Rapid Divergence of Wing Volatile Profiles Between Subspecies of the Butterfly Pieris rapae (Lepidoptera: Pieridae)

Complex signaling traits such as pheromone profiles can play an important role in the early stages of reproductive isolation between populations. These signals can diverge along multiple trait axes, and signal receivers are often sensitive to subtle differences in signal properties. In the Lepidoptera, prior research has highlighted that natural selection can drive rapid chemical signal divergence, for instance via mate recognition to maintain species boundaries. Much less is known about the occurrence of such changes for predominantly sexually selected chemical signals, such as those released by many male lepidopterans. We evaluated the divergence in male and female wing volatile profiles between two recently isolated subspecies of the pierid butterfly Pieris rapae Linnaeus (Lepidoptera: Pieridae): P. rapae rapae and P. rapae crucivora. In laboratory settings, these subspecies exhibit strong premating isolation, with females rejecting males of the opposite subspecies despite the fact that males direct equivalent courtship effort toward females of either subspecies. Using gas chromatography–mass spectrometry, we analyzed the volatile chemical profiles of individual males and females of each subspecies. We find that males of each subspecies differ in their wing volatile profiles, including quantitative differences in a male sex pheromone, ferrulactone. In contrast, female wing volatiles profiles have diverged significantly less. These sexspecific patterns suggest that male chemical profiles may play a role in the observed premating isolation between these two subspecies, providing support for future investigations of sexually selected chemical traits in population divergence

Floral Color Properties of Serpentine Seep Assemblages Depend on Community Size and Species Richness

Functional traits, particularly those that impact fitness, can shape the ecological and evolutionary relationships among coexisting species of the same trophic level. Thus, examining these traits and properties of their distributions (underdispersion, overdispersion) within communities can provide insights into key ecological interactions (e.g., competition, facilitation) involved in community assembly. For instance, the distribution of floral colors in a community may reflect pollinator-mediated interactions between sympatric plant species, and the phylogenetic distribution of color can inform how evolutionary contingencies can continue to shape extant community assemblages. Additionally, the abundance and species richness of the local habitat may influence the type or strength of ecological interactions among co-occurring species. To evaluate the impact of community size and species richness on mechanisms shaping the distribution of ecologically relevant traits, we examined how floral color (defined by pollinator color vision models) is distributed within co-flowering assemblages. We modeled floral reflectance spectra of 55 co-flowering species using honeybee (Apis mellifera) and syrphid fly (Eristalis tenax) visual systems to assess the distributions of flower color across 14 serpentine seep communities in California. We found that phylogenetic relatedness had little impact on the observed color assemblages. However, smaller seep communities with lower species richness were more overdispersed for flower color than larger, more species-rich communities. Results support that competitive exclusion could be a dominant process shaping the species richness of flower color in smaller-sized communities with lower species richness, but this is less detectable or overwhelmed by other processes at larger, more speciose communities

Unprecedented reorganization of holocentric chromosomes provides insights into the enigma of lepidopteran chromosome evolution

Chromosome evolution presents an enigma in the mega-diverse Lepidoptera. Most species exhibit constrained chromosome evolution with nearly identical haploid chromosome counts and chromosome-level gene collinearity among species more than 140 million years divergent. However, a few species possess radically inflated chromosomal counts due to extensive fission and fusion events. To address this enigma of constraint in the face of an exceptional ability to change, we investigated an unprecedented reorganization of the standard lepidopteran chromosome structure in the green-veined white butterfly (Pieris napi). We find that gene content in P. napi has been extensively rearranged in large collinear blocks, which until now have been masked by a haploid chromosome number close to the lepidopteran average. We observe that ancient chromosome ends have been maintained and collinear blocks are enriched for functionally related genes suggesting both a mechanism and a possible role for selection in determining the boundaries of these genome-wide rearrangements.Peer reviewe

The jumping spider Saitis barbipes lacks a red photoreceptor to see its own sexually dimorphic red coloration

Examining the role of color in mate choice without testing what colors the study animal is capable of seeing can lead to ill-posed hypotheses and erroneous conclusions. Here, we test the seemingly reasonable assumption that the sexually dimorphic red coloration of the male jumping spider Saitis barbipes is distinguishable, by females, from adjacent black color patches. Using microspectrophotometry, we find clear evidence for photoreceptor classes with maximal sensitivity in the UV (359 nm) and green (526 nm), inconclusive evidence for a photoreceptor maximally sensitive in the blue (451 nm), and no evidence for a red photoreceptor. No colored filters within the lens or retina could be found to shift green sensitivity to red. To quantify and visualize whether females may nevertheless be capable of discriminating red from black color patches, we take multispectral images of males and calculate photoreceptor excitations and color contrasts between color patches. Red patches would be, at best, barely discriminable from black, and not discriminable from a low-luminance green. Some color patches that appear achromatic to human eyes, such as beige and white, strongly absorb UV wavelengths and would appear as brighter “spider-greens” to S. barbipes than the red color patches. Unexpectedly, we discover an iridescent UV patch that contrasts strongly with the UV-absorbing surfaces dominating the rest of the spider. We propose that red and black coloration may serve identical purposes in sexual signaling, functioning to generate strong achromatic contrast with the visual background. The potential functional significance of red coloration outside of sexual signaling is discussed

