What doesn't kill you might make you stronger: functional basis for variation in body armour

Abstract

Summary1. Predation has been proposed to be a selective agent in the evolution of morphological antipredator strategies in prey. Among vertebrates, one of the morphological traits that evolved multiple times is body armour, including carapaces, thickened keratinized scales and plates of dermal bone. 2. It has been generally assumed that body armour provides protection against a predatory attack; yet, few explicit tests of the hypothesis exist. Cordylidae, a relatively small family of southern African lizards, show considerable variation in the degree of body armour. Hence, this family provides an opportunity to test the hypothesis that body armour serves as protection against predators. 3. Experiments were conducted to test whether the bite forces of four species of mammalian predators were high enough to penetrate the skins of Karusasaurus polyzonus, Namazonurus peersi, Cordylus cordylus and Cordylus macropholis, as well as those of Ouroborus cataphractus individuals originating from three localities that differed in their predator diversity. Furthermore, histological techniques were used to test whether variation in skin toughness was associated with concomitant changes in the degree of epidermal (i.e. b-keratin) and dermal (i.e. osteoderm) armour. 4. The skin toughness values for four out of five cordylid lizards tested in this study were well below the bite forces of the mammalian predators. In contrast, the thick osteoderms in the dermis of O. cataphractus can withstand bites from several mongoose species. However, the significant variation in body armour that is present between the three populations of O. cataphractus does not seem to be related to predator diversity. 5. It is concluded that body armour can serve as protection against predation in O. cataphractus, but that alternative selection pressures, such as thermoregulation or predation by snakes, presumably underlie variation in defensive morphology in the other cordylid lizards.

Trait matching and phylogeny as predictors of predator–prey interactions involving ground beetles

“…Ground beetle and matched prey traits were selected to represent hypothesized limitations in their potential interactions (Table ). These limitations included (1) predator/prey size ratio (measured as body length) which is a commonly used proxy for physical limitation of interactions (Cohen et al., ); (2) predator biting force [estimated from allometries with head and mandibular size (Wheater & Evans, )] that was to match prey cuticular toughness (Broeckhoven et al., ; Wheater & Evans, ); (3) predator mandibular gape, which is related to handling ability and was to match prey body width (Evans & Forsythe, ); and (4) predator eye size that was to match the speed of movement of prey (Bauer & Kredler, ). We also included four predator traits associated with mandibular characteristics hypothesized to relate to prey handling (Acorn & Ball, ; Evans & Forsythe, ), but that were difficult to match to any prey traits.…”

Living in the danger zone: Exposure to predators and the evolution of spines and body armor in mammals

“…The sources and direction of selection on robustness of body armor, however, are complex both inter‐ and intraspecifically (Broeckhoven et al. ). The data presented here allow us to integrate proximate and ultimate explanations of body armor evolution.…”

“…), and the cordylid lizard Ouroborus cataphractus , for example, has more robust dermal armor than close relatives, due to its unique habit of visiting termite colonies far from their nearest retreat site, leaving it more exposed to terrestrial predation (Broeckhoven et al. ). In terrestrial mammals, Stankowich and Caro () found that nearly all species of Bovid in which females carried horns were either (1) highly exposed in their environments (as measured by shoulder height × openness of habitat) and used their horns as antipredator weapons or (b) guarded exclusive territories and fought other females with their horns.…”

Ontogenetic scaling patterns of lizard skin surface structure as revealed by gel‐based stereo‐profilometry

“…), mitigation of water loss (Dmi'el, ) and protection from physical damage (Broeckhoven et al. ). For any of these specific functions, however, the evolution of an ‘optimal’ skin surface would depend on the particular environmental and ecological constraints imposed on the animal (Losos, ; Irschick & Higham, ; Riedel et al.…”