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1. Melanic pigmentation and light preference within and between two Drosophila species

   Cooley, A.M. ; Schmitz, S. ; Cabrera, E. J. ; Cutter, M. ; Sheffield, M. ; Gingerich, I. ; Thomas, G. ; Lincoln, C. N. ; Moore, V. H. ; Moore, A. E. ; et al ( October 2021 , Ecology and evolution)

   null (Ed.)

   Environmental adaptation and species divergence often involve suites of co-evolving traits. Pigmentation in insects presents a variable, adaptive, and well-characterized class of phenotypes for which correlations with multiple other traits have been demonstrated. In Drosophila, the pigmentation genes ebony and tan have pleiotropic effects on flies’ response to light, creating the potential for correlated evolution of pigmentation and vision. Here we investigate differences in light preference within and between two sister species, Drosophila americana and D. novamexicana, which differ in pigmentation in part because of evolution at ebony and tan, and occupy environments that differ in many variables including solar radiation. We hypothesized that lighter pigmentation would be correlated with a greater preference for environmental light, and tested this hypothesis using a habitat choice experiment. In a first set of experiments, using males of D. novamexicana line N14 and D. americana line A00, the light-bodied D. novamexicana was found slightly but significantly more often than D. americana in the light habitat. A second experiment, which included additional lines and females as well as males, failed to find any significant difference between D. novamexicana-N14 and D. americana-A00. Additionally, the other dark line of D. americana (A04) was found in the light habitat more often than the light-bodied D. novamexicana-N14, in contrast to our predictions. However, the lightest line of D. americana, A01, was found substantially and significantly more often in the light habitat than the two darker lines of D. americana, thus providing partial support for our hypothesis. Finally, across all four lines, females were found more often in the light habitat than their more darkly-pigmented male counterparts. Additional replication is needed to corroborate these findings and evaluate conflicting results, with the consistent effect of sex within and between species providing an especially intriguing avenue for further research. 

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2. Genetic architecture of a body colour cline in Drosophila americana

   https://doi.org/10.1111/mec.15531  

   Sramkoski, Lisa L. ; McLaughlin, Wesley N. ; Cooley, Arielle M. ; Yuan, David C. ; John, Alisha ; Wittkopp, Patricia J. ( July 2020 , Molecular Ecology)

   Phenotypic variation within a species is often structured geographically in clines. InDrosophila americana, a longitudinal cline for body colour exists within North America that appears to be due to local adaptation. Thetanandebonygenes have been hypothesized to contribute to this cline, with alleles of both genes that lighten body colour found inD. americana. These alleles are similar in sequence and function to the allele fixed inD. americana'smore lightly pigmented sister species,Drosophila novamexicana. Here, we examine the frequency and geographic distribution of theseD. novamexicana‐like alleles inD. americana. Among alleles from over 100 strains ofD. americanaisolated from 21 geographic locations, we failed to identify additional alleles oftanorebonywith as much sequence similarity toD. novamexicanaas theD. novamexicana‐like alleles previously described. However, using genetic analysis of 51D. americanastrains derived from 20 geographic locations, we identified one new allele ofebonyand one new allele oftansegregating inD. americanathat are functionally equivalent to theD. novamexicanaallele. An additional 5 alleles oftanalso showed marginal evidence of functional similarity. Given the rarity of these alleles, however, we conclude that they are unlikely to be driving the pigmentation cline. Indeed, phenotypic distributions of the 51 backcross populations analysed indicate a more complex genetic architecture, with diversity in the number and effects of loci altering pigmentation observed both within and among populations ofD. americana. This genetic heterogeneity poses a challenge to association studies and genomic scans for clinal variation, but might be common in natural populations.

    

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3. Orange ornamentation increases sex-specific conspicuousness of juvenile males to conspecifics and predators

   https://doi.org/10.1093/biolinnean/blae035  

   Agan, Jaina ; Macedonia, Joseph M. ; Grindstaff, Jennifer L. ; Fox, Stanley F. ( April 2024 , Biological Journal of the Linnean Society)

