Contextualising the bizarre: The integrated functioning of rib puncture as an antipredator defence in the Iberian ribbed newt (Pleurodeles waltl)

Abstract

Numerous prey traits are the result of the pervasive evolutionary pressure imposed by predators. Mirroring their fundamental role in the fitness of prey, some antipredator defences can evolve into elaborate strategies. Such is the case of the Iberian ribbed newt (Pleurodeles waltl), a semiaquatic urodele that inhabits multiple types of inland waterbodies in central and southern Iberian Peninsula and north‐western Africa. It possesses sharp, protractile ribs, which can thwart predators by emerging through skin ‘warts’ they pierce, becoming impregnated with the toxicants these warts produce, and making the newts difficult to swallow. Plus, the orange colour of these warts contrasts with the predominantly dull dorsum. In this work, I studied the interactions between the number of these warts, the saliency of wart colour against dorsum colour of each individual (i.e., the difference in colour between the warts and the dorsum), rib response time (i.e., the time needed for the ribs to emerge in response to a standardised stimulus), body size, and locomotor performance in males and females in either their aquatic or terrestrial stage. I also conducted a field experiment to determine whether predators more frequently attacked plasticine models with conspicuous or inconspicuous warts. I found that wart colour saliency functions as a decoy, attracting predator attacks towards this well‐protected body part. Plus, many of the antipredator defences studied, namely the number of warts, their colour saliency, rib response time, body size, and locomotor performance, were interrelated. Accordingly, more salient warts indicated a faster rib response, suggesting that these defences are coordinated with each other. Plus, locomotion was considerably slower in the terrestrial than in the aquatic stage. Moreover, warts were more salient, and thus more efficient attracting predator attacks, in newts in the slower terrestrial stage. However, rib response was faster in the aquatic stage, which coincides with the newt's activity peak, and therefore with the height of its conspicuousness to predators. Remarkably, faster newts display less salient warts and a slower rib response, which suggests a trade‐off between both defences. Nonetheless, some of these trends are reversed in females, among which faster individuals also display a faster rib response. This could be a likely consequence of reduced predation pressure. These results further the understanding of how prey integrate and tune multiple antipredator defences according to factors that influence predation pressure, such as sex and life stage.

Larval newts from turbid and transparent waterbodies exhibit different morphological and behavioural traits

“…Thus, the bilateral sources of white light were filtered by white polyester before being cast on the aquarium, and uncontrolled light and shades were prevented. An image of this setup is available in Figure S2 in Zamora‐Camacho (2023). Before taking the photos, white balance was calibrated to a white sheet of paper.…”

Morphological Correlates of Locomotion in the Aquatic and the Terrestrial Phases of Pleurodeles waltl Newts from Southwestern Iberia

“…In both stages, these newts are subjected to a strong pressure by a wide array of predators (birds such as Ardea purpurea, Athene noctua, Ciconia ciconia, Milvus migrans, Neophron percnopterus, or Nycticorax nycticorax, mammals such as Lutra lutra, Rattus norvegicus, or Sus scrofa; or snakes such as Natrix maura; [51]). Despite being equipped with diverse antipredator strategies [52], its primary defense in both stages is an attempt to escape the threat by means of a quick flight, either by crawling or swimming [51].…”