Abstract
Evidence that terrestrial gastropods are able to detect chemical cues from their predators is obvious yet scarce, despite the scientific relevance of the topic to enhancing our knowledge in this area. This study examines the influence of cuticular extracts from predacious ground beetles (Carabus auratus, Carabus hispanus, Carabus nemoralis and Carabus coriaceus), and a neutral insect species (Musca domestica) on the shelter-seeking behavior of naive slugs (Deroceras reticulatum). Slugs, known to have a negative phototactic response, were exposed to light, prompting them to make a choice between either a shelter treated with a cuticular extract or a control shelter treated with pure ethyl alcohol. Their behavioral responses were recorded for one hour in order to determine their first shelter choice, their final position, and to compare the percentage of time spent in the control shelters with the time spent in the treated shelters.The test proved to be very effective: slugs spent most of the experiment in a shelter. They spent significantly more time in the control shelter than in the shelter treated with either C. nemoralis (Z = 2.43; p = 0.0151; Wilcoxon matched-pairs signed-ranks test) or C. coriaceus cuticular extracts (Z = 3.31; p<0.01; Wilcoxon matched-pairs signed-ranks test), with a seemingly stronger avoidance effect when presented with C. coriaceus extracts. The other cuticular extracts had no significant effect on any of the behavioral items measured. Although it cannot be entirely excluded that the differences observed, are partly due to the intrinsic properties of the vehicle employed to build the cuticular extracts, the results suggest that slugs can innately discriminate amongst different potential predators and adjust their behavioral response according to the relevance of the threat conveyed by their predator’s chemical cues.
Highlights
Among the most essential needs for organisms, the ability to detect and avoid predators is paramount [1,2] because the consequences of predation are often irretrievable and dramatic for the lifespan – and the fitness – of prey species [3]
There were no significant differences between time spent in the control shelter versus the treated shelter when cuticular extracts of C. auratus, C. hispanus, M. domestica were present or when only a blank Whatman paper was present
When given a choice between the alcohol treatment and a shelter where cuticular extracts from C. auratus, C. hispanus, or M. domestica or a blank Whatman paper was present, the total number of slugs choosing the test shelter and control shelter were similar, as was the total number of slugs found present at the end of the replicates in the control shelter or the shelters that were treated with the previously cited treatments
Summary
Among the most essential needs for organisms, the ability to detect and avoid predators is paramount [1,2] because the consequences of predation are often irretrievable and dramatic for the lifespan – and the fitness – of prey species [3]. Predation is considered to be a major selection force that drives organism evolution [4,5,6] and intervenes in every phase of life by shaping morphology, behavior, ecology and life history traits [2,4,7]. It is to the benefit of prey to be able to assess, at any time, the actual threats posed by predation in order to adequately adjust activity rather than expend large amounts of energy in an attempt to escape a direct attack from a predator. If we consider that chemical senses are the oldest and the most ubiquitous form of sensory perception, it is not surprising that predation risk assessment through olfactory means is so common in aquatic environments [1,11,12]
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