Modularity, individuality, and evo-devo in butterfly wings

Abstract

Modularity in animal development is thought to have facilitated morphological diversification, but independent change of those traits integrated within a module might be restricted. Correlations among traits describe potential developmental constraints on evolution. These have often been postulated to explain patterns of morphological variation and have been examined theoretically but seldom analyzed experimentally. Here, we use artificial selection to explore the modular organization of butterfly wing patterns and the extent to which their evolution is constrained by the genetic correlations among repeated pattern elements. We show that, in Bicyclus anynana butterflies, despite the evidence that all eyespots are developmentally coupled, the response to selection for increased size of one individual eyespot can proceed in a manner largely independent from selection imposed on another eyespot. We argue that among-eyespot correlations are unlikely to have constrained the evolutionary diversification of butterfly wing patterns but might be important when only limited time is available for adaptive evolution to occur. The ease with which we have been able to produce independent responses to artificial selection on different eyespots may be linked to a legacy of natural selection favoring individuality. Our results are discussed within the context of the evolution of modularity and individuality of serially repeated morphological traits.

Modularity of stress response evolution

“…We also annotated each species as being Gram-positive (47 species) or not, and noted the animal pathogens (117 species), plant pathogens (17 species), strict anaerobes (97 species), and extremophiles (33 species) among the 207 species. Although the eight phenotypes listed should in theory allow for 2 8 ϭ 256 possible combinations (implying that the sample size of 207 species would not even reach saturation), there were only 48 unique combinations of phenotypes, with the five most frequent combinations all being instances of disease-causing motile anaerobes, confirming the well known bias toward sequencing medically relevant intracellular pathogens.…”

“…A modular system builds complexity out of simpler, repurposable units so that a minimum of rewiring among the modules can create entirely new function (1,2). Indeed, modularity has been shown to underlie biological function at the level of transcription (3,4), epistatic interactions (5), protein structure (6,7), and embryonic development (8). Recent studies have examined the degree to which biological networks are modular, catalogued the types and compositions of modules, and traced how they are evolutionarily rewired and tuned by evolution for new function.…”

Diet and hormonal manipulation reveal cryptic genetic variation: implications for the evolution of novel feeding strategies

“…Although the heritability of plasticity can be measured (Laurila et al 2002;Relyea 2005;Gomez-Mestre et al 2008;Talloen et al 2009; electronic supplementary material, appendix S4), it is unclear whether selection acts on reaction norms per se. Indeed, empirical studies have found that plasticity may fail to respond to artificial selection in the presence of genetic variation for the reaction norm (van Kluenen et al 2002) and, conversely, evolve in spite of a strong genetic correlation between traits in alternate environments (Beldade et al 2002;Czesak et al 2006). Some have argued that, as long as genetic variation exists for a trait in each environment, reaction norms will arise as an emergent property of selection favouring different trait optima in different environments (Via & Lande 1985;Via 1993).…”

Evolution of danio pigment pattern development

“…Pattern-generating mechanisms that depend on interactions among pigment cells could be especially significant evolutionarily, if such mechanisms allow patterns to develop in a 'modular' way, largely independent of other traits (Maynard Smith et al, 1985;von Dassow and Munro, 1999;Beldade et al, 2002). New variants could thus arise, and so be available for selection, without correlated alterations in other characters.…”