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Upon arrival at a carcass, the deutonymphs alight and moult into adults, which then reproduce. carabi travels as sexually immature deutonymphs on the burying beetle, and derives no nourishment directly from its host while it is on board ( Wilson and Knollenberg, 1987). Wilson, 1983 Schwarz et al., 1998), and it is the focus of this study. The Poecilochirus carabi species complex is the most salient and common of these mite species (e.g. Within a week of hatching, the larvae disperse away from the scant remains of the carcass to pupate, while adults fly off – often to breed again.Īdult burying beetles carry up to 14 species of mites, which also breed on carrion and which use the burying beetle as a means of transport between breeding opportunities. The larvae crawl to the carcass and feed themselves on the edible nest, where they are also fed and defended by both parents. During carcass preparation, beetle eggs are laid in the surrounding soil and then hatch within 3–4 days. The beetles also reduce competition with rival species for the resources on the dead body by smearing the flesh in antimicrobial exudates, consuming eggs laid by rival insects and concealing the body below ground ( Chen et al., 2020 Duarte et al., 2018 Scott, 1998). A pair of beetles works together to convert the carcass into an edible carrion nest for their larvae by removing any fur or feathers, and rolling the meat into a ball. Our experiments focus on burying beetles ( Nicrophorus vespilloides), which use the dead body of a small vertebrate to breed upon ( Scott, 1998). Specifically, we determine how temperature and partner density interact with the presence of a third party enemy species to influence the likelihood that a phoretic organism can be induced within a single generation to become a protective mutualist. Here we investigate how biotic and abiotic stressors combine to induce the context-dependent expression of a protective mutualism.

Nor is it well understood whether the extent of mutualism is density-dependent ( Hoeksema and Bruna, 2015 Palmer et al., 2015). In particular, it is unclear how different biotic and abiotic factors combine to influence the expression of a mutualism, especially when conditions vary locally. The stressor can be biotic ( Ashby and King, 2017 Clay, 2014 Ewald, 1987 Lively et al., 2005 Schwarz and Müller, 1992) or abiotic ( Corbin et al., 2017 Engl et al., 2018 Hoang et al., 2019).Īlthough the adaptive evolution of mutualisms has been studied in detail, the contextual factors that drive equivalent variation in the expression of mutualisms on an ecological timescale are relatively less well understood ( Chamberlain et al., 2014 Jaenike et al., 2010 Hoeksema and Bruna, 2015), especially for protective mutualisms ( Hopkins et al., 2017 Palmer et al., 2015). 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 become a protective mutualist upon exposure to an environmental stressor ( Fellous and Salvaudon, 2009 Lively et al., 2005 Hopkins et al., 2017 Rafaluk-Mohr et al., 2018). They involve one species defending another species from attack by a third party species, in exchange for some form of reward ( Clay, 2014 Palmer et al., 2015 Hopkins et al., 2017). Protective mutualisms among macro-organisms are both widespread and well-known ( Clay, 2014 Palmer et al., 2015 Hopkins et al., 2017). 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. However, when blowflies breed on the carrion too, mites enhance beetle reproductive success by eating blowfly eggs. We show that mites compete with beetle larvae for food in the absence of blowflies, and reduce beetle reproductive success. 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.

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. Ecological conditions are known to change the expression of mutualisms though the causal agents driving such changes remain poorly understood.