Adaptive wing asymmetry in males of the speckled wood butterfly (Pararge aegeria)?

Proceedings of the Royal Society B: Biological Sciences (Impact Factor: 5.29). 05/2013; 266:1413-1418. DOI: 10.1098/rspb.1999.0795
Source: PubMed Central

ABSTRACT We analysed asymmetry in the wings of the speckled wood butterfly (Pararge aegeria)by measuring area, length and width of fore- and hindwings. The type of asymmetry is fluctuating except for fore- and hindwing area, and forewing width in males, where asymmetry is directional. The amount of asymmetry (variance of the left wing minus the right wing) is less in males than in females. Within males asymmetry was directional and less in pale, predominantly territorial males than in melanic, predominantly non-territorial males. Asymmetry was negatively related to growth rate within females, but not within males. Females grew faster than males, but had higher asymmetry, whereas the more asymmetrical melanic males grew more slowly than pale males. The differences in the type and amount of asymmetry between the sexes and colour classes suggest a relationship with sex-specific flight patterns such as the territorial spiralling flight of males. We hypothesize that slightly asymmetrical males turn faster, and therefore are superior in territorial disputes over more symmetrical or extremely asymmetrical males. This implies that sexual selection via male–male competition influences the type and amount of asymmetry. The existence of more extremely asymmetrical individuals in females, and to a lesser extent in non-territorial males, may indicate that there are costs in reducing asymmetry.

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    ABSTRACT: Directional asymmetry (DA) has received considerably less attention than fluctuating asymmetry (FA) in the literature. Evidence for DA, however, is building among insect taxa. We examined asymmetries in two wing traits within both sexes of the damselfly Calopteryx maculata (Beauvois) (Odonata: Calopterygidae) sampled from three sites in southeastern Ontario. After accounting for measurement error, we show that proximal segments within right fore and hind wings are consistently longer than those in the left in all but one sample group. Full wing lengths, however, exhibited FA rather than DA. Mean asymmetry values for both traits (segment and length) occurred in the direction of right-wingedness significantly more often than expected by chance. Patterns of asymmetry were generally consistent among the sexes and sites, although males tended to exhibit more pronounced DA. We suggest that the wings of C. maculata may undergo compensatory development, so that full lengths are more bilaterally symmetrical than their component parts. Résumé : L'asymétrie directionnelle (DA) est un phénomène beaucoup moins étudié que l'asymétrie fluctuante (FA) dans la littérature. Cependant, nous avons de plus en plus de preuves que l'asymétrie directionnelle prévaut chez les in-sectes. Nous avons étudié l'asymétrie de deux caractéristiques des ailes chez des mâles et des femelles de la Demoi-selle bistrée, Calopteryx maculata (Beauvois) (Odonata : Calopterygidae) échantillonnés à trois endroits dams le sud-est de l'Ontario. En tenant compte des erreurs de mesures, nous avons constaté que les segments proximaux des ailes anté-rieure et postérieure droites étaient toujours plus longs que dans les ailes de gauche, chez tous les groupes échantillon-nés sauf un. La longueur totale des ailes, toutefois, subit une asymétrie fluctuante plutôt que directionnelle. Les valeurs moyennes de l'asymétrie dans les deux cas (segments et longueur totale) tendent a favoriser l'aile droite significative-ment plus souvent que si elles étaient dues au hasard. L'asymétrie est généralement semblable chez les deux sexes et à tous les sites, mais les mâles font preuve d'une asymétrie directionnelle plus importante. Il est possible que les ailes de C. maculata subissent un développement de compensation qui fait que la longueur totale a une symétrie bilatérale plus importante que les composantes des ailes.
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