The evolution of cooperative behavior does not necessarily require that animals develop a sense of fairness

A pair of blue-throated macaws (Ara glaucogularis) at Chester Zoo, England. These birds, like most ... [+] parrot species, form strong life-long monogamous pair bonds.(Credit: David Friel / CC BY 2.0)

As anyone who lives with parrots knows, they are very jealous and protective of their mates whether their mate is another parrot or a human. But parrots are not jealous about food. Basically, if one parrot is given a less desirable food reward than its partner gets, there are no temper tantrums which is the typical response to unequal resource distribution seen in great apes (and even in a large number of humans). Apparently, unlike most primates, parrot couples are quite tolerant of inequality.

This was the conclusion reached recently by a team of scientists from theMax Planck Institute for Animal Behaviour, a newly-independent research institution in Germany formerly known as the Max Planck Institute for Ornithology.

A key feature in the evolution of cooperation is a sense of fairness, where individuals are provided rewards that are fair and equitable to avoid future breakdown in cooperation (ref). Humans, even children, show a clear and consistent preference for equal over unequal outcomes (ref), a trait known as inequity aversion. For example, children as young as six years old refuse a reward that is less valuable than that given to a peer (disadvantageous inequity aversion), whereas older children typically refuse a reward that is more valuable than that provided to a peer (advantageous inequity aversion). Social scientists consider disadvantageous inequity aversion to be a universal feature of human behavior (PDF), whilst advantageous inequity aversion is probably influenced strongly by cultural norms.

Scientists think that sensitivity to inequity evolved in parallel with the ability for individuals to cooperate because it helps sustain benefitting from cooperation. Additionally, it has been proposed that species that rely on cooperating with group members may benefit from evaluating the equality of their cooperative payoffs to assess whether to stay with a certain partner, or mate, or to look for a new one to gain better outcomes.

The token-exchange paradigm is a classic tool in animal behavior studies that is used to study fairness. It tests the willingness of an animal to sacrifice its own material pay-offs for the sake of greater equality. In this test, when an experimenter does not equally distribute rewards of equal value between experimental subjects, the study animals may express their displeasure with a variety of responses, ranging from refusing to participate in further tests, throwing the reward at the experimenter or even with a temper tantrum.

A team of scientists trained four species of parrots held by the Max-Planck Comparative Cognition Research Station at Loro Parque in Spain, to trade tokens for food. The researchers were under the leadership of Anastasia Krasheninnikova, a postdoctoral researcher at the Institute whose main research interest is the evolution of cognitive skills, particularly identifying whether these skills may be influenced by different socio-ecological living conditions.

This study was designed to provide data on inequity aversion in species, such as parrots, that are distantly related to primates. It also was designed to provide more data on inequity aversion in long-term monogamous species by testing the reaction to inequity of four parrot species belonging to the Psittacoidea superfamily: blue-throated macaws, Ara glaucogularis; great green macaws, Ara ambiguus; blue-headed macaws, Primolius couloni; and African grey parrots, Psittacus erithacus. These species all form long-term monogamous pair bonds and live in family groups. Both parents provide food to their young and offspring stay with their parents for at least one breeding season.

After the study parrots had been trained to trade tokens (a steel washer) for a food reward (either a sunflower seed or a piece of a walnut), the team of researchers then conducted a series of experiments where two parrots were placed into adjacent compartments and each was asked, in turn, by the experimenter to exchange a token for food. Depending upon the experimental treatment, the parrots were either rewarded unequally (Figure 1A) or equally (Figure1B,C) for their efforts. During the tests, the parrots could easily see each other and the food rewards that each parrot got.

Figure 1. Experimental design showing the test and control conditions. Sunflower seeds are ... [+] low-quality rewards and walnut seeds are high-quality rewards.(Image courtesy of Anastasia Krasheninnikova and colleagues.)

