No evidence for a relationship between breed cooperativeness and inequity aversion in dogs

Abstract

Inequity aversion, the resistance to inequitable outcomes, has been demonstrated in a wide variety of animal species. Inequity aversion was hypothesised to have co-evolved with cooperation but only limited evidence supports this. Dogs provide a suitable model species to test this hypothesis as dogs were previously shown to be inequity averse and dog breeds vary in the extent to which they were selected for cooperativeness. Here, we compared the response of 12 individuals of "cooperative worker" breeds with that of 12 individuals of "independent worker" breeds in the "paw task" previously used to demonstrate inequity aversion in dogs. We also compared the two breed groups' subsequent social behaviours in a food tolerance test and free interaction session. Although subjects in both breed groups were inequity averse, we found no considerable difference between the groups in the extent of the negative response to inequity or in the impact of the inequity on subsequent social behaviours. However, we found differences between the breed groups in the response to reward omission with cooperative breeds tending to work for longer than independent breeds. Additionally, in the free interaction session, individuals of cooperative breeds spent more time in proximity to their partner in the baseline condition than individuals of independent breeds. Overall, our results do not provide support for the hypothesis that inequity aversion and cooperation co-evolved. However, they illuminate potential differences in selection pressures experienced by cooperative worker and independent worker dog breeds throughout their evolutionary history.

Fig 1. Paw task.

The experimenter kneels in front of the two dogs, with a bowl of food, and asks each dog for its paw, before rewarding it, or not, depending on the condition.

Fig 2. Number of times the paw was given on command by cooperative worker (N = 12) and independent worker (N = 12) breeds in each condition of the paw task.

Boxes display the interquartile range, black horizontal bars represent the median, whiskers represent the range of data points within 1.5 times the interquartile range from the upper and lower hinge, and circles represent individual data points; dashed, vertical line separates social and asocial conditions. ET, equity; RI, reward inequity; NR, no-reward.

Fig 3. Duration of co-feeding between subject and partner in the food tolerance test for cooperative worker (N = 10) and independent worker (N = 12) breeds after two conditions of the paw task.

Boxes display the interquartile range, black horizontal bars represent the median, whiskers represent the range of data points within 1.5 times the interquartile range from the upper and lower hinge, and circles represent individual data points. ET, equity; RI, reward inequity.

Fig 4. Duration spent in proximity to the conspecific partner (sec.) in the interaction session after the two social conditions of the paw task, for cooperative worker (N = 12) and independent worker (N = 12) breeds.

Boxes display the interquartile range, black horizontal bars represent the median, whiskers represent the range of data points within 1.5 times the interquartile range from the upper and lower hinge, and circles represent individual data points. ET, equity; RI, reward inequity.

Fig 5. Cumulative incidence of first contact with the experimenter (as proportion of observations) for subjects of cooperative worker (N = 12) and independent worker (N = 12) breeds in the interaction session after both social conditions of the paw task.

Derived from Kaplan-Meier estimates. ET, equity; RI, reward inequity; C, cooperative worker breeds; I, independent worker breeds.