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Synopsis Biological armors have evolved across taxa as structural adaptations that provide protection from external forces while balancing mobility, metabolic cost, and functional trade-offs. These systems, from arthropod exoskeletons to vertebrate osteoderms, illustrate how natural selection shapes materials and morphology to optimize defense without compromising essential movement and physiological processes. The evolution of armor is constrained by biomechanical limits, as seen in the structural rigidity of heavily plated organisms and the flexible composites that integrate protective and dynamic properties. Methods used to study these systems—CT scanning, histology, finite element analysis, and mechanical testing—directly influence how the biological principles of armor are defined and understood. These approaches reveal the material properties and functional constraints of armored structures that can be translated into engineered applications through bioinspiration. Bioinspired designs informed by natural armor have led to innovations in impact-resistant materials, flexible ceramics, and modular protective systems. By integrating biomechanics, materials science, and evolutionary biology, this manuscript examines how armor evolves, functions, and informs bioinspired design.
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It Pays to Be Bumpy: Drag Reducing Armor in the Pacific Spiny Lumpsucker, Eumicrotremus orbis
Synopsis Armor is a multipurpose set of structures that has evolved independently at least 30 times in fishes. In addition to providing protection, armor can manipulate flow, increase camouflage, and be sexually dimorphic. There are potential tradeoffs in armor function: increased impact resistance may come at the cost of maneuvering ability; and ornate armor may offer visual or protective advantages, but could incur excess drag. Pacific spiny lumpsuckers (Eumicrotremus orbis) are covered in rows of odontic, cone-shaped armor whorls, protecting the fish from wave driven impacts and the threat of predation. We are interested in measuring the effects of lumpsucker armor on the hydrodynamic forces on the fish. Bigger lumpsuckers have larger and more complex armor, which may incur a greater hydrodynamic cost. In addition to their protective armor, lumpsuckers have evolved a ventral adhesive disc, allowing them to remain stationary in their environment. We hypothesize a tradeoff between the armor and adhesion: little fish prioritize suction, while big fish prioritize protection. Using micro-CT, we compared armor volume to disc area over lumpsucker development and built 3D models to measure changes in drag over ontogeny. We found that drag and drag coefficients decrease with greater armor coverage and vary consistently with orientation. Adhesive disc area is isometric but safety factor increases with size, allowing larger fish to remain attached in higher flows than smaller fish.
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- PAR ID:
- 10468281
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Integrative And Comparative Biology
- Volume:
- 63
- Issue:
- 3
- ISSN:
- 1540-7063
- Page Range / eLocation ID:
- 796 to 807
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1093/icb/icad076
