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1. Evolutionary and Biomechanical Basis of Drumming Behavior in Woodpeckers

   https://doi.org/10.3389/fevo.2021.649146  

   Schuppe, Eric R.; Rutter, Amy R.; Roberts, Thomas J.; Fuxjager, Matthew J. (July 2021, Frontiers in Ecology and Evolution)

   null (Ed.)

   Understanding how and why behavioral traits diversify during the course of evolution is a longstanding goal of organismal biologists. Historically, this topic is examined from an ecological perspective, where behavioral evolution is thought to occur in response to selection pressures that arise through different social and environmental factors. Yet organismal physiology and biomechanics also play a role in this process by defining the types of behavioral traits that are more or less likely to arise. Our paper explores the interplay between ecological, physiological, and mechanical factors that shape the evolution of an elaborate display in woodpeckers called the drum. Individuals produce this behavior by rapidly hammering their bill on trees in their habitat, and it serves as an aggressive signal during territorial encounters. We describe how different components of the display—namely, speed (bill strikes/beats sec –1 ), length (total number of beats), and rhythm—differentially evolve likely in response to sexual selection by male-male competition, whereas other components of the display appear more evolutionarily static, possibly due to morphological or physiological constraints. We synthesize research related to principles of avian muscle physiology and ecology to guide inferences about the biomechanical basis of woodpecker drumming. Our aim is to introduce the woodpecker as an ideal study system to study the physiological basis of behavioral evolution and how it relates to selection born through different ecological factors. 

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2. Evaluating the light environment as a contributor to colour differences among related bird species

   https://doi.org/10.1093/biolinnean/blae117  

   Fialko, Kristina; Price, Trevor_D (February 2025, Biological Journal of the Linnean Society)

   Abstract Understanding the diversity of colour in nature has been one of the more elusive evolutionary problems. In the terrestrial environment, comparative analyses have associated differences in colour between species to light environment, background, and receiver perception. However, these account for only a small fraction of colour diversity, and it has been difficult to explain why a certain species is the colour it is. Here we examine colour variation across 12 very similar species of warblers belonging to the genus Phylloscopus, whose general brightness along an achromatic axis has previously been related to light intensity in their habitat. Many of these species also show variation in the colour of several plumage regions, including the wing bar, belly, and white vs. green in the outer tail feathers. We ask if these differences can be connected to the spectrum of light found in the habitat of each species. We find little evidence that contrast between patches and adjacent plumage or colour per se is affected by light environment. We argue that the heterogeneity of light environments experienced within a habitat and throughout the day make it unlikely that downwelling irradiance alone has a direct influence on colour variation. Accordingly, other features must have driven colour evolution. Diversification may be driven by environmental characteristics, such as background, or unrelated to environment altogether, reflecting the possibility that many different variants may effectively stimulate a receiver, and those that appear in a certain species reflect stochastic processes (e.g. mutation) and contingency (form of the ancestor). 

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3. A bird’s-eye view reveals no fixed differences in plumage coloration between divergent populations of Painted Buntings

   https://doi.org/10.1007/s10336-024-02232-6  

   Podkowa, Pawel; Hogan, Benedict_G; Stoddard, Mary_Caswell; Hill, Geoffrey_E (November 2024, Journal of Ornithology)

   Abstract In birds, the process of speciation is closely associated with transitions in ornamentation, including coloration, plumage pattern, and song. To investigate the origins of these shifts and their connection to genetic changes, we conducted a study on one of the most highly ornamented songbirds, the Painted Bunting (Passerina ciris). The male Painted Buntings exhibits a stunning array of colors, with a red chest, blue head, green back, green coverts, and pink rump. In addition, Painted Buntings show a high level of genetic structure, with eastern and western populations that have fixed genetic differences in both nuclear and mitochondrial genes. Using non-invasive spectrophotometry techniques, we measured the coloration of six plumage patches on 88 museum specimens of male Painted Buntings in definitive plumage from across the range of the species. We predicted that there would be divergence between the genetically distinct eastern and western populations in ornamental coloration that is perceptible to a bunting but imperceptible to a human observer. However, we measured no consistent nor substantial difference in the plumage coloration of males from different populations. The observation of substantial divergence in nuclear and mitochondrial genotype with no change in ornamental coloration between populations of a brightly colored bird has important implications for the role of sexual selection in the process of speciation. 

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4. A rapidly evolving cricket produces percussive vibrations: how, who, when, and why

   https://doi.org/10.1093/beheco/arad031  

   Wikle, Aaron W.; Broder, E. Dale; Gallagher, James H.; Tinghitella, Robin M.; Snell-Rood, ed., Emilie (May 2023, Behavioral Ecology)

   Abstract Sexual signals are often transmitted through multiple modalities (e.g., visual and chemical) and under selection from both intended and unintended receivers. Each component of a multimodal signal may be more or less conspicuous to receivers, and signals may evolve to take advantage of available private channels. We recently documented percussive substrate-borne vibrations in the Pacific field cricket (Teleogryllus oceanicus), a species that uses airborne acoustic and chemical signals to attract and secure mates. The airborne signals of Hawaiian T. oceanicus are currently undergoing rapid evolution; at least five novel male morphs have arisen in the past 20 years. Nothing is yet known about the newly discovered percussive substrate-borne vibrations, so we ask “how” they are produced, “who” produces them (e.g., population, morph), “when” they produce them (e.g., whether they are plastic), and “why” (e.g., do they play a role in mating). We show that the vibrations are produced exclusively by males during courtship via foreleg drumming. One novel morph, purring, produces quieter airborne songs and is more likely to drum than the ancestral morph. However, drumming behavior is also contextually plastic for some males; when we removed the ability of males to produce airborne song, ancestral males became more likely to drum, whereas two novel morphs were equally likely to drum regardless of their ability to produce song. Opposite our prediction, females were less likely to mate with males who drummed. We discuss why that might be and describe what we can learn about complex signal evolution from this newly discovered behavior. 

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5. Leaf‐footed bugs possess multiple hidden contrasting color signals, but only one is associated with increased body size

   https://doi.org/10.1002/ece3.6468  

   Emberts, Zachary; Miller, Christine W.; Skojec, Chelsea; Shepherd, Rachel; St. Mary, Colette M. (July 2020, Ecology and Evolution)

   Abstract Antipredatory displays that incorporate hidden contrasting coloration are found in a variety of different animals. These displays are seen in organisms that have drab coloration at rest, but when disturbed reveal conspicuous coloration. Examples include the bright abdomens of mountain katydids and the colorful underwings of hawk moths. Such hidden displays can function as secondary defenses, enabling evasion of a pursuant predator. To begin to understand why some species have these displays while others do not, we conducted phylogenetic comparative analyses to investigate factors associated with the evolution of hidden contrasting coloration in leaf‐footed bugs. First, we investigated whether hidden contrasting coloration was associated with body size because these displays are considered to be more effective in larger organisms. We then investigated whether hidden contrasting coloration was associated with an alternative antipredatory defense, in this case rapid autotomy. We found that leaf‐footed bugs with hidden contrasting coloration tended to autotomize more slowly, but this result was not statistically significant. We also found that the presence of a body size association was dependent upon the form of the hidden color display. Leaf‐footed bugs that reveal red/orange coloration were the same size, on average, as species without a hidden color display. However, species that reveal white patches on a black background were significantly larger than species without a hidden color display. These results highlight the diversity of forms that hidden contrasting color signal can take, upon which selection may act differently. 

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