Article

On the origins of sexual dimorphism in butterflies.

Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06511, USA.
Proceedings of the Royal Society B: Biological Sciences (Impact Factor: 5.68). 12/2010; 278(1714):1981-8. DOI: 10.1098/rspb.2010.2220
Source: PubMed

ABSTRACT The processes governing the evolution of sexual dimorphism provided a foundation for sexual selection theory. Two alternative processes, originally proposed by Darwin and Wallace, differ primarily in the timing of events creating the dimorphism. In the process advocated by Darwin, a novel ornament arises in a single sex, with no temporal separation in the origin and sex-limitation of the novel trait. By contrast, Wallace proposed a process where novel ornaments appear simultaneously in both sexes, but are then converted into sex-limited expression by natural selection acting against showy coloration in one sex. Here, we investigate these alternative modes of sexual dimorphism evolution in a phylogenetic framework and demonstrate that both processes contribute to dimorphic wing patterns in the butterfly genera Bicyclus and Junonia. In some lineages, eyespots and bands arise in a single sex, whereas in other lineages they appear in both sexes but are then lost in one of the sexes. In addition, lineages displaying sexual dimorphism were more likely to become sexually monomorphic than they were to remain dimorphic. This derived monomorphism was either owing to a loss of the ornament ('drab monomorphism') or owing to a gain of the same ornament by the opposite sex ('mutual ornamentation'). Our results demonstrate the necessity of a plurality in theories explaining the evolution of sexual dimorphism within and across taxa. The origins and evolutionary fate of sexual dimorphism are probably influenced by underlying genetic architecture responsible for sex-limited expression and the degree of intralocus sexual conflict. Future comparative and developmental work on sexual dimorphism within and among taxa will provide a better understanding of the biases and constraints governing the evolution of animal sexual dimorphism.

0 Bookmarks
 · 
156 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We evolved violet structural color from brown-colored butterflies over six generations of artificial selection. The mechanism of color generation was identified and found to mimic the natural evolution of violet/blue color in closely related species.
    CLEO: Science and Innovations; 06/2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Sexual differences are often dramatic and widespread across taxa. Their extravagance and ubiquity can be puzzling because the common underlying genome of males and females is expected to impede rather than foster phenotypic divergence. Widespread dimorphism, despite a shared genome, may be more readily explained by considering the multivariate, rather than univariate, framework governing the evolution of sexual dimorphism. In the univariate formulation, differences in genetic variances and a low intersexual genetic correlation (rMF) can facilitate the evolution of sexual dimorphism. However, studies that have analysed sex-specific differences in heritabilities or genetic variances do not always find significant differences. Furthermore, many of the reported estimates of rMF are very high and positive. When monomorphic heritabilities and a high rMF are present together, the evolution of sexual dimorphism on a trait-by-trait basis is severely constrained. By contrast, the multivariate formulation has greater generality and more flexibility. Although the number of multivariate sexual dimorphism studies is low, almost all support sex-specific differences in the G (variance-covariance) matrix; G matrices can differ with respect to size and/or orientation, affecting the response to selection differently between the sexes. Second, whereas positive values of the univariate quantity rMF only hinder positive changes in sexual dimorphism, positive covariances in the intersexual covariance B matrix can either help or hinder. Similarly, the handful of studies reporting B matrices indicate that it is often asymmetric, so that B can affect the evolution of single traits differently between the sexes. Multivariate approaches typically demonstrate that genetic covariances among traits can strongly constrain trait evolution when compared with univariate approaches. By contrast, in the evolution of sexual dimorphism, a multivariate view potentially reveals more opportunities for sexual dimorphism to evolve by considering the effect sex-specific selection has on sex-specific G matrices and an asymmetric B matrix.
    Journal of Evolutionary Biology 10/2013; 26(10):2070-80. · 3.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Evo-devo seeks to explain the origins of novelties in terms of genetics. Butterfly eyespots offer a fertile subfield for such investigations. Previous explanations for the origin of eyespots are reviewed, and a new hypothesis is presented. According to this new “Recursion Model,” eyespots are ectopic versions of the wing margin. Evidence for this equivalence includes: (1) secretion of the morphogen Wingless, (2) expression of the homeobox gene Distal-less, and (3) specification of outlying contours that take the form of stripes or rings. These three steps constitute a modular program that was initially executed only at the margin. The model proposes that eyespots were created when the program was accidentally rebooted (recursively) at certain points in the wing blade by a fortuitous mutation that occurred at the dawn of the Nymphalid family. Those points are located wherever two interacting genes are expressed. Gene A is expressed midway between adjacent wing veins, while gene B is expressed at a certain distance from the wing margin. The mutation is thought to have installed a new cis-enhancer at the wingless gene locus, which was uniquely responsive to the combination of A and B inputs. Because the postulated enhancer should be easy to pinpoint by transgenic in vivo assays of reporter constructs, this new model is directly testable. If it proves correct, then eyespots would become one of only a few putative cases where a novel feature arose suddenly.
    Evolutionary Biology 40(1). · 2.39 Impact Factor

Full-text (2 Sources)

View
46 Downloads
Available from
Jun 1, 2014