Chromatic and luminance wing-background and wing-wing contrasts

Contains chromatic and luminance wing-background and wing-wing contrasts

Data from: Sensory limitations and the maintenance of color polymorphisms: viewing the ‘alba’ female polymorphism through the visual system of male Colias butterflies

Although color polymorphisms are a widespread and conspicuous component of extant biodiversity, the selective pressures that act to maintain multiple morphs within populations remain poorly understood in most cases. In particular, the role that visual system limitations may play in maintaining multiple color morphs is not well explored. We used a female-limited color polymorphism common to the butterfly genus Colias, called the ‘alba’ polymorphism, to investigate the hypotheses that mate-searching males may struggle to discriminate pale ‘alba’ females from co-occurring heterospecific white butterflies and/or heterospecific ‘alba’ females, or that ‘alba’ females may be more difficult to detect than non-‘alba’ females in natural scenes. Such perceptual limitations may influence the relative mating rates of ‘alba’ versus non-‘alba’ females, contributing to the evolutionary persistence of both morphs. Based on receptor-noise-limited modeling of the male Colias visual system, we find that ‘alba’ females exhibit chromatic and luminance contrasts against background foliage that are most similar to the ‘alba’ females of other co-occurring Colias species and females of the co-occurring white butterfly Pieris rapae. When compared to other co-flying butterflies including non-‘alba’ females, ‘alba’ females are consistently lower in chromatic contrast against background, but higher in luminance contrast. When viewed side-by-side, we estimate that male Colias should be able to discriminate ‘alba’ females from other co-occurring heterospecific butterflies, including heterospecific ‘albas’. However, under field conditions that involve larger distances in space or time, males are likely to face challenges discriminating between conspecific ‘alba’ females and co-occurring heterospecific white butterflies, particularly heterospecific ‘alba’ females. Our results suggest that constraints arising from male visual function may be involved in the maintenance of this color polymorphism, particularly in populations that co-occur with other ‘alba’-polymorphic Colias species. We argue that such visual system constraints may play a larger role in the maintenance of color polymorphism than has been empirically appreciated to date

Raw Spectral Data Final

Contains reflectance data from the wings of Colias eurytheme, C. philodice, Pieris rapae, leaves of alfalfa (Medicago sativa), and irradiance data

Data from: Rapid divergence of wing volatile profiles between subspecies of the butterfly Pieris rapae (Lepidoptera: Pieridae)

Complex signaling traits such as pheromone profiles can play an important role in the early stages of reproductive isolation between populations. These signals can diverge along multiple trait axes, and signal receivers are often sensitive to subtle differences in signal properties. In the Lepidoptera, prior research has highlighted that natural selection can drive rapid chemical signal divergence, for instance via mate recognition to maintain species boundaries. Much less is known about the occurrence of such changes for predominantly sexually-selected chemical signals, such as those released by many male lepidopterans. We evaluated the divergence in male and female wing volatile profiles between two recently-isolated subspecies of the pierid butterfly Pieris rapae: Pieris rapae rapae and Pieris rapae crucivora. In laboratory settings, these subspecies exhibit strong pre-mating isolation, with females rejecting males of the opposite subspecies despite the fact that males direct equivalent courtship effort toward females of either subspecies. Using gas chromatography-mass spectrometry, we analyzed the volatile chemical profiles of individual males and females of each subspecies. We find that males of each subspecies differ in their wing volatile profiles, including quantitative differences in a male sex pheromone, ferrulactone. In contrast, female wing volatiles profiles have diverged significantly less. These sex-specific patterns suggest that male chemical profiles may play a role in the observed pre-mating isolation between these two subspecies, providing support for future investigations of sexually-selected chemical traits in population divergence

The interaction between the spermatophore and the bursa copulatrix as a model for coevolution and sexual conflict

The interaction between the spermatophore and the bursa copulatrix as a model for coevolution and sexual conflict. Annual retreat of the Computational and Systems Biolog

The interaction between the spermatophore and the bursa copulatrix as a model for coevolution and sexual conflict

The interaction between the spermatophore and the bursa copulatrix as a model for coevolution and sexual conflict. Annual Retreat of the Computational and Systems Biology Departmen