Different responses to reward comparisons by three primate species

Area of Science:

• Behavioral Ecology
• Evolutionary Psychology
• Primate Cognition

Background:

• Cooperative breeding is linked to increased prosocial behaviors, such as food sharing, in many species.
• This prosociality is hypothesized to stem from the interdependence inherent in cooperative breeding systems.
• Previous research suggests cooperative breeders may not react negatively to unequal outcomes due to mate-finding costs.

Purpose of the Study:

• To investigate the response of New World primate species with varying parental care strategies to unequal outcomes.
• To determine if pair-bonding or bi-parental care, in addition to cooperative breeding, influences responses to inequity.
• To validate experimental procedures using a species known to respond to individual contrast.

Main Methods:

• Tested three New World primate genera: a cooperative breeder (Callithrix spp.), a bi-parental care species (Aotus spp.), and a control species (Saimiri spp.).
• Utilized an established inequity paradigm where paired individuals received rewards that sometimes differed.
• Assessed responses to unequal outcomes under both individual and social contrast conditions.

Main Results:

• None of the three tested primate species exhibited negative responses to inequitable outcomes in this experimental setup.
• Saimiri spp. demonstrated a positive response to individual contrast, confirming the validity of the experimental procedure.
• The findings indicate that factors beyond cooperative breeding, such as pair-bonding or bi-parental care, may be influential.

Conclusions:

• The absence of negative reactions to inequity across species suggests that pair-bonding or bi-parental care might shape these behaviors.
• These results challenge the exclusive link between cooperative breeding and tolerance of unequal outcomes in primates.
• Further research across diverse social structures is crucial for understanding the evolution of decision-making and prosociality.