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Miller, S. E., Novotny, V. & Basset, Y. in Foundations of Tropical Biology: Key Papers and Commentaries(eds Chazdon, R. L. & Whitmore, T. C.) (Univ. Chicago Press, Chicago, in the press).22. Leps, J., Novotny, V. & Basset, Y. Habitat and successional optimum of plants and the composition oftheir leaf-chewing herbivores in Papua New Guinea. J. Ecol. 89, 186–199 (2001).23. Basset, Y., Novotny, V., Miller, S. E. & Pyle, R. Quantifying biodiversity: experience withparataxonomists and digital photography in Papua New Guinea and Guyana. BioScience 50, 899–908(2000).24. Angiosperm Phylogeny Group An ordinal classification for the families of flowering plants. Ann.Missouri Bot. Gard. 85, 531–553 (1998).25. Weiblen, G. D. Phylogenetic relationships of functionally dioecious Ficus (Moraceae) based onribosomal DNA sequences and morphology. Am. J. Bot. 87, 1342–1357 (2000).26. Backlund, M., Oxelman, B. & Bremer, B. Phylogenetic relationships within the Gentianales based onndhF and rbcL sequences, with particular reference to the Loganiaceae. Am. J. Bot. 87, 1029–1043(2000).27. Soltis, D. E. et al. Angiosperm phylogeny inferred from 18S rDNA, rbcL, and atpB sequences. Bot.J. Linn. Soc. 133, 381–461 (2000).28. Qiu, Y.-L. et al. The earliest angiosperms. Evidence from mitochondrial, plastid and nuclear genomes.Nature 402, 404–407 (1999).29. Bremer, B. et al. More characters or more taxa for a robust phylogeny—case study from the coffeefamily (Rubiaceae). Syst. Biol. 48, 413–435 (1999).30. Powell, J. A., Mitter, C. & Farrell, B. in Lepidoptera, Moths and Butterflies Vol. 1: Evolution, Systematics,and Biogeography (ed. Kristensen, N. P.) 403–422 (Walter de Gruyter, Berlin, 1998).AcknowledgementsWe thank parataxonomists J. Auga, W. Boen, C. Dal, S. Hiuk, B. Isua, M. Kasbal, R. Kutil,M. Manumbor and K. Molem and also K. Darrow and N. Heidari for assistance; manyinsect collectors and taxonomists are acknowledged elsewhere. N. Stork, T. Lewinsohn,J. Zrzavy, J. Leps and A. Stewart commented on the manuscript. This work was supportedby the National Science Foundation (USA), Christensen Fund (USA), Grant Agency of theCzech Republic, Czech Academy of Sciences, the Swedish Natural Science ResearchCouncil, Czech Ministry of Education, Otto Kinne Foundation, Darwin Initiative (UK),International Centre of Insect Physiology and Ecology (ICIPE) and Bishop Museum.Competing interests statementThe authors declare that they have no competing financial interests.Correspondence and requests for materials should be addressed to V.N.(e-mail: [email protected])...............................................................Developmental constraints versusflexibility in morphological evolutionPatrı´cia Beldade, Kees Koops & Paul M. BrakefieldInstitute of Evolutionary and Ecological Sciences, Leiden University,PO Box 9516, 2300 RA Leiden, The Netherlands.............................................................................................................................................................................Evolutionary developmental biology has encouraged a change ofresearch emphasis from the sorting of phenotypic variation bynatural selection to the production of that variation throughdevelopment1. Some morphologies are more readily generatedthan others, and developmental mechanisms can limit or channelevolutionary change2. Such biases determine how readily popu-lations are able to respond to selection3, and have been postulatedto explain stasis in morphological evolution4and unexploredmorphologies5. There has been much discussion about evolution-ary constraints6–8but empirical data testing them directly aresparse9,10. The spectacular diversity in butterfly wing patterns11issuggestive of how little constrained morphological evolution canbe. However, for wing patterns involving serial repeats of thesame element, developmental properties suggest that some direc-tions of evolutionary change might be restricted12,13. Here weshow that despite the developmental coupling between differenteyespots in the butterfly Bicyclus anynana, there is great potentialfor independent changes. This flexibility is consistent with thediversity of wing patterns across species and argues for adominant role of natural selection, rather than internal con-straints, in shaping existing variation.Figure 1 Response to artificial selection on the size of the dorsal forewing eyespots ofB. anynana. a, Eyespot diameter/wing size relative to unselected control values are givenfor the different directions of selection. AP and ap are coupled directions; Ap and aP areuncoupling directions. Each point represents the mean (^standard error) for the tworeplicate lines for each generation. Solid lines join points covering the first 11 consecutivegenerations, all starting from the same original population (centre of graphic, G0). Brokenlines join the points for G11 and G25 phenotypes. b, Enlargement of the central area of ashowing the behaviour of individual replicate lines (filled and open symbols). c, Typicaldorsal surface of forewing of unselected female showing the anterior (A) and posterior (P)eyespots. d, Representative G25 phenotypes (most ap females have no eyespots andmany AP females have extra, satellite eyespots). Responses in males were comparable tothose in females.letters to natureNATURE | VOL 416 | 25 APRIL2002 | www.nature.com844© 2002 Macmillan Magazines LtdThe different pattern elements on butterfly wings, including