Abstract
Butterfly eyespots are complex morphological traits that can vary in size, shape and color composition even on the same wing surface. Homology among eyespots suggests they share a common developmental basis and function as an integrated unit in response to selection. Despite strong evidence of genetic integration, eyespots can also exhibit modularity or plasticity, indicating an underlying flexibility in pattern development. The extent to which particular eyespots or eyespot color elements exhibit modularity or integration is poorly understood, particularly following exposure to novel conditions. We used perturbation experiments to explore phenotypic correlations among different eyespots and their color elements on the ventral hindwing of V. cardui. Specifically, we identified which eyespots and eyespot features are most sensitive to perturbation by heat shock and injection of heparin—a cold shock mimic. For both treatments, the two central eyespots (3 + 4) were most affected by the experimental perturbations, whereas the outer eyespot border was more resistant to modification than the interior color elements. Overall, the individual color elements displayed a similar response to heat shock across all eyespots, but varied in their response to each other. Graphical modeling also revealed that although eyespots differ morphologically, regulation of eyespot size and colored elements appear to be largely integrated across the wing. Patterns of integration, however, were disrupted following heat shock, revealing that the strength of integration varies across the wing and is strongest between the two central eyespots. These findings support previous observations that document coupling between eyespots 3 + 4 in other nymphalid butterflies.
Highlights
Eyespots are one of the most striking and diverse features displayed on butterfly wings
We explore patterns of integration and modularity in the globally distributed butterfly, Vanessa cardui (Nymphalidae) by investigating how individual eyespots and their corresponding color elements respond to two different physiological perturbations, heat shock and heparin
Caterpillars arrived as 2nd instar larvae and were randomly assigned to the following treatment groups: heat shock, heparin injection or control
Summary
Eyespots are one of the most striking and diverse features displayed on butterfly wings. These colorful pattern elements are composed of concentric rings or pattern elements that can vary widely in size, number and color composition even on the same wing surface. WR was supported through the National Science Foundation (http://www.nsf.gov/funding/pgm_summ.jsp?pims_id= 5517&from=fund) Research Experience for Undergraduates Grant 0851869 and by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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