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1. Wing serial homologues and the diversification of insect outgrowths: insights from the pupae of scarab beetles

   https://doi.org/10.1098/rspb.2020.2828  

   Hu, Yonggang; Moczek, Armin P. (January 2021, Proceedings of the Royal Society B: Biological Sciences)

   null (Ed.)

   Modification of serially homologous structures is a common avenue towards functional innovation in developmental evolution, yet ancestral affinities among serial homologues may be obscured as structure-specific modifications accumulate over time. We sought to assess the degree of homology to wings of three types of body wall projections commonly observed in scarab beetles: (i) the dorsomedial support structures found on the second and third thoracic segments of pupae, (ii) the abdominal support structures found bilaterally in most abdominal segments of pupae, and (iii) the prothoracic horns which depending on species and sex may be restricted to pupae or also found in adults. We functionally investigated 14 genes within, as well as two genes outside, the canonical wing gene regulatory network to compare and contrast their role in the formation of each of the three presumed wing serial homologues. We found 11 of 14 wing genes to be functionally required for the proper formation of lateral and dorsal support structures, respectively, and nine for the formation of prothoracic horns. At the same time, we document multiple instances of divergence in gene function across our focal structures. Collectively, our results support the hypothesis that dorsal and lateral support structures as well as prothoracic horns share a developmental origin with insect wings. Our findings suggest that the morphological and underlying gene regulatory diversification of wing serial homologues across species, life stages and segments has contributed significantly to the extraordinary diversity of arthropod appendages and outgrowths. 

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2. The Developmental Origin of Novel Complex Morphological Traits in Lepidoptera

   https://doi.org/10.1146/annurev-ento-021324-020504  

   Monteiro, Antónia; Murugesan, Suriya Narayanan; Prakash, Anupama; Papa, Riccardo (January 2025, Annual Review of Entomology)

   Novel traits in the order Lepidoptera include prolegs in the abdomen of larvae, scales, and eyespot and band color patterns in the wings of adults. We review recent work that investigates the developmental origin and diversification of these four traits from a gene-regulatory network (GRN) perspective. While prolegs and eyespots appear to derive from distinct ancestral GRNs co-opted to novel body regions, scales derive from in situ modifications of a sensory bristle GRN. The origin of the basal and central symmetry systems of bands on the wing is associated with the expression of theWntAgene in those regions, whereas the more marginal bands depend on two other genes,Distal-lessandspalt. Finally, several genes have been discovered that play important roles in regulating background wing color, via the regulation of pigmentation GRNs. The identification of shared and novelcis-regulatory elements of genes belonging to these distinct GRNs helps trace the developmental and evolutionary history of these traits. Future work should examine the extent to which ancestral GRNs are co-opted/modified to produce the novel traits and how these GRNs map to specific cell types in ancestral and derived traits. 

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3. Circulation In Insect Wings

   https://doi.org/10.1093/icb/icaa124  

   Salcedo, MK; Socha, JJ (September 2020, Integrative and comparative biology)

   Insect wings are living, flexible structures composed of tubular veins and thin wing membrane. Wing veins can contain hemolymph (insect blood), tracheae, and nerves. Continuous flow of hemolymph within insect wings ensures that sensory hairs, structural elements such as resilin, and other living tissue within the wings remains functional. While it is well known that hemolymph circulates through insect wings, the extent of wing circulation (e.g., whether flow is present in every vein, and whether it is confined to the veins alone) is not well understood, especially for wings with complex wing venation. Over the last 100 years, scientists have developed experimental methods including microscopy, fluorescence, and thermography to observe flow in the wings. Recognizing and evaluating the importance of hemolymph movement in insect wings is critical in evaluating how the wings function both as flight appendages, as active sensors, and as thermoregulatory organs. In this review, we discuss the history of circulation in wings, past and present experimental techniques for measuring hemolymph, and broad implications for the field of hemodynamics in insect wings. 

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4. Transient use of hemolymph for hydraulic wing expansion in cicadas

   https://doi.org/10.1038/s41598-023-32533-4  

   Salcedo, Mary K.; Ellis, Tyler E.; Sáenz, Ángela S.; Lu, Joyce; Worrell, Terrell; Madigan, Michael L.; Socha, John J. (December 2023, Scientific Reports)

   Abstract Insect wings must be flexible, light, and strong to allow dynamic behaviors such as flying, mating, and feeding. When winged insects eclose into adults, their wings unfold, actuated hydraulically by hemolymph. Flowing hemolymph in the wing is necessary for functioning and healthy wings, both as the wing forms and as an adult. Because this process recruits the circulatory system, we asked, how much hemolymph is pumped into wings, and what happens to the hemolymph afterwards? Using Brood X cicadas ( Magicicada septendecim ), we collected 200 cicada nymphs, observing wing transformation over 2 h. Using dissection, weighing, and imaging of wings at set time intervals, we found that within 40 min after emergence, wing pads morphed into adult wings and total wing mass increased to ~ 16% of body mass. Thus, a significant amount of hemolymph is diverted from body to wings to effectuate expansion. After full expansion, in the ~ 80 min after, the mass of the wings decreased precipitously. In fact, the final adult wing is lighter than the initial folded wing pad, a surprising result. These results demonstrate that cicadas not only pump hemolymph into the wings, they then pump it out, producing a strong yet lightweight wing. 

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5. Adaptive shifts underlie the divergence in wing morphology in bombycoid moths

   https://doi.org/10.1098/rspb.2021.0677  

   Aiello, Brett R.; Tan, Milton; Bin Sikandar, Usama; Alvey, Alexis J.; Bhinderwala, Burhanuddin; Kimball, Katalina C.; Barber, Jesse R.; Hamilton, Chris A.; Kawahara, Akito Y.; Sponberg, Simon (August 2021, Proceedings of the Royal Society B: Biological Sciences)

   null (Ed.)

   The evolution of flapping flight is linked to the prolific success of insects. Across Insecta, wing morphology diversified, strongly impacting aerodynamic performance. In the presence of ecological opportunity, discrete adaptive shifts and early bursts are two processes hypothesized to give rise to exceptional morphological diversification. Here, we use the sister-families Sphingidae and Saturniidae to answer how the evolution of aerodynamically important traits is linked to clade divergence and through what process(es) these traits evolve. Many agile Sphingidae evolved hover feeding behaviours, while adult Saturniidae lack functional mouth parts and rely on a fixed energy budget as adults. We find that Sphingidae underwent an adaptive shift in wing morphology coincident with life history and behaviour divergence, evolving small high aspect ratio wings advantageous for power reduction that can be moved at high frequencies, beneficial for flight control. By contrast, Saturniidae, which do not feed as adults, evolved large wings and morphology which surprisingly does not reduce aerodynamic power, but could contribute to their erratic flight behaviour, aiding in predator avoidance. We suggest that after the evolution of flapping flight, diversification of wing morphology can be potentiated by adaptative shifts, shaping the diversity of wing morphology across insects. 

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