Cross-sensory modulation in a future top predator, the young Nile crocodile

Abstract

Animals routinely receive information through different sensory channels, and inputs from a modality may modulate the perception and behavioural reaction to others. In spite of their potential adaptive value, the behavioural correlates of this cross-sensory modulation have been poorly investigated. Due to their predator life, crocodilians deal with decisional conflicts emerging from concurrent stimuli. By testing young Crocodylus niloticus with sounds in the absence or presence of chemical stimuli, we show that (i) the prandial (feeding) state modulates the responsiveness of the animal to a congruent, i.e. food-related olfactory stimulus, (ii) the prandial state alters the responsiveness to an incongruent (independent of food) sound, (iii) fasted, but not sated, crocodiles display selective attention to socially relevant sounds over noise in presence of food odour. Cross-sensory modulation thus appears functional in young Nile crocodiles. It may contribute to decision making in the wild, when juveniles use it to interact acoustically when foraging.

Crocodilians are promising intermediate model organisms for comparative perception research

“…Upon hearing recordings of contact calls of same-aged conspecifics, young black caimans (Melanosuchus niger) gradually swim in the general direction of the loudspeaker (Vergne, Aubin, Taylor, & Mathevon, 2011). The prandial (feeding) state of young crocodilians appears to affect their response to contact calls, which further supports the contextual connection to foraging: In the presence of a food odor, juvenile Nile crocodiles spend more time orienting toward playbacks of contact calls compared with a noise stimulus only if they have not eaten in 2 days; sated juveniles do not show this discrimination but are more likely to explore their surroundings independent of playback type (Chabrolles, Coureaud, Boyer, Mathevon, & Beauchaud, 2017). Adult crocodilians attend to hatchling and juvenile contact calls (Vergne et al, 2012) and can probably perceive the body size of the producers.…”

“…But whether crocodilians can actually locate food by smell has received little experimental evaluation. Under laboratory conditions, juvenile Nile crocodiles stayed closer to an olfactory meat stimulus compared with a water control if they had not eaten in 2 days (Chabrolles et al, 2017). In a two-choice task, captive adult American alligators were presented with two paper bags-one containing meat, the other more paper (Scott & Weldon, 1990).…”

Chemiosemiosis and Complex Patterned Signals: A Chemosemiotic Hypothesis of Language Evolution

“…Despite being the only reptile group without a VNO, olfaction is still an important sensory modality for crocodiles. Indeed, a study by Chabrolles et al (2017) revealed that Nile crocodiles Crocodylus niloticus rely on both olfaction and vision during appetitive gustatory behaviour and employ cross-sensory modulation when selecting food sources. This means that the visual sign must match the olfactory sign for a food source to be considered edible and consummatory behaviour to be stimulated.…”