Dr. Krasheninnikova and her collaborators observed how the study parrots reacted when they received a food reward with a differing quality for the same effort (unequal reward; Figure 1A) or when one parrot was expected to work harder than his or her partner for the same reward (unequal effort; Figure 1E). When the study parrots reactions were compared to what was observed for equal treatment for each species (Figure 1BC), Dr. Krasheninnikova and her collaborators saw no differences and they definitely did not see any temper tantrums (data video and Figure 2).

Of course, the study parrots had their own opinions about the study. For example, in the control test (when the neighboring chamber was empty), the two bigger macaw species refused to exchange tokens if a better reward was delivered to the empty enclosure (Figure 1D), whilst the smaller parrot species did not refuse to exchange tokens but took longer to do so (African grey parrots) or longer to accept rewards (blue-headed macaws).

Dr. Krasheninnikova and her collaborators found that the blue-throated macaws apparently became increasingly frustrated with the test procedure, whereas the African grey parrots showed the opposite pattern and escalated their number of exchanges in all conditions during the course of the study. This response might indicate that the grey parrots became so familiar with the exchange procedure that they stopped caring about the rewards and their distribution.

These distinct responses reveal strong species differences in their innate sensitivity to reward quality and their frustration (or motivation) with the token exchange task itself, making comparative studies very difficult to interpret.

Figure 2. (AD) Exchanges across test conditions separately for each species (all test sessions ... [+] combined; EQUL = equal low, EQUH = equal high, UNEQ = unequal, FC = food control, EC = effort control, UNEF = unequal effort). (Anastasia Krasheninnikova et al. | doi:10.1038/s41598-019-52780-8)

This study raises an important question: why arent parrots jealous when their partner gets a better reward for the same effort or when one parrot must work harder for the same reward? The answer, we think, can be summed up in just one word: monogamy. Unlike most mammals, most parrot species form long-term monogamous pair bonds and both parents care for their nestlings.

In contrast, it turns out that in long-term monogamous species that form pair bonds for life and show biparental care, such as parrots, there is a much higher tolerance of inequity, Dr. von Bayern said. In such species, individuals greatly depend on their functioning pair-bond and consequently, disrupting such a valuable bond in order to look for a fairer partner would simply be too costly.

But not all parrot species are monogamous. For example, Eclectus parrots, Eclectus species, and Vasa parrots, Coracopsis species, are polygynandrous, whilst a number of other species are socially cooperative breeders, including the golden parakeet, Guaruba guarouba, New Caledonian parakeet, Cyanoramphus saisseti, the horned parakeet, Eunymphicus cornutus, and the monk (quaker) parakeet, Myopsitta monachus. Testing these species using the token-exchange paradigm could provide important insights into whether inequity aversion is a general trait amongst all parrots or whether it is linked to social organization and species mating system.

This is an important finding because inequity aversion, also termed sense of fairness has been considered an important mechanism in the evolution of cooperative behaviour, Dr. Krasheninnikova said in a press release.

It enables individuals to detect when their partner cheats upon them, e.g. by not sharing food equally or by avoiding effort, and therefore allows them to decide when it pays off to switch to a new cooperation partner.

It is a good strategy only for animals living in societies in which one can switch between cooperation partners easily, such as those of most primates, agreed senior author, zoologist Auguste von Bayern, in a press release.

Social organization plays a strong role in whether an individual can easily switch to a new mate or cooperation partner but how strong is the effect of social organization upon the evolution of cooperation?

Our study adds to the very recent evidence, that inequity aversion is not a general prerequisite for the evolution of cooperation, Dr. von Bayern said in a press release.

Anastasia Krasheninnikova,Dsire Brucks,Nina Buffenoir,Dniel Rivas Blanco,Delphine Soulet&Auguste von Bayern(2019). Parrots do not show inequity aversion, Scientific Reports9:16416 | doi:10.1038/s41598-019-52780-8

See the original post here:
Parrots Aren't Jealous When Their Mate Gets A Better Reward - Forbes