Ecological genetics of color and life history characters in an aposematic ladybird beetle.

摘要

Color has been long recognized as an important component of animal ecology. Recent advances in the measurement and analysis of color patterns have made more detailed and precise approaches to the study of color feasible. I use a combination of ecological, quantitative genetic, and spectrometric experiments to investigate the role of color in the ecology of the aposematic ladybird beetle, Harmonia axyridis.;I use state-of-the-art spectrometry equipment to assess whether or not estimates of the component parts of a color signal (brightness, chroma, and hue) based on principle component analysis of reflectance curves accurately reflect actual values for those components in standardized Munsell color samples. I further compared these results to those obtained using a different technique, segment classification, to assess which was most effective under several color conditions. Principal component analysis appeared to be the superior method, especially when colors were primarily reddish in hue. Other color analysis techniques are also examined.;I next examined the relationships between color and other important characters in Harmonia. Intermittent use of an antipredator tactic suggests that the tactic is costly and thus, expression occurs only when it is perceived as necessary. I investigated effects of reflex bleeding, a chemical defense tactic in ladybirds, on expression of life history and color characters. I hypothesized that repeated use of reflex bleeding should result in diminished performance in life history characters and result in a reduction in the intensity of red beetle coloration. These reflex bleeding treatments were augmented with studies on diet treatments to investigate the role of interactive effects between environmental quality and use of chemical defense. Adult size and color were affected by reflex bleeding in some, but not all, cases. Quality of diet was found to affect all traits measured, regardless of application of a reflex bleeding treatment.;Separate studies of diet were executed to assess the role of environmental quality on expression of life history and morphological characters, correlations between characters, genetic constraints to evolution, and heritability of key characters in different environments. Again, diet affected expression of all characters to a substantial degree. In addition, quantitative genetic parameter estimates depended on the environment in which characters were expressed, especially for life history characters.;Finally, I investigated the role of juvenile and adult environmental quality in influencing the development of adult elytron, or wing-covering, color. Adults continue to develop brighter and darker coloration for many weeks after eclosion. I predicted that exposure to the lower quality environment would reduce the brightness and redness of the adults. Diet in the adult stage was shown to influence development of color, but neither juvenile diet nor induction of reflex bleeding in either the juvenile or adult stage had any effects on development of color in adults.