Yellow and the Novel Aposematic Signal, Red, Protect Delias Butterflies from Predators

To and fro in the archipelago: Repeated inter-island dispersal and New Guinea's orogeny affect diversification of Delias, the world's largest butterfly genus

The world's largest butterfly genus Delias, commonly known as Jezebels, comprises ca. 251 species found throughout Asia, Australia, and Melanesia. Most species are endemic to islands in the Indo-Australian Archipelago or to New Guinea and nearby islands in Melanesia, and many species are restricted to montane habitats over 1200 m. We inferred an extensively sampled and well-supported molecular phylogeny of the group to better understand the spatial and temporal dimensions of its diversification. The remarkable diversity of Delias evolved in just ca. 15-16 Myr (crown age). The most recent common ancestor of a clade with most of the species dispersed out of New Guinea ca. 14 Mya, but at least six subsequently diverging lineages dispersed back to the island. Diversification was associated with frequent dispersal of lineages among the islands of the Indo-Australian Archipelago, and the divergence of sister taxa on a single landmass was rare and occurred only on the largest islands, most notably on New Guinea. We conclude that frequent inter-island dispersal during the Neogene-likely facilitated by frequent sea level change-sparked much diversification during that period. Many extant New Guinea lineages started diversifying 5 Mya, suggesting that orogeny facilitated their diversification. Our results largely agree with the most recently proposed species group classification system, and we use our large taxon sample to extend this system to all described species. Finally, we summarize recent insights to speculate how wing pattern evolution, mimicry, and sexual selection might also contribute to these butterflies' rapid speciation and diversification.

Knockdowns of red Malphigian tubules reveal pigmentation roles in the milkweed bug

Classical Drosophila eye color mutations have unearthed a toolkit of genes that have permitted candidate gene studies of the outstanding diversity of coloration patterns in other insects. The gene underlying the eye color phenotypes of the red Malphigian tubules (red) fly mutant was mapped to a LysM domain gene of unknown molecular function. Here, we used RNAi to test the role of a red ortholog in the pigmentation of the milkweed bug Oncopeltus fasciatus, and contrast its effect with the ommochrome biosynthetic pathway gene vermilion (ver). Pigmentation was reduced in the cuticle of embryonic legs and first instar abdomens following parental RNAi against red, but not against ver, likely reflecting an effect on pterin biogenesis. Nymphal RNAi of red and ver both resulted in adult eye depigmentation, consistent with an effect on ommochrome content. These results suggest red loss-of-function impacts biochemically distinct types of pigments, and we discuss its putative role in the biogenesis of lysosome-related organelles such as ommochromasomes and pterinosomes.

Sexual selection on jumping spider color pattern: investigation with a new quantitative approach

How animals assess information encoded in individual color patches have been extensively studied, yet the role of both individual color patches and gross color pattern (i.e., the combination of color patches) remains understudied. We tested the functioning of both individual color patches and gross color pattern in sexual selection using the jumping spider Siler semiglaucus as a study system. We first quantified sexual dimorphism in S. semiglaucus in both individual patches and gross color pattern using the newly developed quantitative color pattern analysis (QCPA) framework. After detecting sexual differences in color coverage and pattern contrast, we manipulated the abdomen color pattern of males and had them engage in both female mate choice and male contest trials. Females spent more time watching males with lower pattern contrast and greater red coverage during mate assessment, suggesting that they evaluate information from both individual patches and gross color pattern of males. However, male color pattern had no significant effect on the outcomes of male contests. Thus, we suggest that the observed sexual color pattern dimorphism evolved primarily through female mate choice in S. semiglaucus. This is the first study to use QCPA framework to quantify sexual dimorphism in within-pattern conspicuousness from an intraspecific perspective in invertebrates. Our study also highlights the importance of both individual color patches and gross color pattern in sexual selection.

