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Tolerance and reward equity predict cooperation in ravens (Corvus corax).

Massen JJ, Ritter C, Bugnyar T - Sci Rep (2015)

Bottom Line: The ravens, moreover, also paid attention to the resulting reward distribution and ceased cooperation when being cheated upon.Nevertheless, the ravens did not seem to pay attention to the behavior of their partners while cooperating, and future research should reveal whether this is task specific or a general pattern.Given their natural propensity to cooperate and the results we present here, we consider ravens as an interesting model species to study the evolution of, and the mechanisms underlying cooperation.

View Article: PubMed Central - PubMed

Affiliation: University of Vienna, Department of Cognitive Biology, Vienna, Austria.

ABSTRACT
Cooperative decision rules have so far been shown experimentally mainly in mammal species that have variable and complex social networks. However, these traits should not necessarily be restricted to mammals. Therefore, we tested cooperative problem solving in ravens. We showed that, without training, nine ravens spontaneously cooperated in a loose-string task. Corroborating findings in several species, ravens' cooperative success increased with increasing inter-individual tolerance levels. Importantly, we found this in both a forced dyadic setting, and in a group setting where individuals had an open choice to cooperate with whomever. The ravens, moreover, also paid attention to the resulting reward distribution and ceased cooperation when being cheated upon. Nevertheless, the ravens did not seem to pay attention to the behavior of their partners while cooperating, and future research should reveal whether this is task specific or a general pattern. Given their natural propensity to cooperate and the results we present here, we consider ravens as an interesting model species to study the evolution of, and the mechanisms underlying cooperation.

No MeSH data available.


(a) Proportion of trials in which two birds cooperated successfully subsequent to an equal or unequal reward devision after the previous successful cooperation trial, and (b) proportion of trials in which a bird pulled the string after it had received zero, one or two rewards in the previous successful cooperation trial.
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f3: (a) Proportion of trials in which two birds cooperated successfully subsequent to an equal or unequal reward devision after the previous successful cooperation trial, and (b) proportion of trials in which a bird pulled the string after it had received zero, one or two rewards in the previous successful cooperation trial.

Mentions: The experimenter always placed 1 piece of cheese on both ends of the feeding platform to allow both collaborators to retrieve one piece after cooperating. However, sometimes one individual would quickly take both rewards after a successful cooperation, leaving its collaborator without reward. To see whether the birds reacted to the reward distribution after a successful cooperation trial, we analyzed for all trials, after the first successful cooperation trial within a session, what would be the probability that both birds would cooperate successfully again. Therefore, we ran a binomial GLMM with a logit link function on whether a dyad would cooperate (yes/no), and entered the same fixed factors as previous analyses, although now we treated session number as a random variable. In addition, we now entered whether the reward distribution in the previous successful trial was equal (yes/no) as a fixed factor. We found that in the best fitting model only inter-individual tolerance still had a positive effect on the probability that two birds would cooperate successfully (β = 0.107, F = 15.31, d.f.n. = 1, d.f.d. = 889, P < 0.001), whereas all previous significant effects were now not significant anymore, and that indeed the reward equity of the previous successful cooperation trial within a session had a significantly positive effect on the probability that two birds would cooperate successfully (β = 0.804, F = 12.98, d.f.n. = 1, d.f.d. = 889, P < 0.001) (for best fitting model see electronic supplementary materials); i.e., if the reward distribution in the previous successful trial was equal (1/1) the probability of two birds successfully cooperating again was significantly higher than when the reward distribution in the previous successful trial was unequal (2/0) (Fig. 3a). This would suggest that birds that did not receive a reward in the previous successful cooperation trial, are less motivated to cooperate again. Indeed the amount of rewards a bird received in the previous successful cooperation trial (0, 1, or 2) significantly influenced the probability that a bird would pull at all in the next trial (be it cooperative or unsuccessful solitary pulls) (F = 18.03, d.f.n. = 1, d.f.d. = 889, P < 0.001); i.e., birds were significantly less likely to pull when they received no reward in the previous successful cooperation trial then when they had received either 1 or 2 rewards (Fig. 3b). To determine whether the bird that previously got all the food in a trial (i.e. ‘cheated’ in the cooperation) would respond to the declined motivation of its partner, we compared the proportion of ‘cheats’ (i.e., taking both rewards instead of sharing) after a previous cheat with the proportion of cheats in general. We found that after cheating the cheater did not become more fair to get back the motivation of its partner, but instead became even more likely to cheat again (χ2 = 6.79, d.f. = 1, P = 0.009), suggesting that if they had learned anything, then it was how to cheat.


