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The visual systems and diel activity patterns of butterflies and moths have been studied for decades, yet understanding the underlying mechanisms that are associated with the evolution of these remains a major challenge. The order Lepidoptera is principally composed of nocturnal lineages with extreme morphological and behavioural adaptations to this lifestyle. Although most butterflies are diurnal, some clades are predominantly nocturnal, for instance, the Hedylidae. Skippers are another family that comprises multiple crepuscular and/or nocturnal lineages. Interestingly, many such lineages have red-eye pigmentation, and this morphological feature has been hypothesised to be an adaptation to the night-time lifestyle. Here, we review the occurrence and frequency of red-eye pigmentation as well as diel activity patterns in Hesperiidae. We place these data within a phylogenomic framework and provide hypotheses and predictions relative to the evolution of red-eye pigmentation in skippers with respect to diel activity. We suggest that several types of red-eye pigmentation exist in skippers, with possible structural red-eye pigmentation in some lineages of diurnal skippers. The colouration of eyes in Hesperiidae, the evolutionary mechanisms that drive these traits and the physiological underlying processes require further attention and could bring new insights into our understanding of butterfly vision systems. [ABSTRACT FROM AUTHOR]

Adaptive coloration is under conflicting selection pressures: choosing potential mates and warning signaling against visually guided predators. Different elements of the color signal may therefore be tuned by evolution for different functions. We investigated how mimicry in four pairs of Heliconius comimics is potentially seen both from the perspective of butterflies and birds. Visual sensitivities of eight candidate avian predators were predicted through genetic analysis of their opsin genes. Using digital image color analysis, combined with bird and butterfly visual system models, we explored how predators and conspecifics may visualize mimetic patterns. Ultraviolet vision (UVS) birds are able to discriminate between the yellow and white colors of comimics better than violet vision (VS) birds. For Heliconius vision, males and females differ in their ability to discriminate comimics. Female vision and red filtering pigments have a significant effect on the perception of the yellow forewing band and the red ventral forewing pattern. A behavioral experiment showed that UV cues are used in mating behavior; removal of such cues was associated with an increased tendency to approach comimics as compared to conspecifics. We have therefore shown that visual signals can act to both reduce the cost of confusion in courtship and maintain the advantages of mimicry. [ABSTRACT FROM AUTHOR]

The Australian lycaenid butterfly Jalmenus evagoras has iridescent wings that are sexually dimorphic, spectrally and in their degree of polarization, suggesting that these properties are likely to be important in mate recognition. We first describe the results of a field experiment showing that free-flying individuals of J. evagoras discriminate between visual stimuli that vary in polarization content in blue wavelengths but not in others. We then present detailed reflectance spectrophotometry measurements of the polarization content of male and female wings, showing that female wings exhibit blue-shifted reflectance, with a lower degree of polarization relative to male wings. Finally, we describe a novel method for measuring alignment of ommatidial arrays: by measuring variation of depolarized eyeshine intensity from patches of ommatidia as a function of eye rotation, we show that (a) individual rhabdoms contain mutually perpendicular microvilli; (b) many rhabdoms in the array have their microvilli misaligned with respect to neighboring rhabdoms by as much as 45 deg; and (c) the misaligned ommatidia are useful for robust polarization detection. By mapping the distribution of the ommatidial misalignments in eye patches of J. evagoras, we show that males and females exhibit differences in the extent to which ommatidia are aligned. Both the number of misaligned ommatidia suitable for robust polarization detection and the number of aligned ommatidia suitable for edge detection vary with respect to both sex and eye patch elevation. Thus, J. evagoras exhibits finely tuned ommatidial arrays suitable for perception of polarized signals, likely to match sex-specific life history differences in the utility of polarized signals., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

