A Shared Food Source Is Not Necessary to Elicit Inequity Aversion in Dogs.

Jim Mcgetrick,Sabrina Ausserwöger,Ingrid Leidinger,Friederike Range,Claudia Attar

doi:10.3389/fpsyg.2019.00413

Jim Mcgetrick, Sabrina Ausserwöger + Show 3 more

Open Access

https://doi.org/10.3389/fpsyg.2019.00413

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Abstract

Cooperative interactions frequently result in the acquisition of resources that have to be shared. Distribution of such resources should be equitable for cooperation to be beneficial. One mechanism thought to maintain cooperation through promotion of equitable reward distribution is inequity aversion, the resistance to inequitable outcomes. Inequity aversion has been demonstrated in many non-human animal species. It is not yet clear whether inequity aversion is limited to situations in which resources are shared; however, a recent study on inequity aversion in dogs, in which reward sources were separated, failed to elicit inequity aversion, hinting at the possible necessity of a shared resource for eliciting inequity aversion. Here, we employed a modified version of the previously used paw task to test the hypothesis that a shared food source is necessary to elicit inequity aversion in dogs. In our study, an experimenter asked pairs of dogs for their paw and rewarded them equally or unequally; however, unlike the standard paw task, the rewards for each dog came from separate food bowls. Dogs displayed the typical basic aversion to inequity despite the lack of a shared food source. These results suggest that a shared food source is not necessary to elicit inequity aversion and that separation of food sources does not explain the recent failure to elicit inequity aversion in dogs. Our findings may also be reflective of the variety of situations in which inequity aversion is potentially applied, the mechanisms underlying inequity aversion in dogs, and the behavioural contexts from which inequity aversion initially evolved.

Highlights

Cooperative interactions among animals frequently result in the acquisition of shared resources
Food expectation and negative contrast were ruled out as all rewards were visible to subjects across all conditions, and subjects’ rewards were downshifted in the inequity and control condition. These results suggest that dogs possess a basic form of inequity aversion and this response appears to be robust, as it has since been replicated in another “paw task” study (Brucks et al, 2016)
The number of combined paw commands and sit commands issued per trial was significantly larger in the Reward inequity (RI) condition compared with that in the Equity test (ET) condition and the No-Reward control (NR) condition (GLMM: RI vs. ET: β = 0.69, S.E. = 0.31, p < 0.001; RI vs. NR: β = 0.39, S.E. = 0.12, p = 0.002)

Summary

Introduction

Cooperative interactions among animals frequently result in the acquisition of shared resources. A cooperative hunt among chimpanzees (Pan troglodytes), wolves (Canis lupus), or lions (Panthera leo) can result in the acquisition of a single carcass (Mech, 1970; Scheel and Packer, 1991; Boesch, 1994, 2002; MacNulty et al, 2014; Gilby et al, 2015) How such shared resources are distributed is not trivial, as individuals can vary in the effort they invest (Scheel and Packer, 1991), the specific roles they play in the hunt (Stander, 1992; Boesch, 2002), and the importance of the contributions they make (Gilby et al, 2015), in acquiring the resource. Initial reports of inequity aversion in primates were controversial due to potential alternative explanations such as food expectation or negative contrast (i.e. reduced performance due to a downshift in reward quality) (Wynne, 2004; Roma et al, 2006; Neiworth et al, 2009); these alternative explanations were ruled out in later studies (van Wolkenten et al, 2007; Brosnan et al, 2010; Hopper et al, 2014; see McGetrick and Range, 2018, for a discussion of the alternative explanations)

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