“Considerations used by desert isopods to assess scorpion predation risk”

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Moshe Zaguri, Yaara Zohar, and Dror Hawlena (Nov 2018)

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Assessing the risk assessment – which predatory cues and in what context will justify an anti-predatory response?

How do desert isopods manage fear?

A desert isopod parent with its siblings outside their burrow.
(Credit: Moshe Zaguri)

“The world is a dangerous place to live,” wrote Albert Einstein. This is most likely what desert isopods think every morning when leaving the safety of their family burrows to forage in a landscape full of threats. Trying to reveal how prey distinguish between safe and dangerous areas is a major experimental challenge because it requires inferring sensory abilities and cognitive decisions from their behavioral reactions. In this paper, Zaguri, Zohar, and Hawlena from the Ecostress lab at the Hebrew University of Jerusalem have explored how isopods assess the threat of golden Israeli scorpion predation in the central Negev desert. They introduced different combinations of signals that scorpions leave behind to the isopod natural habitat, and meticulously measured the isopods’ behavioral responses to these signals upon first encountering them. Isopods can identify the smell of a scorpion but respond to them only when this smell is associated with other odors or excavated soil mounds that imply an active scorpion burrow. This risk assessment process is efficient because golden scorpions hunt isopods only from the depth of the burrow. Simultaneous presence of different predator cues provoked graded defense reaction, possibly reflecting an additive increase in risk estimation. Our results suggest that isopods can modify their risk estimation based on the context in which the cue is perceived.


Desert isopod (Hemilepistus reaumuri) foraging for soil crust at dawn in the Negev desert.
(Credit: Moshe Zaguri)

Abstract

Animals adjust behaviors to balance changes in predation risk against other vital needs. Animals must therefore collect sensory information and use complex risk assessment process that estimates risks and weigh costs and benefits entailed in different reactions. Studying this cognitive process is challenging, especially in nature because it requires inferring sensory abilities and conscious decisions from behavioral reactions. Our goal was to address this empirical challenge by implementing psychophysical principles to field research that explores considerations used by desert isopods (Hemilepistus reaumuri) to assess the risk of scorpions that hunt exclusively from within their burrows. We introduced various combinations of chemical and physical cues to the vicinity of isopod burrows and recorded their detailed reactions upon first encountering the cues. The isopods reacted defensively to scorpion odor but only when accompanied with excavated-soil or other odors typically found near scorpion burrows. Isopods also reacted defensively to piles of excavated soil without scorpion olfactory cues, suggesting that isopods take precautions even against physical disturbances that do not necessarily reflect predator activity. Simultaneous presence of different cues provoked graded responses, possibly reflecting an additive increase in risk estimation. We conclude that wild isopods use defensive reactions toward environmental signals only when the integrated perceptual information implies an active scorpion burrow, or when they lack data to refute this possibility.