Because of the important role sensory systems play in the behaviour of animals, information on sensory capabilities is of great value to behavioural ecologists in the development of hypotheses to explain behaviour. In compound eyes, interommatidial angles are a key determinant of visual acuity but methods for measuring these angles are often demanding and limited to live animals with a pseudopupil. Here we present a new technique for measuring interommatidial angles that is less demanding in terms of technology than other techniques but still accurate. It allows measurements in eyes without a pseudopupil such as dark eyes or even museum specimens. We call this technique the radius of curvature estimation ( RCE) method. We describe RCE and validate the method by comparing results from RCE with those from pseudopupil analysis for the butterfly Asterocampa leilia. As an application of RCE we measure the eyes of the butterfly Battus philenor, a species whose visually guided behaviour is well known but whose eye structure and visual acuity are unknown. We discuss the results of the eye morphology in B. philenor in relation to their behaviour and ecology. We contend that RCE fills a gap in the repertoire of techniques available to study peripheral determinants of spatial resolution in compound eyes, because it can be applied on species with dark eyes. RCE then opens up for sampling a larger number of specimens, which, in combination with being able to use museum specimens, makes it possible to quantitatively test ecologically and evolutionarily driven hypotheses about vision in animals in a new way. [ABSTRACT FROM AUTHOR]

The eyes of the Japanese yellow swallowtail butterfly, Papilio xuthus, contain six spectral classes of photoreceptors, each sensitive either in the ultraviolet, violet, blue, green, red or broadband wavelength regions. The green-sensitive receptors can be divided into two subtypes, distal and proximal. Previous behavioral and anatomical studies have indicated that the distal subtype appears to be involved in motion vision, while the proximal subtype is important for color vision. Here, we studied the dynamic properties of Papilio photoreceptors using light stimulation with randomly modulated intensity and light pulses. Frequency response (gain) of all photoreceptor classes shared a general profile-a broad peak around 10 Hz with a declining slope towards higher frequency range. At 100 Hz, the mean relative gain of the distal green receptors was significantly larger than any other receptor classes, indicating that they are the fastest. Photoreceptor activities under dim light were higher in the ultraviolet and violet receptors, suggesting higher transduction sensitivities. Responses to pulse stimuli also distinguished the green receptors from others by their shorter response latencies. We thus concluded that the distal green receptors carry high frequency information in the visual system of Papilio xuthus. [ABSTRACT FROM AUTHOR]

Territory residency is associated with considerable benefits. In the speckled wood butterfly, Pararge aegeria, males fight over ownership of large sunspots in open forest habitats; winners become sunspot residents, and losers become nonterritorial and sit and wait for females in small sunspots. A previous study has shown that residents have higher mating success than nonterritorial males, although females are not more attracted to territorial males or sunspot territories per se. Here we tested the hypotheses (1) that the higher success of resident males is caused by visual mate detection being more efficient in a large than in a small sunspot, and (2) that only sunspots above a certain size are defended as territories. Field assessment of territorial sunspot size showed that defended sunspots were significantly larger than ‘average sunspots’ on the forest floor. Experimental tests of male ability to detect visually a model butterfly passing through a sunspot showed that males were more successful in pursuing and intercepting a passing model when flown a longer distance in the sunspot. Hence, we conclude that light conditions and associated visual mate detection and ability to complete mate flight pursuit can explain why P. aegeria males defend territories in large sunspots in forest habitats. [Copyright &y& Elsevier]

Male Empress Leilia butterflies (Asterocampa leilia) use a sit-and-wait tactic to locate mates. To see how vision might influence male behavior, we studied the morphology, optics, and receptor physiology of their eyes and found the following. (1) Each eye's visual field is approximately hemispherical with at most a 10° overlap in the fields of the eyes. There are no large sexual differences in visual field dimensions. (2) In both sexes, rhabdoms in the frontal and dorsal ommatidia are longer than those in other eye regions. (3) Interommatidial angles are smallest frontally and around the equator of the eye. Minimum interommatidial angles are 0.9–1° in males and 1.3–1.4° in females. (4) Acceptance angles of ommatidia closely match interommatidial angles in the frontal region of the eye. We conclude that vision in these butterflies is mostly monocular and that males have more acute vision than females, especially in the frontal region (large facets, small interommatidial angles, small acceptance angles, long rhabdoms, and a close match between interommatidial angles and acceptance angles). This study also suggests that perched males direct their most acute vision where females are likely to appear but show no eye modifications that appear clearly related to a mate-locating tactic. [ABSTRACT FROM AUTHOR]