RESEARCH ARTICLE Temperature stress induces mites to help their carrion beetle hosts by eliminating rival blowflies Syuan-Jyun Sun1,2*, Rebecca M Kilner1 1Department of Zoology, University of Cambridge, Cambridge, United Kingdom; 2Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei, Taiwan Abstract Ecological conditions are known to change the expression of mutualisms though the causal agents driving such changes remain poorly understood. Here we show that temperature stress modulates the harm threatened by a common enemy, and thereby induces a phoretic mite to become a protective mutualist. Our experiments focus on the interactions between the burying beetle Nicrophorus vespilloides, an associated mite species Poecilochirus carabi and their common enemy, blowflies, when all three species reproduce on the same small vertebrate carrion. We show that mites compete with beetle larvae for food in the absence of blowflies, and reduce beetle reproductive success. However, when blowflies breed on the carrion too, mites enhance beetle reproductive success by eating blowfly eggs. High densities of mites are especially effective at promoting beetle reproductive success at higher and lower natural ranges in temperature, when blowfly larvae are more potent rivals for the limited resources on the carcass. Introduction Protective mutualisms among macro-organisms are both widespread and well-known (Clay, 2014; Palmer et al., 2015; Hopkins et al., 2017). They involve one species defending another species *For correspondence: from attack by a third party species, in exchange for some form of reward (Clay, 2014;
[email protected] Palmer et al., 2015; Hopkins et al., 2017). Theoretical analyses predict that mutualisms like this can evolve when a commensal or mildly parasitic species, that lives in or upon its host, is induced to Competing interests: The become a protective mutualist upon exposure to an environmental stressor (Fellous and Salvaudon, authors declare that no 2009; Lively et al., 2005; Hopkins et al., 2017; Rafaluk-Mohr et al., 2018).