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Title:Comparative biomechanics and functional morphology of latch-mediated spring actuated mandibles in ants
Author(s):Gibson, Joshua C
Director of Research:Suarez, Andrew V.
Doctoral Committee Chair(s):Suarez, Andrew V.
Doctoral Committee Member(s):Alleyne, Marianne; Whitfield, James B.; Anderson, Philip S. L.
Department / Program:Entomology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):trap-jaw ant
functional morphology
Abstract:Speed is a fundamental trait in many animals; the ability to move quickly to capture prey or evade predators is vital to the success of many species. How quickly an animal can move is limited by a fundamental physiological tradeoff between how fast muscle fibers contract and how forceful those contractions are. To overcome this limitation many animals have evolved latch-mediated spring actuation (LaMSA) mechanisms that utilize elastic energy storage during a loading phase where movement is restricted by a latch element, followed by a rapid release once this latching element is disengaged. LaMSA powered movements are some of the fastest known in nature and often achieve accelerations that exceed those of engineered robotic mechanisms at similar scales. One of the most diverse group of animals to utilize LaMSA mechanisms are the trap-jaw ants, a polyphyletic group of ants (Hymenoptera: Formicidae) which use spring powered mandibles to rapidly capture or incapacitate prey. Trap-jaws have evolved independently more than four times across at least three subfamilies of ants, making them a good system to study both the evolutionary origins of morphologically and mechanically complex biological systems as well as the comparative biomechanics of LaMSA mechanisms. However, there is a lack of information on functional morphology and mandible kinematics for many of these trap-jaw ant groups and species, particularly in the subfamily Myrmicinae which contains the majority of trap-jaw ant species. My dissertation consists of four chapters and investigates the mechanics and functional morphology of trap-jaw mechanisms in ants, with an overarching goal of filling in gaps in knowledge about strike kinematics of trap-jaw ant lineages. In Chapter 1, I introduce the trap-jaw ant system and describe what is currently known about trap-jaw mechanisms in the tribe Odontomachini and trap-jaw ants in the subfamily Myrmicinae. I also outline areas of interest for future research on the biology of trap-jaw ants as well as set up the following chapters. In Chapter 2 I describe the mandible strike kinematics of four trap-jaw ant species in the genus Anochetus, focusing on two species, Anochetus emarginatus and Anochetus horridus, which have unusual morphologies for this genus of trap-jaw ants that more closely resemble those of their sister genus of trap-jaw ants, Odontomachus. I test whether performance in these species more closely resembles that found in Odontomachus or the more closely related Anochetus species. I find that two species, Anochetus targionii and Anochetus paripungens, have mandible strikes that overall closely resemble those found in Odontomachus, reaching a mean maximum rotational velocity and acceleration of around 3.7x104 rad/s and 8.5x108 rad/s2, respectively. In contrast, Anochetus horridus and Anochetus emarginatus have slower strikes relative to the other species of Anochetus and Odontomachus, reaching mean maximum rotational velocity and acceleration of around 1.3x104 rad/s and, 2x108 rad/s2, respectively. This variation in strike performance among species of Anochetus likely reflects differences in evolutionary history, physiology, and natural history among species. In Chapter 3 I examine the mandible strike kinematics of two polymorphic species of myrmicine trap-jaw ants: Daceton armigerum which is continuously polymorphic, and Orectognathus versicolor which has distinct minor and major castes. I test whether scaling of various aspects of strike performance with body size in these species matches scaling relationships seen across species of trap-jaw ants in the tribe Odontomachini, which collectively span a comparable range of body sizes. I find that strike performance in D. armigerum scales comparably with body size to the across species scaling observed in Odontomachini, whereas in O. versicolor a relationship between body size and strike performance was not observed for most strike performance metrics. These findings suggest that ontogenetic scaling relationships within a species do not necessarily mimic scaling relationships observed across phylogeny. In Chapter 4 I describe the functional morphology and strike kinematics of 11 species of Strumigenys trap-jaw ants and representative species from the Daceton clade of trap-jaw ants which have both independently evolved LaMSA mandibles. I find that strike performance in these species is on par with that of other trap-jaw ant groups, with Orectognathus antennatus having the record for the fastest mandible strike of any trap-jaw ant. Two genera in the Daceton clade closed their mandibles asynchronously despite possessing a latching mechanism that is morphologically analogous to trap-jaw ants in the genera Strumigenys and Daceton which produce synchronous mandible closure. I also show that species in the genera Colobostruma and Mesostruma possess a mandible latching mechanism, suggesting that they possess LaMSA mandibles despite lacking common modifications present in other genera in this group.
Issue Date:2021-07-14
Rights Information:Copyright 2021 Joshua Gibson
Date Available in IDEALS:2022-01-12
Date Deposited:2021-08

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