Mutualistic interactions with phoretic mites Poecilochirus carabi expand the realised thermal niche of the burying beetle Nicrophorus vespilloides

Mutualisms are so ubiquitous, and play such a key role in major biological processes, that it is important to understand how they will function in a changing world. Here we test whether mutualisms can help populations to persist in challenging new environments, by focusing on the protective mutualism between burying beetles Nicrophorus vespilloides and their phoretic mites (Poecilochirus carabi). Our experiments identify the burying beetles fundamental thermal niche and show that it is restricted by competition with blowfly larvae at higher and lower temperatures (within the natural range). We further demonstrate that mites expand the burying beetles realised thermal niche, by reducing competition with blowflies at lower and higher temperatures, thereby enabling beetles to produce more offspring across a wider thermal range. We conclude that mutualisms can play an important role in promoting survival under novel and adverse conditions, particularly when these conditions enhance the performance of a common enemy.