Abstract
Prior research has found that one rat will release a second rat from a restraint in the presence of food, thereby allowing that second rat access to food. Such behavior, clearly beneficial to the second rat and costly to the first, has been interpreted as altruistic. Because clear demonstrations of altruism in rats are rare, such findings deserve a careful look. The present study aimed to replicate this finding, but with more systematic methods to examine whether, and under what conditions, a rat might share food with its cagemate partner. Rats were given repeated choices between high-valued food (sucrose pellets) and 30-s social access to a familiar rat, with the (a) food size (number of food pellets per response), and (b) food motivation (extra-session access to food) varied across conditions. Rats responded consistently for both food and social interaction, but at different levels and with different sensitivity to the food-access manipulations. Food production and consumption was high when food motivation was also high (food restriction) but substantially lower when food motivation was low (unlimited food access). Social release occurred at moderate levels, unaffected by the food-based manipulations. When food was abundant and food motivation low, the rats chose food and social options about equally often, but sharing (food left unconsumed prior to social release) occurred at low levels across sessions and conditions. Even under conditions of low food motivation, sharing occurred on only 1% of the sharing opportunities. The results are therefore inconsistent with claims in the literature that rats are altruistically motivated to share food with other rats.
Highlights
Pro-social behavior has been defined as behavior that produces benefits for another, sometimes even at a cost to the individual (West et al, 2007; Cronin, 2012; Sosnowski and Brosnan, 2019)
The present experiment was designed to replicate and extend some key conditions described by Ben-Ami Bartal et al (2011), in which rats chose between social release and food
The present research focused on two main findings from that study and their related conclusions: (1) rats chose food and social release with similar latencies, and food and social release are valued; and (2) rats willingly share food with their social partner, even if it comes at a cost to the individual
Summary
Pro-social behavior has been defined as behavior that produces benefits for another, sometimes even at a cost to the individual (West et al, 2007; Cronin, 2012; Sosnowski and Brosnan, 2019). In an experiment by Ben-Ami Bartal et al (2011), for example, one rat was restrained in a plastic restraint tube that could be opened by a second rat. Such release permitted the restrained animal to leave the tube and spend the remainder of the 60 min session in the presence of the other rat. Subsequent studies have verified that rats will, under a variety of conditions, respond in ways that release a rat from a restraint (Ben-Ami Bartal et al, 2014; Silberberg et al, 2014; Sato et al, 2015; Schwartz et al, 2017; Hachiga et al, 2018; Hiura et al, 2018; Blystad et al, 2019; Vanderhooft et al, 2019). The basic effect is reliable, having been replicated across different procedures and laboratories, but its core mechanisms remain a matter of debate
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