysis and nonrandom association with chromosome inversions (2004) Heredity, 93, pp. 525-534Janion, C., Leinaas, H.P., Terblanche, J.S., Chown, S.L., Trait means and reaction norms: the consequences of climate change/invasion interactions at the organism level (2010) Evol. Ecol., 24, pp. 1365-1380Karan, D., Moreteau, B., David, J.R., Growth temperature and reaction norms of morphometrical traits in a tropical drosophilid: Zaprionus indianus (1999) Heredity, 83, pp. 398-407Karan, D., Morin, J.P., Gibert, P., Moreteau, B., Scheiner, S.M., David, J.R., The genetics of phenotypic plasticity. IX. Genetic architecture, temperature, and sex differences in Drosophila melanogaster (2000) Evolution, 54, pp. 1035-1040Khan, M.A., Bradshaw, A.D., Adaptation to heterogeneous environments. II Phenotypic plasticity in response to spacing in Linum (1976) Aust. J. Agric. Res., 27, pp. 519-531King, E.G., Roff, D.A., Modeling the evolution of phenotypic plasticity in resource allocation in wing-dimorphic insects (2010) Am. Nat., 175, pp. 702-716Kingsolver, J.G., Gomulkiewicz, R., Carter, P.A., Variation, selection and evolution of function-valued traits (2001) Genetica, 112-113, pp. 87-104Kingsolver, J.G., Ragland, G.J., Shlichta, J.G., Quantitative genetics of continuous reaction norms: thermal sensitivity of caterpillar growth rates (2004) Evolution, 58, pp. 1521-1529Krafka, J., The effect of temperature upon facet number in the bar-eyed mutant of Drosophila (1920) J. Gen. Physiol., 2, pp. 409-464Lande, R., Adaptation to an extraordinary environment by evolution of phenotypic plasticity and genetic assimilation (2009) J. Evol. Biol., 22, pp. 1435-1144Levins, R., The strategy of model building in population biology (1966) Am. Sci., 54, pp. 421-431Lewontin, R.C., Annotation: the analysis of variance and the analysis of causes (1974) Am J. Hum. Genet., 26, pp. 400-411Liefting, M., Hoffmann, A.A., Ellers, J., Plasticity versus environmental canalization: population differences in thermal responses along a latitudinal gradient in Drosophila serrata (2009) Evolution, 63, pp. 1954-1963Mal, T.K., Lovett-Doust, J., Phenotypic plasticity in vegetative and reproductive traits in an invasive weed, Lythrum salicaria (Lythraceae), in response to soil moisture (2005) Am. J. Bot., 92, pp. 819-825Moreteau, B., Gibert, P., Delpuech, J.M., Pétavy, G., David, J.R., Phenotypic plasticity of sternopleural bristle number in temperate and tropical populations of Drosophila melanogaster (2003) Genet. Res., 81, pp. 25-32Noach, E.J.K., de Jong, G., Scharloo, W., Phenotypic plasticity of wings in selection lines of Drosophila melanogaster (1997) Heredity, 79, pp. 1-9Nussey, D.H., Wilson, A.J., Brommer, J.E., The evolutionary ecology of individual phenotypic plasticity in wild populations (2007) J. Evol. Biol., 20, pp. 831-844Pérez, A., García, C., Evolutionary responses of Drosophila melanogaster to selection at different larval densities: changes in genetic variation, specialization and phenotypic plasticity (2002) J. Evol. Biol., 15, pp. 524-536Pigliucci, M., Evolution of phenotypic plasticity: where are we going now? (2005) Trends Ecol. Evol., 20, pp. 481-486Reed, T.E., Waples, R.S., Schindler, D.E., Hard, J.J., Kinnison, M.T., Phenotypic plasticity and population viability: the importance of environmental predictability (2010) Proc. R. Soc. B, 277, pp. 3391-3400Rocha, F., Medeiros, H.F., Klaczko, L.B., The reaction norm for abdominal pigmentation and its curve in Drosophila mediopunctata depend on the mean phenotypic value (2009) Evolution, 63, pp. 280-287Scheiner, S.M., Genetics and evolution of phenotypic plasticity (1993) Ann. Rev. Ecol. Syst., 24, pp. 35-68Scheiner, S.M., Lyman, R.F., The genetics of phenotypic plasticity. II. Response to selection (1991) J. Evol. Biol., 4, pp. 23-50Sokal, R.R., Rohlf, F.J., (1995) Biometry: the principles and practice of statistics in biological research, , 3rd ed. W. H. FREEMAN AND CO., New YorkThomas, R.H., Ecology of body size in Drosophila buzzatii: untangling the effects of temperature and nutrition (1993) Ecol. Entomol., 18, pp. 84-90Thomas, R.H., Barker, J.S.E., Quantitative genetic analysis of the body size and shape of Drosophila buzzatii (1993) Theor. Appl. Genet., 85, pp. 598-608Vale, P.F., Stjernman, M., Little, T.J., Temperature-dependent costs of parasitism and maintenance of polymorphism under genotype-by-environment interactions (2008) J. Evol. Biol., 21, pp. 1418-1427Via, S., Adaptive phenotypic plasticity: target or by-product of selection in a variable environment? (1993) Am. Nat., 142, pp. 352-365Via, S., Lande, R., Genotype-environment interaction and the evolution of phenotypic plasticity (1985) Evolution, 39, pp. 505-522Via, S., Gomulkiewicz, R., De Jong, G., Scheiner, S.M., Schlichting, C.D., Van Tienderen, P.H., Adaptive phenotypic plasticity: consensus and controversy (1995) Trends Ecol. Evol., 10, pp. 212-317Weber, S.L., Scheiner, S.M., The genetics of phenotypic plasticity. IV. Chromosomal localization (1992) J. Evol. Biol., 5, pp. 109-120Whitehead, A.N., (1920) The concept of NATURE, , http://www.gutenberg.org/files/18835/18835-h/18835-h.htm, The Tarner Lectures Delivered in Trinity College, November 1919. (1920) The Concept of Nature. Cambridge Univ. Press, Cambridge. Available atWindig, J.J., Genetic correlations and reaction norms in wing pattern of the tropical butterfly Bicyclus anynana (1994) Heredity, 73, pp. 459-470Zar, J.H., (1999) Biostatistical analysis, , Prentice Hall, New JerseyZhang, X., The phenotypic variance within plastic traits under migration-mutation-selection balance (2006) Evolution, 60, pp. 1125-1136