Additive Effects: Although specific genes involved in animal coloration have been identified, the underlying selection for genetic variation in color-specific adaptation is not well understood. Examining theAgoutigene and other loci in the deer mice of Nebraska, where predation selects for light-colored mice in light environments and dark-colored mice in dark environments,Linnenet al.(p.1312) find evidence of multiple genetic variants under selection affecting coloration. The light color of Sand Hills mice is not the result of a single large-effect mutation, but is because of many accumulated mutations, each with a smaller phenotypic effect.

Pigmentation has emerged as a premier model for understanding the genetic basis of phenotypic evolution, and a growing catalog of color loci is starting to reveal biases in the mutations, genes, and genetic architectures underlying color variation in the wild. However, existing studies have sampled a limited subset of taxa, color traits, and developmental stages. To expand the existing sample of color loci, we performed quantitative trait locus (QTL) mapping analyses on two types of larval pigmentation traits that vary among populations of the redheaded pine sawfly (Neodiprion lecontei): carotenoid-based yellow body color and melanin-based spotting pattern. For both traits, our QTL models explained a substantial proportion of phenotypic variation and suggested a genetic architecture that is neither monogenic nor highly polygenic. Additionally, we used our linkage map to anchor the current N. lecontei genome assembly. With these data, we identified promising candidate genes underlying: (1) a loss of yellow pigmentation in populations in the Mid-Atlantic/northeastern USA [C locus-associated membrane protein homologous to a mammalian HDL receptor-2 gene (Cameo2) and lipid transfer particle apolipoproteins II and I gene (apoLTP-II/I )], and (2) a pronounced reduction in black spotting in Great-Lakes populations [members of the yellow gene family, tyrosine hydroxylase gene (pale), and dopamine N-acetyltransferase gene (Dat)]. Several of these genes also contribute to color variation in other wild and domesticated taxa. Overall, our findings are consistent with the hypothesis that predictable genes of large-effect contribute to color evolution in nature.

Though seemingly bizarre, the dramatic morphological and ecological transformation that occurs when immature life stages metamorphose into reproductive adults is one of the most successful developmental strategies on the planet. The adaptive decoupling hypothesis (ADH) proposes that metamorphosis is an adaptation for breaking developmental links between traits expressed in different life stages, thereby facilitating their independent evolution when exposed to opposing selection pressures. Here, we draw inspiration from the ADH to develop a conceptual framework for understanding changes in gene expression across ontogeny. We hypothesized that patterns of stage‐biased and sex‐biased gene expression are the product of both decoupling mechanisms and selection history. To test this hypothesis, we characterized transcriptome‐wide patterns of gene‐expression traits for three ecologically distinct larval stages (all male) and adult males and females of a hypermetamorphic insect (Neodiprion lecontei). We found that stage‐biased gene expression was most pronounced between larval and adult males, which is consistent with the ADH. However, even in the absence of a metamorphic transition, considerable stage‐biased expression was observed among morphologically and behaviourally distinct larval stages. Stage‐biased expression was also observed across ecologically relevant Gene Ontology categories and genes, highlighting the role of ecology in shaping patterns of gene expression. We also found that the magnitude and prevalence of stage‐biased expression far exceeded adult sex‐biased expression. Overall, our results highlight how the ADH can shed light on transcriptome‐wide patterns of gene expression in organisms with complex life cycles. For maximal insight, detailed knowledge of organismal ecology is also essential.

Pine sawflies (Hymenoptera: Diprionidae) are eruptive herbivores found throughout eastern North America. The Diprionidae family, which contains at least 140 species, constitutes the most persistent threat to conifers as population outbreaks can cause widespread defoliation. Because some species are more prone to large, destructive outbreaks than others, species identification is critical to effective management. Although existing taxonomic keys are primarily based on internal adult morphology, substantial variation among species in larval color traits, geographic location, overwintering strategy, host plant, and egg patterns can be diagnostic at the species level. Here, we focus on the Pinaceae-feeding subfamily Diprioninae, of which there are 25 species in eastern North America. We describe the general biology, life cycle, and host-use ecology of Diprioninae, with an emphasis on the variation among these traits within this subfamily. In addition, we provide tools for species identification, including a taxonomic key that utilizes external diagnostic characteristics. Finally, we discuss available management strategies.