   Many animal species have evolved striking colour patterns that attract the opposite sex and intimidate rivals. Although conspicuous coloration is usually restricted to adults in the context of reproduction, this is not always the case. Juvenile collared lizards (Crotaphytus collaris) are sexually dichromatic, wherein males exhibit ‘dorsolateral bars’ that are bright orange and showy, whereas females are light tan and inconspicuous. Given that adult male collared lizards suffer increased predation because of bright adult coloration, we hypothesized that juvenile males might also be more detectable to predators owing to the conspicuousness of their dorsolateral bars. To test this hypothesis, we measured the reflectance of the dorsolateral bars, non-bar background body regions, and the rocky habitat in which the lizards live. We modelled the vision of our study species and its dominant predators to quantify and compare statistically the contrasts of male and female dorsolateral bars against the natural rock background. We also calculated lizard survivorship over a 4 year study period. We found that male orange bars exhibited significantly higher chromatic contrast, but significantly lower achromatic contrast, than female bars when perceived through all visual models. However, the dorsolateral background colour of juvenile males and females did not differ significantly in chromatic or achromatic contrast from rocks in any visual model. Female lizards survived better than male lizards to the yearling (reproductive) stage. Our findings indicate that juvenile male bars are conspicuous both to conspecifics and to predators and that the bars probably increase predation on juvenile males.

    

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4. What about Females? Urban Female Song Sparrows Elevate Aggressive Signaling Compared to Rural

   https://doi.org/10.1093/icb/icac106  

   Lane, Samuel J. ; Sewall, Kendra B. ( July 2022 , Integrative And Comparative Biology)

   The costs and benefits of breeding behaviors are influenced by environmental conditions, and habitat variation can shift the degree to which behaviors are expressed. Novel urban habitats have been shown to differ significantly in disturbances such as noise, light at night, and human presence, as well as resource availability, compared to rural habitats. Perhaps because of these environmental differences, urban males of several species are consistently more aggressive than rural males, raising the hypothesis that greater territorial aggression is beneficial in urban habitats. Though often ignored, female songbirds of many species also perform aggressive territorial behaviors toward conspecifics during the breeding season. For socially monogamous songbirds, this aggression functions to ensure partner fidelity and secure resources for reproduction. Studies of the effects of urbanization on songbird behavior have yet to determine if urban females also express greater territorial aggression. Importantly, energetically demanding behaviors such as territoriality and parental care should constrain one another, leading to behavioral trade-offs during the breeding season. Though territorial aggression and parental care are inversely related in males of several species of songbird, this relationship is understudied in female songbirds, particularly those facing environmental change, such as urbanization. In this study, we compared aggressive signaling and a measure of parental care (maternal nest visitation rates) between female song sparrows (Melospiza melodia), living in urban and rural habitats. We hypothesized that female aggressive signaling would be higher in urban environments compared to rural, and negatively correlated with maternal visitation rates. We found that urban females, like males, expressed increased aggressive signaling compared to rural. However, female aggressive signaling was not related to our measure of maternal care, suggesting females aren't facing a trade-off between these two behaviors. Collectively, our results are consistent with the hypothesis that urban habitats promote territorial aggression in female song sparrows. As urbanization continues to spread, understanding the behavioral changes animals employ in urban environments requires studying individuals of different sexes and age classes, and will help us understand how some species are able to cope with human-induced rapid environmental change.

    

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5. Size doesn't matter, sex does: a test for boldness in sister species of Brachyrhaphis fishes

   https://doi.org/10.1002/ece3.1304  

   Ingley, Spencer J. ; Rehm, Jeremy ; Johnson, Jerald B. ( October 2014 , Ecology and Evolution)

   The effect of divergent natural selection on the evolution of behavioral traits has long been a focus of behavioral ecologists. Predation, due to its ubiquity in nature and strength as a selective agent, has been considered an important environmental driver of behavior. Predation is often confounded with other environmental factors that could also play a role in behavioral evolution. For example, environments that contain predators are often more ecologically complex and “risky” (i.e., exposed and dangerous). Previous work shows that individuals from risky environments are often more bold, active, and explorative than those from low‐risk environments. To date, most comparative studies of environmentally driven behavioral divergence are limited to comparisons among populations within species that occur in divergent selective environments but neglect comparisons between species following speciation. This limits our understanding of how behavior evolves post‐speciation. The Central American live‐bearing fish genusBrachyrhaphisprovides an ideal system for examining the relationship between selective environments and behavior, within and between species. Here, we test for differences in boldness between sister speciesB. roseniandB. terrabensisthat occur in streams with and without piscivorous predators, respectively. We found that species do differ in boldness, with species that occur with predators being bolder than those that do not. Within each species, we found that sexes differed in boldness, with males being bolder than females. We also tested for a relationship between size (a surrogate for metabolic rate) and boldness, but found no size effects. Therefore, sex, not size, affects boldness. These results are consistent with the hypothesis that complex and risky environments favor individuals with more bold behavioral traits, but they are not consistent with the hypothesis that size (and therefore metabolic rate) drives divergence in boldness. Finally, our results provide evidence that behavioral trait divergence continues even after speciation is complete.

    

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