Proximate causes of variation in dermal armour: insights from armadillo lizards

Abstract

Although it is widely assumed that body armour in animals evolved to thwart predator attacks, assessing the role that predators may play in shaping defensive morphologies has proven to be difficult. Recent studies suggest that body armour might be influenced by additional factors besides predation, and/or even by sexual selection. We investigated variation in dermal armour in 13 populations of armadillo lizards Ouroborus cataphractus, spanning the entire distribution range of the species. We obtained thickness measurements of osteoderms – bony plates embedded in dermal layer of the skin – using micro‐ and nano‐computed tomography. Using these data, we examined the effects of predation pressure/risk and climatic variables on dermal armour variation and addressed sexual and ontogenetic influence. Our results show that climate is the only factor affecting variation in dermal armour. Populations inhabiting more arid environments, characterized by low summer precipitation and mild winter temperatures, are relatively more armoured than those present in less arid environments. In contrast to our expectations, predation pressure or perceived predation risk was not associated with osteoderm thickness. The results of our study support the idea that the evolution of defensive traits might not be driven exclusively by predator–prey interactions, but could be moulded by environmental factors. In particular, we highlight the role of dermal armour as a potentially important mechanism to reduce evaporative water loss in arid environments.

A review of the osteoderms of lizards (Reptilia: Squamata)

“…Thus, the presence, absence, and degree of OD cover for individual species (or individual animals within each species) likely depends on the interplay of, and trade‐offs between, a combination of factors, including environmental factors (e.g. aridity versus humidity, prevalence of shelter and ground cover), the likelihood and type of predator encounters, the ability to capture agile prey, and the danger from conspecific agonists or aggressive prey (Broeckhoven et al ., 2015 , 2017 a ; Broeckhoven et al ., 2018 a ; Broeckhoven, Le Fras Nortier Mouton & Hui, 2018 b ). The selective pressures on ODs expressed in different anatomical regions may also vary, leading to differential regional expression, for example in the cranium (Lacertididae) or the tail [ Platysaurus (Cordylidae)] while lost elsewhere.…”

Sclerite assembly, articulation and protective system of Lower Devonian machaeridians

“…Mounting evidence suggests that defensive trait differentiation may not always evolve solely in response to predation pressures, but instead in concert with habitat‐induced factors (Stankowich & Campbell 2016; Broeckhoven et al . 2018 a , b ).…”

X-ray microtomography in herpetological research: a review

“…Houssaye et al, 2013;Sanger et al, 2013). For example, x-ray microtomography has provided new insight into the ecological drivers of defensive morphologies (Broeckhoven et al, 2018b, c), unravelled the evolutionary history of modern snakes (Yi and Norell, 2015;fig. 6) and ecomorphological relationships among chameleons (Dollion et al, 2017).…”

“…The latter advantage makes the technique particularly suitable for ecological and evolutionary studies that rely on large sample sizes, include protected or rare species, or both (e.g. osteoderms in armadillo lizards; Broeckhoven et al, 2018b). The high demand for three-dimensional imaging of live experimental animals for preclinical research has resulted in the availability of multiple purpose-built in vivo scanners with a rotating gantry design (i.e.…”