The roles of sex and morphology in burrowing depth of Iberian spadefoot toads in different biotic and abiotic environments

Hiding behavior is key for most animals’ fitness, but it entails costs that must be balanced with benefits. Most research on this potential trade-off focuses on hiding time. However, other features that might mirror an actual energy investment on hiding behavior, such as burrowing depth, have long been neglected. In this work, we examined energy-demanding burrowing behavior of Iberian spadefoot toads (Pelobates cultripes), which hide in burrows they dig with the aid of a hard spade on each hindlimb. Namely, we tested whether toads increased burrowing depth as a response to soil dryness and predator kairomones, in search for subterranean humidity and predator avoidance, respectively. To do so, we measured burrowing depth of adult toads under three different treatments in a repeated-measures design: damp sand, dry sand and sand with boar predator kairomones. We also checked potential effects of sex and morphology (snout–vent length, body mass, hindlimb length and spade length) on burrowing depth. Morphometric variables measured were not good predictors of burrowing depth: Mainly, body mass showed a negative relationship with burrowing depth. However, despite their greater body mass, females burrowed deeper than males in the damp sand treatment. Albeit, contradicting our hypothesis, males did not respond to the presence of predator kairomones, while females reduced their burrowing depth. This result could be a consequence of predator-induced stress affecting burrowing ability. Also, both females and males burrowed shallower in the dry-sand treatment than in the others, which could be due to substrate instability or to dehydration.FJZ-C was supported by a Juan de la Cierva-Formacion contract by the Spanish Ministerio de Economía, Industria y Competitividad (MINECO)