Development time integrates temperature and host plant cues for eyespot size in three tropical satyrine butterflies

Many tropical butterflies have distinct wet and dry season adult morphs differing in the size of wing eyespots. Eyespot size is influenced by the environment experienced by developing larvae, and this plasticity is adaptive because the morphs have higher survival in their respective seasons. Higher temperature during the larval phase produces adults with larger eyespots in many species. This reaction norm is adaptive when high temperatures precede the wet season, which is not the case in all regions. Therefore, butterflies may rely on another environmental cue such as host plant species, and may also integrate information from multiple environmental variables through their combined effect on larval developmental time. To test this, we manipulated developmental time of sympatric populations of three butterflies - Ypthima huebneri, Mycalesis mineus and Melanitis leda - using combinations of temperatures and host plant species. Higher rearing temperature correlated with larger eyespot size in all species. Host plant species independently affected eyespot size. The effects of temperature and host plant differed between species, sexes, and between the forewing and hindwing, suggesting differential selection pressures on eyespots. Nevertheless, information about temperature and host plant species may be integrated through developmental time, because shorter larval development time was correlated with larger eyespots in adults. However, there were exceptions within specific treatments, species, and eyespots. Our results highlight the complex control of eyespot size, which is likely influenced by a network of interacting factors. Our study also demonstrates how sympatric populations of different species interpret similar environmental cues differently.

Strong bat predation and weak environmental constraints predict longer moth tails

Elaborate traits evolve via intense selective pressure, overpowering ecological constraints. Hindwing tails that thwart bat attack have repeatedly originated in moon moths (Saturniidae), with longer tails having greater anti-predator effect. Here, we take a macroevolutionary approach to evaluate the evolutionary balance between predation pressure and possible limiting environmental factors on tail elongation. To trace the evolution of tail length across time and space, we inferred a time-calibrated phylogeny of the entirely tailed moth group (Actias + Argema) and performed ancestral state reconstruction and biogeographical analyses. We generated metrics of predation via estimates of bat abundance from nearly 200 custom-built species distribution models and environmental metrics via estimates of bioclimatic variables associated with individual moth observations. To access community science data, we developed a novel method for measuring wing lengths from un-scaled photos. Integrating these data into phylogenetically informed mixed models, we find a positive association between bat predation pressure and moth tail length and body size, and a negative association between environmental factors and these morphological traits. Regions with more insectivorous bats and more consistent temperatures tend to host longer-tailed moths. Our study provides insight into tradeoffs between biotic selective pressures and abiotic constraints that shape elaborate traits across the tree of life.

Ontogenetic trajectories and early shape differentiation of treehopper pronota (Hemiptera: Membracidae)

Membracids (family: Membracidae), commonly known as treehoppers, are recognizable by their enlarged and often elaborated pronota. Much of the research investigating the development and evolution of this structure has focused on the fifth instar to adult transition, in which the pronotum undergoes the largest transformation as it takes on adult identity. However, little is known about the earlier nymphal stages, the degree to which the pronotum develops at these timepoints, and how development has changed relative to the ancestral state. Here, we studied the nymphal stages and adults of five morphologically distinct membracid species and of Aetalion reticulatum (family: Aetalionidae), the outgroup which was used as an ancestral state proxy. We found that shape differentiation in the pronotum of membracids can start as early as the second instar stage. Most shape differentiation occurs within the nymphal stages and not in the embryo since the shape of the first-instar pronotum did not differ from the outgroup species in all but one species we investigated. We found the anterior-posterior axis of the pronotum elongated at a faster relative rate in membracid species than in A. reticulatum, which contributed to the development of exaggerated pronotal size. Finally, we found differences in the morphogenesis of shape across species. We suggest this is due to the developmental and evolutionary divergence of differential growth patterning of the dorsal surface of the pronotum, not only across species, but also between stages within the same species. This lability may contribute to the evolvability and diversification of the membracid pronotum.

The roles of growth regulation and appendage patterning genes in the morphogenesis of treehopper pronota

Treehoppers of the insect family Membracidae have evolved enlarged and elaborate pronotal structures, which is hypothesized to involve co-opted expression of genes that are shared with the wings. Here, we investigate the similarity between the pronotum and wings in relation to growth. Our study reveals that the ontogenetic allometry of the pronotum is similar to that of wings in Membracidae, but not the outgroup. Using transcriptomics, we identify genes related to translation and protein synthesis, which are mutually upregulated. These genes are implicated in the eIF2, eIF4/p70S6K and mTOR pathways, and have known roles in regulating cell growth and proliferation. We find that species-specific differential growth patterning of the pronotum begins as early as the third instar, which suggests that expression of appendage patterning genes occurs long before the metamorphic molt. We propose that a network related to growth and size determination is the more likely mechanism shared with wings. However, regulators upstream of the shared genes in pronotum and wings need to be elucidated to substantiate whether co-option has occurred. Finally, we believe it will be helpful to distinguish the mechanisms leading to pronotal size from those regulating pronotal shape as we make sense of this spectacular evolutionary innovation.

