Automatic recognition and measurement of butterfly eyespot patterns.

A favorite wing pattern element in butterflies that has been the focus of intense study in evolutionary and developmental biology, as well as in behavioral ecology, is the eyespot. Because the pace of research on these bull's eye patterns is accelerating we sought to develop a tool to automatically detect and measure butterfly eyespot patterns in digital images of the wings. We used a machine learning algorithm with features based on circularity and symmetry to detect eyespots on the images. The algorithm is first trained with examples from a database of images with two different labels (eyespot and non-eyespot), and subsequently is able to provide classification for a new image. After an eyespot is detected the radius measurements of its color rings are performed by a 1D Hough Transform which corresponds to histogramming. We trained software to recognize eyespot patterns of the nymphalid butterfly Bicyclus anynana but eyespots of other butterfly species were also successfully detected by the software.

Silveira M ，Monteiro A 《-》

Developmental and genetic mechanisms for evolutionary diversification of serial repeats: eyespot size in Bicyclus anynana butterflies.

Serially repeated pattern elements on butterfly wings offer the opportunity for integrating genetic, developmental, and functional aspects towards understanding morphological diversification and the evolution of individuality. We use captive populations of Bicyclus anynana butterflies, an emerging model in evolutionary developmental biology, to explore the genetic and developmental basis of compartmentalized changes in eyespot patterns. There is much variation for different aspects of eyespot morphology, and knowledge about the genetic pathways and developmental processes involved in eyespot formation. Also, despite the strong correlations across all eyespots in one butterfly, B. anynana shows great potential for independent changes in the size of individual eyespots. It is, however, unclear to what extent the genetic and developmental processes underlying eyespot formation change in a localized manner to enable such individualization. We use micromanipulations of developing wings to dissect the contribution of different components of eyespot development to quantitative differences in eyespot size on one wing surface. Reciprocal transplants of presumptive eyespot foci between artificial selection lines and controls suggest that while localized antagonistic changes in eyespot size rely mostly on localized changes in focal signal strength, concerted changes depend greatly on epidermal response sensitivities. This potentially reflects differences between the signal-response components of eyespot formation in the degrees of compartmentalization and/or the temporal pattern of selection. We also report on the phenotypic analysis of a number of mutant stocks demonstrating how single alleles can affect different eyespots in concert or independently, and thus contribute to the individualization of serially repeated traits.

Beldade P ，French V ，Brakefield PM 《-》

A simulation study of the genetic regulatory hierarchy for butterfly eyespot focus determination.

The color patterns on the wings of butterflies have been an important model system in evolutionary developmental biology. Two types of models have been used to study these patterns. The first type of model employs computational techniques and generalized mechanisms of pattern formation to make predictions about how color patterns will vary as parameters of the model are changed. These generalized mechanisms include diffusion gradient, reaction-diffusion, lateral inhibition, and threshold responses. The second type of model uses known genetic interactions from Drosophila melanogaster and patterns of candidate gene expression in one of several butterfly species (most often Junonia (Precis) coenia or Bicyclus anynana) to propose specific genetic regulatory hierarchies that appear to be involved in color pattern formation. This study combines these two approaches using computational techniques to test proposed genetic regulatory hierarchies for the determination of butterfly eyespot foci (also known as border ocelli foci). Two computer programs, STELLA 8.1 and Delphi 2.0, were used to simulate the determination of eyespot foci. Both programs revealed weaknesses in a genetic model previously proposed for eyespot focus determination. On the basis of these simulations, we propose two revised models for eyespot focus determination and identify components of the genetic regulatory hierarchy that are particularly sensitive to changes in model parameter values. These components may play a key role in the evolution of butterfly eyespots. Simulations like these may be useful tools for the study of other evolutionary developmental model systems and reveal similar sensitive components of the relevant genetic regulatory hierarchies.

Evans TM ，Marcus JM 《EVOLUTION & DEVELOPMENT》

The "eyespot module" and eyespots as modules: development, evolution, and integration of a complex phenotype.

Organisms are inherently modular, yet modules also evolve in response to selection for functional integration or functional specialization of traits. For serially repeated homologous traits, there is a clear expectation that selection on the function of individual traits will reduce the integration between traits and subdivide a single ancestral module. The eyespots on butterfly wings are one example of serially repeated morphological traits that share a common developmental mechanism but are subject to natural and sexual selection for divergent functions. Here, I test two hypotheses about the organization of the eyespot pattern into independent dorsal-ventral and anterior-posterior modules, using a graphical modeling technique to examine patterns of eyespot covariation among and within wing surfaces in the butterfly Bicyclus anynana. Although there is a hierarchical and complex pattern of integration among eyespots, the results show a surprising mismatch between patterns of eyespot integration and the developmental and evolutionary eyespot units identified in previous empirical studies. These results are discussed in light of the relationships between developmental, functional, and evolutionary modules, and they suggest that developmental sources of independent trait variation are often masked by developmental sources of trait integration.

Allen CE 《-》

Structure of a character and the evolution of butterfly eyespot patterns.

All butterfly eyespots appear to be formed by a similar developmental mechanism. Thus the great diversity of patterns observed across different species of butterfly has evolved through changes in the genetic modulation of this mechanism. Our descriptions of both the development of eyespots and the genetic variation for eyespot traits in an African butterfly, Bicyclus anynana, are used here to discuss the most appropriate ways of applying the character concept to the evolution of butterfly eyespot patterns. J. Exp. Zool. (Mol. Dev. Evol.) 291:93-104, 2001.

Brakefield PM 《-》