Tolerance and reward equity predict cooperation in ravens (Corvus corax).

Massen JJ, Ritter C, Bugnyar T - Sci Rep (2015)

(a) Proportion of trials in which two birds cooperated successfully subsequent to an equal or unequal reward devision after the previous successful cooperation trial, and (b) proportion of trials in which a bird pulled the string after it had received zero, one or two rewards in the previous successful cooperation trial.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4595729&req=5

f3: (a) Proportion of trials in which two birds cooperated successfully subsequent to an equal or unequal reward devision after the previous successful cooperation trial, and (b) proportion of trials in which a bird pulled the string after it had received zero, one or two rewards in the previous successful cooperation trial.
Mentions: The experimenter always placed 1 piece of cheese on both ends of the feeding platform to allow both collaborators to retrieve one piece after cooperating. However, sometimes one individual would quickly take both rewards after a successful cooperation, leaving its collaborator without reward. To see whether the birds reacted to the reward distribution after a successful cooperation trial, we analyzed for all trials, after the first successful cooperation trial within a session, what would be the probability that both birds would cooperate successfully again. Therefore, we ran a binomial GLMM with a logit link function on whether a dyad would cooperate (yes/no), and entered the same fixed factors as previous analyses, although now we treated session number as a random variable. In addition, we now entered whether the reward distribution in the previous successful trial was equal (yes/no) as a fixed factor. We found that in the best fitting model only inter-individual tolerance still had a positive effect on the probability that two birds would cooperate successfully (β = 0.107, F = 15.31, d.f.n. = 1, d.f.d. = 889, P < 0.001), whereas all previous significant effects were now not significant anymore, and that indeed the reward equity of the previous successful cooperation trial within a session had a significantly positive effect on the probability that two birds would cooperate successfully (β = 0.804, F = 12.98, d.f.n. = 1, d.f.d. = 889, P < 0.001) (for best fitting model see electronic supplementary materials); i.e., if the reward distribution in the previous successful trial was equal (1/1) the probability of two birds successfully cooperating again was significantly higher than when the reward distribution in the previous successful trial was unequal (2/0) (Fig. 3a). This would suggest that birds that did not receive a reward in the previous successful cooperation trial, are less motivated to cooperate again. Indeed the amount of rewards a bird received in the previous successful cooperation trial (0, 1, or 2) significantly influenced the probability that a bird would pull at all in the next trial (be it cooperative or unsuccessful solitary pulls) (F = 18.03, d.f.n. = 1, d.f.d. = 889, P < 0.001); i.e., birds were significantly less likely to pull when they received no reward in the previous successful cooperation trial then when they had received either 1 or 2 rewards (Fig. 3b). To determine whether the bird that previously got all the food in a trial (i.e. ‘cheated’ in the cooperation) would respond to the declined motivation of its partner, we compared the proportion of ‘cheats’ (i.e., taking both rewards instead of sharing) after a previous cheat with the proportion of cheats in general. We found that after cheating the cheater did not become more fair to get back the motivation of its partner, but instead became even more likely to cheat again (χ2 = 6.79, d.f. = 1, P = 0.009), suggesting that if they had learned anything, then it was how to cheat.

Bottom Line: The ravens, moreover, also paid attention to the resulting reward distribution and ceased cooperation when being cheated upon.Nevertheless, the ravens did not seem to pay attention to the behavior of their partners while cooperating, and future research should reveal whether this is task specific or a general pattern.Given their natural propensity to cooperate and the results we present here, we consider ravens as an interesting model species to study the evolution of, and the mechanisms underlying cooperation.

View Article: PubMed Central - PubMed

Affiliation: University of Vienna, Department of Cognitive Biology, Vienna, Austria.

ABSTRACT
Cooperative decision rules have so far been shown experimentally mainly in mammal species that have variable and complex social networks. However, these traits should not necessarily be restricted to mammals. Therefore, we tested cooperative problem solving in ravens. We showed that, without training, nine ravens spontaneously cooperated in a loose-string task. Corroborating findings in several species, ravens' cooperative success increased with increasing inter-individual tolerance levels. Importantly, we found this in both a forced dyadic setting, and in a group setting where individuals had an open choice to cooperate with whomever. The ravens, moreover, also paid attention to the resulting reward distribution and ceased cooperation when being cheated upon. Nevertheless, the ravens did not seem to pay attention to the behavior of their partners while cooperating, and future research should reveal whether this is task specific or a general pattern. Given their natural propensity to cooperate and the results we present here, we consider ravens as an interesting model species to study the evolution of, and the mechanisms underlying cooperation.

No MeSH data available.