title: Cheaters must prosper: reconciling theoretical and empirical perspectives on cheating in mutualism.
abstract: Cheating is a focal concept in the study of mutualism, with the majority of researchers considering cheating to be both prevalent and highly damaging. However, current definitions of cheating do not reliably capture the evolutionary threat that has been a central motivation for the study of cheating. We describe the development of the cheating concept and distill a relative-fitness-based definition of cheating that encapsulates the evolutionary threat posed by cheating, i.e. that cheaters will spread and erode the benefits of mutualism. We then describe experiments required to conclude that cheating is occurring and to quantify fitness conflict more generally. Next, we discuss how our definition and methods can generate comparability and integration of theory and experiments, which are currently divided by their respective prioritisations of fitness consequences and traits. To evaluate the current empirical evidence for cheating, we review the literature on several of the best-studied mutualisms. We find that although there are numerous observations of low-quality partners, there is currently very little support from fitness data that any of these meet our criteria to be considered cheaters. Finally, we highlight future directions for research on conflict in mutualisms, including novel research avenues opened by a relative-fitness-based definition of cheating.
authors.affiliation: Department of BioSciences, Rice University, Houston, TX, 77005, USA.|Wissenschaftskolleg zu Berlin, Institute for Advanced Study, 14193, Berlin, Germany.|Department of Entomology, Washington State University, Pullman, WA, 99164, USA.
authors.forename: Emily I
authors.initials: EI
authors.lastname: Jones
authors.affiliation: Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3G5, Canada.
authors.forename: Michelle E
authors.initials: ME
authors.lastname: Afkhami
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA, 19104, USA.
authors.forename: Erol
authors.initials: E
authors.lastname: Akçay
authors.affiliation: Department of Ecology & Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Judith L
authors.initials: JL
authors.lastname: Bronstein
authors.affiliation: Institute of Biology, University of Neuchâtel, CH-2000 Neuchâtel, Switzerland.
authors.forename: Redouan
authors.initials: R
authors.lastname: Bshary
authors.affiliation: Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3G5, Canada.
authors.forename: Megan E
authors.initials: ME
authors.lastname: Frederickson
authors.affiliation: Department of Biology, University of Illinois, Urbana, IL, 61801, USA.
authors.forename: Katy D
authors.initials: KD
authors.lastname: Heath
authors.affiliation: Department of Biology, University of Mississippi, University, MS, 38677, USA.
authors.forename: Jason D
authors.identifier: http://orcid.org/0000-0003-2338-8442
authors.initials: JD
authors.lastname: Hoeksema
authors.affiliation: Department of Biology, Skidmore College, Saratoga Springs, NY, 12866, USA.
authors.forename: Joshua H
authors.initials: JH
authors.lastname: Ness
authors.affiliation: Department of Molecular, Cell and Biomedical Sciences, University of New Hampshire, Durham, NH, 08624, USA.
authors.forename: M Sabrina
authors.initials: MS
authors.lastname: Pankey
authors.affiliation: Department of Biology, University of California, Riverside, CA, 92521, USA.
authors.forename: Stephanie S
authors.initials: SS
authors.lastname: Porter
authors.affiliation: Department of Biology, University of California, Riverside, CA, 92521, USA.
authors.forename: Joel L
authors.initials: JL
authors.lastname: Sachs
authors.affiliation: Department of Plant Biology, Michigan State University, East Lansing, MI, 48824, USA.
authors.forename: Klara
authors.initials: K
authors.lastname: Scharnagl
authors.affiliation: Department of Plant Biology, Michigan State University, East Lansing, MI, 48824, USA.
authors.forename: Maren L
authors.identifier: http://orcid.org/0000-0002-4274-8928
authors.initials: ML
authors.lastname: Friesen
keywords: Ant-plant; cleaner fish-client; cooperation; fig-fig wasp; fitness conflict; legume-rhizobia; nectar larceny; partner quality; plant-mycorrhizae; yucca-yucca moth