title: Biomechanics of ant (Hymenoptera: Formicidae) bite Effects of mandible and head morphology
Creators: name: Klunk, Cristian Luan
Publisher: name: UNSPECIFIED
Year: 2023

description: The necessity to capture and process food represents a relevant evolutionary pressure. Insects are incredibly diverse, showing several feeding modes and their associated morphological adaptations. Many insect lineages evolved a chewing feeding mode, where the mandibles are essential appendices to cut, crush, and tear food items that are further processed by other mouthparts. Mandibles can also be employed to perform additional behaviors. In ants, workers use their mandibles to execute most of the colony's non-reproductive tasks, like carry brood and objects, excavate, cut, crush, and punch. Not surprisingly, this heavy reliance on mandibles leads to a significant development of the mandibular muscles in ant workers, especially the mandibular closing muscles, the largest of an ant worker. Those muscles originate in the head capsule, whose shape has relevant consequences for muscle packing. Ants show an astounding head and mandible morphological diversity, whose functional implications have been investigated through distinct approaches, but usually regarding closely related species. Some ant species have further morphological variation among the workers, characterizing a worker polymorphism with profound implications for the colony division of labor. Biomechanical simulations can be effectively used to test a structure's functional performance under external loading. Concerning ant worker heads and mandibles, the functional relevance of the morphological variation observed in different lineages, or even among distinct worker types of the same species, could be investigated through simulations that resemble bite-loading conditions. Finite Element Analysis (FEA) is a numerical method used to approximate the mechanical responses of a structure to an external load. With digital reconstructions of the target structure, it is possible to perform an FEA, providing the relevant mechanical aspects of the behavior intended to simulate, like an ant bite. The main aim of this thesis is to explore the morphological variation observed in ant worker heads and mandibles under a functional perspective at two levels: intra and interspecifically. We employed FEA to test the mechanical responses of ant worker heads and mandibles under bite loading conditions, comparing the functional performance of major and minor workers of the dimorphic ant genus Pheidole at the intraspecific level, and of several ant lineages that span many of the currently recognized ant subfamilies at the interspecific level. Our results suggest that in the genus Pheidole, the major worker subcaste have heads and mandibles better suited to deal with the mechanical demands of bite, agreeing with its duties in the colony as workers responsible for defense and food processing. At the interspecific level, head and mandible morphology variation were also relevant in the mechanical responses of those structures to bite-loading demands, although with unclear relationships with ecological aspects. We demonstrated that FEA is a valuable tool to explore functional aspects of ant morphological variation and to provide insights into ant morphological evolution.