Stabbing Spines: A review of the Biomechanics and Evolution of Defensive Spines

Abstract

Spines are ubiquitous in both plants and animals, and while most spines were likely originally used for defense, over time many have been modified in a variety of ways. Here we take an integrative approach to review the form, function, and evolution of spines as a defensive strategy in order to make new connections between physical mechanisms and functional behavior. While this review focuses on spines in mammals, we reference and draw ideas from the literature on spines in other taxa, including plants. We begin by exploring the biomechanics of defensive spines, their varied functions, and non-defensive modifications. We pay particular attention to the mechanics involved in passive puncture and the ways organisms have overcome limitations associated with the low energy input. We then focus on the ecological, physiological, and behavioral factors that promote the evolution of spiny defenses, including predator- and habitat-mediated hypotheses. While there is considerable evidence to support both, studies have generally found that (1) defensive spines are usually effective against one class of attacker (e.g., larger predators) but ineffective against others or even facilitate predation by others, and (2) species that are more visible or exposed to predators are under much stronger selection to evolve defensive spines or some other robust defense. What type of defensive morphology that evolves, however, is less predictable and probably strongly dependent on both the dominant source of predation and the habitat structure of the organism (e.g., arboreal, terrestrial, fossorial). We then explore traits that are often correlated with defensive spines and armor, potentially forming armor syndromes, suites of traits that evolve together with body armor in a correlated fashion. In mammals, these include aposematic warning coloration, locomotion style, diet, metabolic rate, and relative brain size. Finally, we encourage integration of mechanistic and evolutionary studies of defensive spines and suggest future avenues of research in the biomechanics, evolution, and behavior of spines and spiny organisms.

The evolution and ecology of multiple antipredator defences

“…In poison frogs, specialized diets may facilitate the evolution of aposematism (Santos et al, 2003), and conspicuous coloration is correlated with large body size (Hagman & Forsman, 2003). Correlations between defences are also commonly studied as indicators of signal honesty in aposematism (e.g., mushroom coloration, odours, and toxins; Sherratt et al, 2005; carnivore coloration and noxious secretions; Stankowich et al, 2011; Crofts & Stankowich, 2021), or in terms of trade‐offs between different defences (e.g., defensive behaviour and morphology in scorpions; Van Der Meijden et al, 2013). Macro approaches have also been used to uncover the evolutionary sequence of defence adaptations.…”

The moment of tooth: rate, fate and pattern of Pacific lingcod dentition revealed by pulse-chase

“…There are good functional reasons for this. The small, slender teeth that catch and grab soft tissue resist bending poorly and should fracture at a high rate [9,12]. A sharp dental battery must be replaced often-in our data small, sharp teeth are in place for just a few days.…”

“…However, we do not know whether it is a response to a single tooth being broken. An advantage of continuously replacing teeth is that they can occupy a risky region of the wear resistance ←→ performance continuum [9,12].…”

Macroevolutionary Constraint and Selection on Anti-Bat Moth Tails

“…Elaborate traits provide a lens through which we can investigate opposing evolutionary pressures, as they are most likely to have emerged via strong selection. From the Narwal’s tusk [1] to the peacock’s train [2] to the porcupine’s quills [3], elaborate traits often play a role in high-stakes inter or intraspecific interactions – either to win potential mates or to evade potential predators. Due to their complex, conspicuous nature, these traits are commonly assumed to come with tradeoffs [4].…”