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

Abstract

Summary1. 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.

The role of skill in animal contests: a neglected component of fighting ability

“…body size, weapon size) have been heavily studied, these traits are often relatively fixed and thus do not directly account for the interactive nature of fighting. Furthermore, the importance of these traits will vary across species and thus it is still not clear whether there could be general traits that differentiate winners from losers across diverse species of fighting animals [3]. Here we argue that how skilfully an individual fights is driven by both intrinsic and extrinsic factors associated with fighting.…”

“…But given that RHP is already known to be influenced by several other traits [3] how important is skill likely to be in influencing the outcome of fights? As noted above, at present there are very few studies of fighting skill in animals [34,56] and only one of these [34] looks at the effect of motor patterns on outcomes.…”

Using knowledge from human research to improve understanding of contest theory and contest dynamics

“…Or do animals make even more complex decisions during contests, by both assessing their opponent and comparing this assessment with what they know about their own current fighting ability (mutual assessment models; [6])? Understanding which assessment strategies animals use, whether they modify their assessment strategies in different contexts, and the factors individuals use to make decisions within contests are some of the most-discussed questions in the contest literature [5,[7][8][9][10]. Much of this discussion revolves around the extent to which animals vary their strategies (e.g.…”

Evolutionary Game Theory in Biology

“…Over the years, a great number of studies of animal contests have accumulated, and overall it is the case that winners differ from losers in morphological and physiological characteristics that might indicate fighting ability, with higher values for winners (Vieira and Peixoto, 2013). It is also established that contestants generally acquire information, both in the current contest and from previous contests, and use this in deciding whether to withdraw or persist (Hsu et al, 2006), so some assessment of fighting abilities is widespread.…”