Flavonoid wing pigments increase attractiveness of female common blue (Polyommatus icarus) butterflies to mate-searching males.

Common blue butterflies (Polyommatus icarus) sequester flavonoids from their larval host plants and allocate these UV-absorbing pigments to the wings. In field experiments using dummies constructed from female butterflies, mate-searching males inspected flavonoid-rich dummies more intensively than those with little or no flavonoids. Flavonoid content as signalled by UV-wing pattern may indicate ontogenetically determined female quality or enhance detectability to males.

Burghardt F ，Knüttel H ，Becker M ，Fiedler K ... -  《Science of Nature》

Host-plant-derived variation in ultraviolet wing patterns influences mate selection by male butterflies.

We report on the first case in which sequestered secondary plant compounds determine an insect's external appearance in the ultraviolet spectrum and thereby influence visually mediated mate choice. Larvae of the common blue butterfly Polyommatus icarus specifically sequester flavonoids in different amounts and types, depending on the part or species of food plant. During late pupal development the majority of ultraviolet-absorbing flavonoids are deposited in the wing scales. The flavonoid content of the larval diet thereby determines ultraviolet wing patterns. In laboratory and field experiments, male butterflies clearly preferred flavonoid-rich, ultraviolet-absorbing female dummies. This preference is mediated visually by the ultraviolet pattern of the wings. Food-plant parts and species vary in value as a food source, so ultraviolet wing patterns may signal mate quality and are not a species-specific characteristic. We discuss the use of principal component analysis in analysing spectral data in the context of visual communication. We propose the alternative application of confidence intervals of averaged spectra as a novel straightforward statistical method for comparing groups of spectra in a manner that is independent of assumptions about the visual system of the receiver. In addition, they can be used to give confidence intervals to derived measures of colour such as quantum catch by photoreceptors.

Knüttel H ，Fiedler K 《JOURNAL OF EXPERIMENTAL BIOLOGY》

Flavonoid sequestration by the common blue butterfly Polyommatus icarus: quantitative intraspecific variation in relation to larval hostplant, sex and body size.

Common blue butterflies (Polyommatus icarus) sequester flavonoids from their larval food and store these pigments as part of their adult wing colouration. Insects were reared on 10 different diets to assess effects of host plants on variation in flavonoid sequestration in this moderately polyphagous butterfly. Rearing experiments revealed an unexpectedly large gradient in flavonoid richness, ranging from individuals with high flavonoid loads (reared on inflorescences of Medicago sativa, Trifolium repens, T. pratense) to butterflies which contained almost no such pigments (fed with foliage of M. sativa or Robinia pseudoacacia). Flavonoid sequestration was much more effective from natural hostplants than from experimentally offered diets which would not be accepted in the field. Female butterflies on average sequestered almost 60% more flavonoids than males. This sex difference was more pronounced on natural than on experimental diets. Flavonoid load was significantly and positively related to dry mass and forewing length as two important fitness correlates of butterflies. This correlation was particularly strong on experimental diets (i.e. under constraining conditions for development). On natural hostplants, in contrast, when butterflies generally were flavonoid-rich, no clear relationship between flavonoid load and size or mass emerged. Our analytical data are consistent with field results according to which females rich in UV-absorbing flavonoid wing pigments are more attractive to mate-searching males. In P. icarus, flavonoid richness might therefore increase visibility (by more effective sensory stimulation of the visual system), but could also confer information about the feeding history, and thus ontogenetically determined 'quality' of a potential mate.

Burghardt F ，Proksch P ，Fiedler K 《BIOCHEMICAL SYSTEMATICS AND ECOLOGY》

The evolution of wing color: male mate choice opposes adaptive wing color divergence in Colias butterflies.

Correlated evolution of mate signals and mate preference may be constrained if selection pressures acting on mate preference differ from those acting on mate signals. In particular, opposing selection pressures may act on mate preference and signals when traits have sexual as well as nonsexual functions. In the butterfly Colias philodice eriphyle, divergent selection on wing color across an elevational gradient in response to the thermal environment has led to increasing wing melanization at higher elevations. Wing color is also a long-range signal used by males in mate searching. We conducted experiments to test whether sexual selection on wing melanization via male mate choice acts in the same direction as natural selection on mate signals due to the thermal environment. We performed controlled mate choice experiments in the field over an elevational range of 1500 meters using decoy butterflies with different melanization levels. Also, we obtained a more direct estimate of the relation between wing color and sexual selection by measuring mating success in wild-caught females. Both our experiments showed that wing melanization is an important determinant of female mating success in C. p. eriphyle. However, a lack of elevational variation in male mate preference prevents coevolution of mate signals and mate preference, as males at all elevations prefer less-melanized females. We suggest that this apparently maladaptive mate choice may be maintained by differences in detectability between the morphs or by preservation of species recognition.

Ellers J ，Boggs CL 《EVOLUTION》

Changes in structural and pigmentary colours in response to cold stress in Polyommatus icarus butterflies.

While numerous papers have investigated the effects of thermal stress on the pigmentary colours of butterfly wings, such studies regarding structural colours are mostly lacking, despite the important role they play in sexual communication. To gain insight into the possible differences between the responses of the two kinds of colouration, we investigated the effects of prolonged cold stress (cooling at 5 °C for up to 62 days) on the pupae of Polyommatus icarus butterflies. The wing surfaces coloured by photonic crystal-type nanoarchitectures (dorsal) and by pigments (ventral) showed markedly different behaviours. The ventral wing surfaces exhibited stress responses proportional in magnitude to the duration of cooling and showed the same trend for all individuals, irrespective of their sex. On the dorsal wing surface of the males, with blue structural colouration, a smaller magnitude response was found with much more pronounced individual variations, possibly revealing hidden genetic variations. Despite the typical, pigmented brown colour of the dorsal wing surface of the females, all cooled females exhibited a certain degree of blue colouration. UV-VIS spectroscopy, optical microscopy, and scanning and transmission electron microscopy were used to evaluate the magnitude and character of the changes induced by the prolonged cold stress.

Kertész K ，Piszter G ，Horváth ZE ，Bálint Z ，Biró LP ... -  《Scientific Reports》