Female choice depends on size but not symmetry of dorsal eyespots in the butterfly Bicyclus anynana.

The eyespots on the ventral wings of Bicyclus anynana butterflies are exposed when at rest and interact with predators. Those on the dorsal surface are not exposed in this way, and may be involved in courtship and mate choice. In this study, we examined whether the size and fluctuating asymmetry (FA) of dorsal eyespots are reliable signals of male quality. High developmental stability is considered to result in low FA, and to be associated with high quality. Individuals of high quality are predicted to produce sexually selected traits that are large and symmetrical, at a relatively low cost. In this study, we manipulated eyespot development to uncouple eyespot size and FA in order to examine their independent roles in signalling to the female. Individual females in cages were given the choice between two or three males differing in eyespot traits. The results indicate that although size per se of the eyespots is used as a signal, FA and wing size are not. We discuss the use of FA in studies of sexual selection and aspects of sexual selection on dorsal eyespot size.

Breuker CJ ，Brakefield PM 《-》

Female Bicyclus anynana butterflies choose males on the basis of their dorsal UV-reflective eyespot pupils.

Sexual and natural selection pressures are thought to shape the characteristic wing patterns of butterfly species. Here we test whether sexual selection by female choice plays a role in the maintenance of the male wing pattern in the butterfly Bicyclus anynana. We perform one of the most extensive series of wing pattern manipulations in butterflies, dissecting every component of the 'bulls-eye' eyespot patterns in both ventral and dorsal wing surfaces of males to test the trait's appeal to females. We conclude that females select males on the basis of the size and brightness of the dorsal eyespot's ultraviolet reflecting pupils. Pupil absence is strongly selected against, as are artificially enlarged pupils. Small to intermediate (normal sized) pupils seem to function equally well. This work contradicts earlier experiments that suggest that the size of dorsal eyespots plays a role in female choice and explains why male dorsal eyespots are very variable in size and often have indistinct rings of coloration, as the only feature under selection by females seems to be the central white pupil. We propose that sexual selection by female choice, rather than predator avoidance, may have been an important selective factor in the early stages of eyespot evolution in ancestral Lepidopteran lineages.

Robertson KA ，Monteiro A 《-》

Male Bicyclus anynana Butterflies Choose Females on the Basis of Their Ventral UV-Reflective Eyespot Centers.

Butterflies often use their dorsal and ventral wing color patterns for distinct signaling functions. Color patterns on hidden dorsal wing surfaces are often used in sexual signaling, while exposed ventral patterns are often used to ward off predator attacks. At rest, however, part of the ventral forewings are often hidden by the hindwings, allowing individuals to also use the patterns on this wing surface for sexual signaling. Here, we test this hypothesis in Bicyclus anynana (Butler, Lepidoptera, Nymphalidae) butterflies by first determining the degree of sexual dimorphism in ventral forewing patterns, focusing on the eyespots, from both wet and dry season forms, and then testing the role of the larger ventral forewing eyespots of dry season females in male mate choice. We also test male investment in reproduction. We show that ventral forewing UV-reflective eyespot centers, in addition to dorsal forewing eyespot centers previously examined in this species, play a role in sexual signaling as males preferentially mated with females with their ventral eyespot centers intact instead of blocked with black paint. This male preference, however, did not translate into a detectable higher reproductive investment via a single mating toward ornamented females. This study provides an example of how ventral forewing patterns, often hidden by hindwings, are used in sexual communication, in this case by females to attract males.

Huq M ，Bhardwaj S ，Monteiro A 《JOURNAL OF INSECT SCIENCE》

Heat shock in the developmentally sensitive period of butterfly eyespots fails to increase fluctuating asymmetry.

Fluctuating asymmetry (FA) is considered to provide a means of evaluating developmental stability and to reflect an individual's quality or the stress experienced during development. Stress is predicted to increase the phenotypic variation of both FA and trait size. In this study we examined the effect of a particular heat shock on both FA and size of eyespots in the butterfly, Bicyclus anynana. We also examined whether those eyespots thought to be involved in partner choice and sexual selection were particularly sensitive to stress. We applied a heat shock of 39.5 degrees C for 3 h before, during, and after a sensitive period in eyespot development. We examined the FA, variation in FA, size, and variation in size of five eyespots, two on the dorsal forewing (sexually selected traits), two on the ventral forewing, and one on the ventral hindwing (nonsexually selected traits). For each sex and treatment, the heat shock did not result in significant changes in mean trait size and FA nor in the variation of size and FA. There were no differences in the response to the heat shock between sexually and nonsexually selected traits. We discuss how the increased production of heat shock proteins, including HSP60, may have stabilized development and how this might explain the results.

Breuker CJ ，Brakefield PM 《EVOLUTION & DEVELOPMENT》

Does predation maintain eyespot plasticity in Bicyclus anynana?

The butterfly Bicyclus anynana exhibits phenotypic plasticity involving the wet-season phenotype, which possesses marginal eyespots on the ventral surface of the wings, and the dry-season form, which lacks these eyespots. We examined the adaptive value of phenotypic plasticity of B. anynana in relation to the defence mechanisms of crypsis and deflection. We assessed the visibility differences between spotless and spotted butterflies against backgrounds of brown (dry season) or green (wet season) leaves. Spotless butterflies were highly cryptic and less predated by adult bird predators than were spotted ones when presented against brown leaf litter. However, the advantage of crypsis disappeared in the wet-season habitat as both forms were equally visible. In later experiments, naive birds presented with resting butterflies in the wet-season habitat tended to learn more rapidly to capture spotless butterflies, suggesting a slight selective advantage of possessing eyespots. Moreover, marginal eyespots increased significantly the escape probability of butterflies that were attacked by naive birds compared to those attacked by adult birds, although there were no differences in prey capture success within naive predators. Our results show that natural selection acts against eyespots in the dry season, favouring crypsis, whereas in the wet season it may favour eyespots as deflective patterns.

Lyytinen A ，Brakefield PM ，Lindström L ，Mappes J ... -  《-》