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1. Sensory adaptations reshaped intrinsic factors underlying morphological diversification in bats

   https://doi.org/10.1186/s12915-021-01022-3  

   Arbour, J. H. ; Curtis, A. A. ; Santana, S. E. ( April 2021 , BMC Biology)

   Morphological evolution may be impacted by both intrinsic (developmental, constructional, physiological) and extrinsic (ecological opportunity and release) factors, but can intrinsic factors be altered by adaptive evolution and, if so, do they constrain or facilitate the subsequent diversification of biological form? Bats underwent deep adaptive divergences in skull shape as they evolved different sensory modes; here we investigate the potential impact of this process on two intrinsic factors that underlie morphological variation across organisms, allometry, and modularity.

   We use comparative phylogenetic and morphometric approaches to examine patterns of evolutionary allometry and modularity across a 3D geometric morphometric dataset spanning all major bat clades. We show that allometric relationships diverge between echolocators and visually oriented non-echolocators and that the evolution of nasal echolocation reshaped the modularity of the bat cranium.

   Shifts in allometry and modularity may have significant consequences on the diversification of anatomical structures, as observed in the bat skull.

    

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2. Evolution of multivariate wing allometry in schizophoran flies (Diptera: Schizophora)

   https://doi.org/10.1111/jeb.13613  

   Rohner, Patrick T. ( March 2020 , Journal of Evolutionary Biology)

   The proximate and ultimate mechanisms underlying scaling relationships as well as their evolutionary consequences remain an enigmatic issue in evolutionary biology. Here, I investigate the evolution of wing allometries in the Schizophora, a group of higher Diptera that radiated about 65 million years ago, by studying static allometries in five species using multivariate approaches. Despite the vast ecological diversity observed in contemporary members of the Schizophora and independent evolutionary histories throughout most of the Cenozoic, size‐related changes represent a major contributor to overall variation in wing shape, both within and among species. Static allometries differ between species and sexes, yet multivariate allometries are correlated across species, suggesting a shared developmental programme underlying size‐dependent phenotypic plasticity. Static allometries within species also correlate with evolutionary divergence across 33 different families (belonging to 11 of 13 superfamilies) of the Schizophora. This again points towards a general developmental, genetic or evolutionary mechanism that canalizes or maintains the covariation between shape and size in spite of rapid ecological and morphological diversification during the Cenozoic. I discuss the putative roles of developmental constraints and natural selection in the evolution of wing allometry in the Schizophora.

    

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3. POPOVICH , encoding a C2H2 zinc-finger transcription factor, plays a central role in the development of a key innovation, floral nectar spurs, in Aquilegia

   https://doi.org/10.1073/pnas.2006912117  

   Ballerini, Evangeline S. ; Min, Ya ; Edwards, Molly B. ; Kramer, Elena M. ; Hodges, Scott A. ( August 2020 , Proceedings of the National Academy of Sciences)

   The evolution of novel features, such as eyes or wings, that allow organisms to exploit their environment in new ways can lead to increased diversification rates. Therefore, understanding the genetic and developmental mechanisms involved in the origin of these key innovations has long been of interest to evolutionary biologists. In flowering plants, floral nectar spurs are a prime example of a key innovation, with the independent evolution of spurs associated with increased diversification rates in multiple angiosperm lineages due to their ability to promote reproductive isolation via pollinator specialization. As none of the traditional plant model taxa have nectar spurs, little is known about the genetic and developmental basis of this trait. Nectar spurs are a defining feature of the columbine genusAquilegia(Ranunculaceae), a lineage that has experienced a relatively recent and rapid radiation. We use a combination of genetic mapping, gene expression analyses, and functional assays to identify a gene crucial for nectar spur development,POPOVICH(POP), which encodes a C2H2 zinc-finger transcription factor.POPplays a central role in regulating cell proliferation in theAquilegiapetal during the early phase (phase I) of spur development and also appears to be necessary for the subsequent development of nectaries. The identification ofPOPopens up numerous avenues for continued scientific exploration, including further elucidating of the genetic pathway of which it is a part, determining its role in the initial evolution of theAquilegianectar spur, and examining its potential role in the subsequent evolution of diverse spur morphologies across the genus.

    

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4. Serotonin signaling suppresses the nutrition‐responsive induction of an alternate male morph in horn polyphenic beetles

   https://doi.org/10.1002/jez.2413  

   Schwab, Daniel B. ; Newsom, Keeley D. ; Moczek, Armin P. ( September 2020 , Journal of Experimental Zoology Part A: Ecological and Integrative Physiology)

   Environment‐responsive development contributes significantly to the phenotypic variation visible to selection and as such possesses the potential to shape evolutionary trajectories. However, evaluation of the contributions of developmental plasticity to evolutionary diversification necessitates an understanding of the developmental mechanisms underpinning plastic trait expression. We investigated the role of serotonin signaling in the regulation and evolution of horn polyphenism in the beetle genusOnthophagus. Specifically, we assessed the role of serotonin indevelopmentby determining whether manipulating serotonin biosynthesis during the larval stage alters body size, developmental rate, and the formation of relative adult trait size in traits characterized by minimal (genitalia), moderate (elytra), and pronounced (horns) nutrition‐responsive development inO. taurus. Second, we assessed serotonin's role inevolutionby replicating a subset of our approaches across four species reflecting ancestral as well as derived conditions. Lastly, we employed immunohistochemical approaches to begin assessing whether serotonin may be acting via the endocrine or nervous system. Our results show that pharmacological manipulation of serotonin signaling affects overall size, developmental rate, and the body size threshold separating alternate male morphs. Threshold body sizes were affected across species, regardless of the severity of horn polyphenism, and independent of the precise morphological location of horns. However, histological assessments suggest it is unlikely serotonin functions as a neurotransmitter and instead may rely on other mechanisms that remain to be identified. We discuss the most important implications of our results for our understanding of the evolution of and through plasticity in horned beetles and beyond.

    

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5. Trait Loss in Evolution: What Cavefish Have Taught Us about Mechanisms Underlying Eye Regression

   https://doi.org/10.1093/icb/icad032  

   Sifuentes-Romero, Itzel ; Aviles, Ari M. ; Carter, Joseph L. ; Chan-Pong, Allen ; Clarke, Anik ; Crotty, Patrick ; Engstrom, David ; Meka, Pranav ; Perez, Alexandra ; Perez, Riley ; et al ( May 2023 , Integrative And Comparative Biology)

   Reduction or complete loss of traits is a common occurrence throughout evolutionary history. In spite of this, numerous questions remain about why and how trait loss has occurred. Cave animals are an excellent system in which these questions can be answered, as multiple traits, including eyes and pigmentation, have been repeatedly reduced or lost across populations of cave species. This review focuses on how the blind Mexican cavefish, Astyanax mexicanus, has been used as a model system for examining the developmental, genetic, and evolutionary mechanisms that underlie eye regression in cave animals. We focus on multiple aspects of how eye regression evolved in A. mexicanus, including the developmental and genetic pathways that contribute to eye regression, the effects of the evolution of eye regression on other traits that have also evolved in A. mexicanus, and the evolutionary forces contributing to eye regression. We also discuss what is known about the repeated evolution of eye regression, both across populations of A. mexicanus cavefish and across cave animals more generally. Finally, we offer perspectives on how cavefish can be used in the future to further elucidate mechanisms underlying trait loss using tools and resources that have recently become available.

    

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