Ethology. 2020;00:1–9. wileyonlinelibrary.com/journal/eth | 1 © 2020 Blackwell Verlag GmbH 1 | INTRODUCTION Perceived risk of predation has a substantial impact on the behavior of individual animals, affecting interactions with conspecifics and heterospecifics, foraging strategies, and investments in territorial defense (Lima, 1998; Lima & Dill, 1990). Behavioral responses to the risk of predation are likely to incur fitness costs, as individuals forgo opportunities for obtaining or holding resources in favor of avoiding danger. From the prey's perspective, minimizing such costs requires that individuals have accurate information on the risk of predation, which is likely to change both spatially and temporally. For many aquatic species, the primary sensory mode by which individuals gather information about their environments is chemo- sensory, and in many aquatic species, exposure to chemical cues such as predator kairomones or conspecific alarm or disturbance cues has been shown to induce behavioral changes in prey (Chivers, Brown, & Ferrari, 2012; Kats & Dill, 1998). For example, in cray- fish, which are common and ecologically important macroinverte- brates in many freshwater systems, predator or alarm cues and/or predator presence have been shown to affect a number of compo- nents of normal behavior. Hazlett and Schoolmaster (1998) found that crayfish of the species Faxonius virilis that detect a threat of predation (chemical cues from snapping turtle) generally cease movement and adopt a “watchful” posture, and Kenison, Weldy, and Williams (2018) reported similar effects on movement and posture in individuals of the rusty crayfish, F. rusticus, exposed to cues from fish and amphibian predators. Hamrin (1987) found that predator presence causes individuals of the noble crayfish Astacus astacus to alter their diel activity patterns. Responses of cray- fish to predator presence may vary with crayfish size: Keller and Received: 2 December 2019 | Accepted: 14 January 2020 DOI: 10.1111/eth.13011 RESEARCH PAPER Perception of alarm cues influences the outcome of shelter competition in crayfish20 Joshua Driscoll | Michael Kola | Lauren Mathews Department of Biology, Worcester Polytechnic Institute, Worcester, Massachusetts Correspondence Lauren Mathews, Department of Biology, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA, 01609. Email: lmathews@wpi.edu Editor: Susan Bertram Abstract The effects of predators on prey populations may significantly alter many aspects of prey biology, including spatial distribution, foraging activities, and social interactions. In aquatic habitats, chemosensation is an important mode of communication and has been shown for many taxa, including crayfish, to be used in detection of predator and/or conspecific alarm cues. Here, we report on an experiment to test the hypoth- esis that detection of alarm cues results in greater individual investment in contests over shelters. We tested this hypothesis through dyadic contests between sex- and size-matched, non-reproductive individuals of Faxonius virilis. We found that crayfish responded to exposure to alarm cues by spending more time inside a shelter. We also report that in contests between pairs in which one crayfish had been exposed to alarm cues and the other had not, exposed individuals were significantly more likely to win ownership of a single shelter. However, we did not detect any differences in the contest parameters we recorded between exposed and unexposed crayfish. These impacts on both individual and social behavior indicate that the presence of predators is likely to have large effects on the distribution and structure of crayfish populations. KEYWORDS agonistic behavior, Faxonius virilis, non-consumptive effects, predation risk