Scorpions possess two integrated multifunctional weapons systems. Anteriorly, they maintain a grasping system comprised of a pair of pedipalps ending in chelae that seize and manipulate prey, ward off predators, and secure mates. Posteriorly, they wield a venom delivery system consisting of a tail-like metasoma with a stinger at the tip of the terminal segment (telson) that can be thrust into prey, predators, or mates to inject venom. Given the complexity of these systems, I hypothesized that weaponry design is subject to selective forces arising from differences in usage between the sexes, during ontogeny, and among closely-related species occupying different habitats. In the first of three studies, I examined sexual dimorphism in the North American scorpion Hadrurus arizonesis to develop a suitable statistical approach for disentangling sexual size dimorphism (SSD) and sexual body component dimorphism (SBCD), and to characterize the allometry of weaponry components. In the second study, after thoroughly reviewing the literature on venom yield in scorpions, I relied on the methodology developed in the first study to characterize venom availability in H. arizonensis. Venom yield was strongly and exponentially related to overall body size and weakly proportional to relative telson size. Venom protein concentration was weakly and negatively associated with body size, and slightly greater in females than in males. In the third study, I examined both weapon systems of two sister Smeringurus species that co-occur with H. arizonensis but occupy distinct habitats: the psammophile S. mesaensis and the lithophile S. vachoni. Males trended toward more robust chela, especially in S. vachoni. Metasoma length averaged longer in males of both species, but the telson was larger and the venom supply greater in females. Venom availability increased exponentially during ontogeny for both species. Smeringurus vachoni possessed significantly larger venom stores than S. mesaensis. Sexual and species differences likely result from different selective regimes related to survival and reproductive demands, priority in securing mates, and possibly population density and cannibalism. These findings highlight the multiple factors that influence weapons design in scorpions, and underscore the functional importance of these complex systems that are relied upon in varying roles and contexts.
School of Medicine
Hayes, William K.
Brand, Leonard R.
Duerksen-Hughes, Penelope J.
Dunbar, Stephen G.
Doctor of Philosophy (PhD)
Year Degree Awarded
Date (Title Page)
Library of Congress/MESH Subject Headings
Scorpions; Sexual Dimorphism (Animals);
Subject - Local
Venom Availability; Weapon Systems; Ontogenetic Variation
Loma Linda University Libraries
This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.
Fox, Gerard A. A., "The Design of Complex Weapons Systems in Scorpions: Sexual, Ontogenetic, and Interspecific Variation" (2018). Loma Linda University Electronic Theses, Dissertations & Projects. 516.
Loma Linda University Electronic Theses and Dissertations
Loma Linda University. Del E. Webb Memorial Library. University Archives