What's in a band? The function of the color and banding pattern of the Banded Swallowtail

Butterflies have evolved a diversity of color patterns, but the ecological functions for most of these patterns are still poorly understood. The Banded Swallowtail butterfly, Papilio demolion demolion, is a mostly black butterfly with a greenish-blue band that traverses the wings. The function of this wing pattern remains unknown. Here, we examined the morphology of black and green-blue colored scales, and how the color and banding pattern affects predation risk in the wild. The protective benefits of the transversal band and of its green-blue color were tested via the use of paper model replicas of the Banded Swallowtail with variations in band shape and band color in a full factorial design. A variant model where the continuous transversal green-blue band was shifted and made discontinuous tested the protective benefit of the transversal band, while grayscale variants of the wildtype and distorted band models assessed the protective benefit of the green-blue color. Paper models of the variants and the wildtype were placed simultaneously in the field with live baits. Wildtype models were the least preyed upon compared with all other variants, while gray models with distorted bands suffered the greatest predation. The color and the continuous band of the Banded Swallowtail hence confer antipredator qualities. We propose that the shape of the band hinders detection of the butterfly's true shape through coincident disruptive coloration; while the green color of the band prevents detection of the butterfly from its background via differential blending. Differential blending is aided by the green-blue color being due to pigments rather than via structural coloration. Both green and black scales have identical structures, and the scales follow the Bauplan of pigmented scales documented in other Papilio butterflies.

Experimental field tests of Batesian mimicry in the swallowtail butterfly Papilio polytes

The swallowtail butterfly Papilio polytes is known for its striking resemblance in wing pattern to the toxic butterfly Pachliopta aristolochiae and is a focal system for the study of mimicry evolution. Papilio polytes females are polymorphic in wing pattern, with mimetic and nonmimetic forms, while males are monomorphic and nonmimetic. Past work invokes selection for mimicry as the driving force behind wing pattern evolution in P. polytes. However, the mimetic relationship between P. polytes and P. aristolochiae is not well understood. In order to test the mimicry hypothesis, we constructed paper replicas of mimetic and nonmimetic P. polytes and P. aristolochiae, placed them in their natural habitat, and measured bird predation on replicas. In initial trials with stationary replicas and plasticine bodies, overall predation was low and we found no differences in predation between replica types. In later trials with replicas mounted on springs and with live mealworms standing in for the butterfly's body, we found less predation on mimetic P. polytes replicas compared to nonmimetic P. polytes replicas, consistent with the predator avoidance benefits of mimicry. While our results are mixed, they generally lend support to the mimicry hypothesis as well as the idea that behavioral differences between the sexes contributed to the evolution of sexually dimorphic mimicry.

Bioinspired Infrared Sensing Materials and Systems

Bioinspired engineering offers a promising alternative approach in accelerating the development of many man-made systems. Next-generation infrared (IR) sensing systems can also benefit from such nature-inspired approach. The inherent compact and uncooled operation of biological IR sensing systems provides ample inspiration for the engineering of portable and high-performance artificial IR sensing systems. This review overviews the current understanding of the biological IR sensing systems, most of which are thermal-based IR sensors that rely on either bolometer-like or photomechanic sensing mechanism. The existing efforts inspired by the biological IR sensing systems and possible future bioinspired approaches in the development of new IR sensing systems are also discussed in the review. Besides these biological IR sensing systems, other biological systems that do not have IR sensing capabilities but can help advance the development of engineered IR sensing systems are also discussed, and the related engineering efforts are overviewed as well. Further efforts in understanding the biological IR sensing systems, the learning from the integration of multifunction in biological systems, and the reduction of barriers to maximize the multidiscipline collaborations are needed to move this research field forward.

Biased generalization of salient traits drives the evolution of warning signals

The importance of receiver biases in shaping the evolution of many signalling systems is widely acknowledged. Here, we show that receiver bias can explain which traits evolve to become warning signals. For warning coloration, a generalization bias for a signalling trait can result from predators learning to discriminate unprofitable from profitable prey. However, because the colour patterns of prey are complex traits with multiple components, it is crucial to understand which of the many aspects of prey appearance evolve into signals. We provide experimental evidence that the more salient differences in prey traits give rise to greater generalization bias, corresponding to stronger selection towards trait exaggeration. Our results are based on experiments with domestic chickens as predators in a Skinner-box-like setting, and imply that the difference in appearance between profitable and unprofitable prey that is most rapidly learnt produces the greatest generalization bias. As a consequence, certain salient traits of unprofitable prey are selected towards exaggeration to even higher salience, driving the evolution of warning coloration. This general idea may also help to explain the evolution of many other striking signalling traits found in nature.