Winners and losers: a meta-analysis of functional determinants of fighting ability in arthropod contests


  • Marcos C. Vieira,

    1. Departamento de Biologia, Universidade Federal do Ceará, Ceará, Brazil
    Current affiliation:
    1. Programa de Pós-Graduação em Ecologia e Evolução, Departamento de Ecologia, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiás, Brazil
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  • Paulo E. C. Peixoto

    Corresponding author
    • Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Bahia, Brazil
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  1. Many game-theoretical models assume that the outcome of agonistic interactions depends on morphological and physiological asymmetries between rivals (the RHP-asymmetry hypothesis). However, some empirical studies fail at identifying traits linked to fighting capacity and are thus unable to support the role of RHP in contest resolution. Perhaps the role of RHP asymmetries in contest resolution is less general than previously thought.
  2. If RHP asymmetries are indeed important, then the actual suite of relevant traits should depend on how costs are accrued during disputes (the functional hypothesis). In species in which contests involve physical contact at some stage, strength-related traits should be important, whereas in species in which disputes do not involve physical contact, persistence-related traits should determine individual fighting ability.
  3. We performed a meta-analysis to investigate the generality of morphological and physiological asymmetries between winners and losers in arthropod contests. We also investigated whether the suite of traits determining fighting ability differs between disputes involving physical contact and disputes in which physical contact is absent.
  4. We show that RHP asymmetries are a general property of contest settlement among arthropods. However, strength-related traits did not have a greater effect than persistence-related traits in determining the settlement of disputes involving physical contact. Neither did persistence-related traits have a greater role in disputes without physical contact than in those involving physical contact.
  5. We provide the first quantitative assessment of the generality and magnitude of RHP asymmetries in contest resolution among arthropods. As different suites of traits were important regardless of the type of dispute, we highlight the importance of considering functionally diverse morphological and physiological traits when trying to identify determinants of fighting ability in agonistic interactions, instead of focusing on a few functionally similar traits.
  6. The assumption of fighting capacity differences among rivals in game-theoretical models was supported by our data. Consequently, models predicting contest settlement based on uncorrelated asymmetries are incompatible with the observation that winners and losers consistently differ in certain attributes.