Genetic assimilation and accommodation: Models and mechanisms

Genetic assimilation and genetic accommodation are mechanisms by which novel phenotypes are produced and become established in a population. Novel characters may be fixed and canalized so they are insensitive to environmental variation, or can be plastic and adaptively responsive to environmental variation. In this review we explore the various theories that have been proposed to explain the developmental origin and evolution of novel phenotypes and the mechanisms by which canalization and phenotypic plasticity evolve. These theories and models range from conceptual to mathematical and have taken different views of how genes and environment contribute to the development and evolution of the properties of phenotypes. We will argue that a deeper and more nuanced understanding of genetic accommodation requires a recognition that phenotypes are not static entities but are dynamic system properties with no fixed deterministic relationship between genotype and phenotype. We suggest a mechanistic systems-view of development that allows one to incorporate both genes and environment in a common model, and that enables both quantitative analysis and visualization of the evolution of canalization and phenotypic plasticity.

Vanadium and insulin: Partners in metabolic regulation

Since the 1970s, the biological role of vanadium compounds has been discussed as insulin-mimetic or insulin-enhancer agents. The action of vanadium compounds has been investigated to determine how they influence the insulin signaling pathway. Khan and coworkers proposed key proteins for the insulin pathway study, introducing the concept "critical nodes". In this review, we also considered critical kinases and phosphatases that participate in this pathway, which will permit a better comprehension of a critical node, where vanadium can act: a) insulin receptor, insulin receptor substrates, and protein tyrosine phosphatases; b) phosphatidylinositol 3'-kinase, 3-phosphoinositide-dependent protein kinase and mammalian target of rapamycin complex, protein kinase B, and phosphatase and tensin homolog; and c) insulin receptor substrates and mitogen-activated protein kinases, each node having specific negative modulators. Additionally, leptin signaling was considered because together with insulin, it modulates glucose and lipid homeostasis. Even in recent literature, the possibility of vanadium acting against metabolic diseases or cancer is confirmed although the mechanisms of action are not well understood because these critical nodes have not been systematically investigated. Through this review, we establish that vanadium compounds mainly act as phosphatase inhibitors and hypothesize on their capacity to affect kinases, which are critical to other hormones that also act on common parts of the insulin pathway.

Allometry, Scaling, and Ontogeny of Form-An Introduction to the Symposium

Until recently, the study of allometry has been mostly descriptive, and consisted of a diversity of methods for fitting regressions to bivariate or multivariate morphometric data. During the past decade, researchers have been developing methods to extract biological information from allometric data that could be used to deduce the underlying mechanisms that gave rise to the allometry. In addition, an increasing effort has gone into understanding the kinetics of growth and the regulatory mechanisms that control growth of the body and its component parts. The study of allometry and scaling has now become an exceptionally diverse field, with different investigators applying state of the art methods and concepts in evolution, developmental biology, cell biology, and genetics. Diversity has caused divergence, and we felt that although there is general agreement about the new goals for the study of allometry (understanding underlying mechanisms and how those evolve to produce different morphologies), progress is hindered by lack of coordination among the different approaches. We felt the time was right to bring these diverse practitioners together in a symposium to discuss their most recent work in the hope of forging new functional, conceptual, and collaborative connections among established and novice practitioners.

Why the Static Allometry of Sexually-Selected Traits Is So Variable: The Importance of Function

Sexually-selected traits often show positive static allometry, with large individuals bearing disproportionately large structures. But many other sexually-selected traits show isometry or even negative allometry, with trait size varying relatively little with body size. We recently proposed that the functions of these traits (as aggressive signals, weapons, courtship signals, and contact courtship devices) determine their allometries. Positive allometry is generally favored for aggressive signals because aggressive signals are selected to emphasize body size (and thus fighting prowess). In contrast, the biomechanics of force application in weapons only sometimes select for positive allometry; the content of courtship signals is even less often related to body size; and contact courtship devices are selected to be relatively invariant across body sizes. Here we summarize the arguments in favor of this “functional allometry” hypothesis and expand a comparative test of its predictions. Our results indicate that sexual traits have the allometric slopes predicted by our hypothesis, regardless of which body part bears the structure.