Body armour guards against dehydration, not just predators

Introduction: Research by Chris Broeckhoven (UAntwerp) reveals function of lizards’ scales.

Crocodiles, armadillos, turtles and many other animals are equipped with scales -a kind of body armour. It is generally accepted that the main purpose of this shield is to protect them from predators. Research at UAntwerp has shed a different light on this, however. “For lizards, in particular, we found that scales are linked to the availability of water in the habitat,” says Chris Broeckhoven.

Many animals have a type of body armour. This protection can take various forms: there is body armour with and without spines, and sometimes it consists of osteoderms, which are hard, bony plates located in the skin under the scales. It is often assumed that these different sorts of body armour have a protective function, meaning the animal in question cannot - or at least not so easily - fall victim to a predator.

Predation pressure

“But there is no hard evidence for this theory,” says biologist Chris Broeckhoven , affiliated with the Functional Morphology research group at the University of Antwerp. Together with colleagues from the VUB and from universities in the United States and South Africa, he carried out extensive research into the body armour of cordyline lizards living in southern Africa.

“There are several species of cordyline lizards living in those regions, with different degrees of body armour. We took micro-CT scans of their body armour and also determined which habitats the animals lived in and what the local situation was with regard to predation pressure, the chance of being attacked by a predator. Southern Africa is home to many species of snake, birds of prey and mongooses, all of which are predators that may regard cordyline lizards as prey.”

Temperature regulation

Broeckhoven and his colleagues made a remarkable observation. “We found no link between the amount of body armour and the local predation pressure. But we did determine that the dryness of the animals' habitat plays a crucial role. Species that live in the semidesert have much more body armour than species living in subtropical areas or in the mountains. Our conclusion is that body armour probably serves to prevent excessive water loss. In dry areas, body armour can certainly provide animals with a great advantage.”

The research has now been published in the scientific journal Proceedings of the Royal Society B. Meanwhile, Broeckhoven and his colleagues are preparing for the next phase: “In the autumn, we want to start testing whether body armour really does stop water loss. We also want to explore the vascular canals in the bony plates of the armour in more depth. Blood flows through those bony plates, which indicates they may also play a role in the animals’ temperature regulation.”

Broeckhoven, C., El Adak, Y., Hui, C., Van Damme, R. & Stankowich T. (2018) On dangerous ground: the evolution of body armour in cordyline lizards. Proceedings of the Royal Society B: Biological Sciences.