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

Stockholm University, Tukholma, Stockholm, Sweden
Proceedings of the Royal Society B: Biological Sciences (Impact Factor: 5.05). 05/2013; 266:1413-1418. DOI: 10.1098/rspb.1999.0795
Source: PubMed Central


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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    • "However, these ecological associations with the direction of bias have not involved subtle asymmetries, which are thought to arise due to errors made during development. There is a paucity of investigations that move beyond considering these slight departures from symmetry as nonheritable " errors " into considering them as new phenotypes with which to exploit new niche space (but see Seligmann 1998; Windig and Nylin 1999). Such information could identify ecological mechanisms that underlie the fitness and biomechanical consequences of subtle asymmetry in phenotype. "
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    • "Loss of wing area is not the only problem faced by wingworn organisms. Events that cause wing wear, such as failed predator attacks or collisions with solid objects, can result in asymmetric wings, for example in butterflies (Carpenter 1937; Windig and Nylin 1999) and in solitary bees (Mueller and Wolf-Mueller 1993). Asymmetry complicates flight because an individual must compensate for the differential lift and thrust created by each wing. "
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    • "Other potential costs include the risk of sustaining injury and the opportunity cost of lost mate locating time. One persistent suggestion in the literature, based upon the observation that butterfly contests present elaborate aerial manoeuvres, is that flight performance attributes, such as acceleration ability and/or manoeuvrability, may be important determinants of RHP (Baker 1972; Berwaerts et al. 2002; Hernández and Benson 1998; Karlsson 1994; Stjernholm and Karlsson 2000; Wickman 1992; Windig and Nylin 1999). Relative flight performance could prove routinely decisive in aerial wars of attrition if more agile individuals are better able to manage the risk of injury and/ or death (through collision with their opponent, vegetation and other objects, or predatory attack), thus affording them a relatively lower rate of cost accrual. "
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