Norway rats (Rattus norvegicus) communicate need, which elicits donation of food.

Abstract

Reciprocal cooperation has been observed in a wide range of taxa, but the proximate mechanisms underlying the exchange of help are yet unclear. Norway rats reciprocate help received from partners in an iterated Prisoner's Dilemma game. For donors, this involves accepting own costs to the benefit of a partner, without obtaining immediate benefits in return. We studied whether such altruistic acts are conditional on the communication of the recipient's need. Our results show that in a 2-player mutual food-provisioning task, prospective recipients show a behavioral cascade reflecting increasing intensity. First, prospective receivers reach out for the food themselves, then they emit ultrasonic calls toward their partner, before finally showing noisy attention-grabbing behaviors. Food-deprived individuals communicate need more intensively than satiated ones. In return, donors provide help corresponding to the intensity of the recipients' communication. This indicates that rats communicate their need, which changes the helping propensity of potential donors. Communication of need and corresponding adjustment of cooperation may be a widespread proximate mechanism explaining the mutual exchange of services between animals. (PsycINFO Database Record

The smell of hunger: Norway rats provision social partners based on odour cues of need

“…Focal rats started to pull earlier for the stooge if they received odour from a hungry rather than from a satiated rat (X 2 = 413.5; p < 0.001; mean latencies for hungry rats: 29 s; for satiated rats: 85 s; N = 16; Fig 2), even when excluding the outlier (X 2 = 191.93; p < 0.001; mean latencies for hungry rats: 29 s; for satiated rats: 63 s; N = 15; outlier defined as value exceeding mean + (SD × 2)), suggesting that they assess the hunger status of a partner using olfactory cues alone. An enhanced propensity to donate food to hungry as compared with satiated partners has been identified also in previous studies using the same setup, in which the hungry or satiated partners were located in the same cage as the test subject [6,13]. One might argue that olfactory cues emitted by hungry rats could lead to increased general agitation by the focal rat, thereby resulting in higher activity and consequently earlier pulling.…”

“…One might argue that olfactory cues emitted by hungry rats could lead to increased general agitation by the focal rat, thereby resulting in higher activity and consequently earlier pulling. However, rats also pull earlier for cooperative than for defective partners [12,13,17,19,24], and the latency to pull correlates negatively with pulling frequency, suggesting that this latency indeed represents the helping motivation of the focal subjects [6,18].…”

“…The propensity of an animal to cooperate with a conspecific should thus increase when the benefit for the partner is high, while the costs for the helpful individual are low [5]. Animals show need, for instance, for food, by solicitation, which increases the propensity to receive help [6]. Solicitation, for example, by begging behaviour of young vertebrates, frequently involves costly auditory and visual signals [7].…”

“…Solicitation, for example, by begging behaviour of young vertebrates, frequently involves costly auditory and visual signals [7]. When adult animals cooperate, for example, when individuals are close to a desirable resource but unable to access it, prospective recipients may demonstrate their motivation to get the resource by reaching towards it or by vocalizing (for example, the work by Schweinfurth and Taborsky, the work by Burkart and colleagues, the work by Cronin and colleagues, the work by Yamamoto and colleagues, and the work by Melis and colleagues [6,[8][9][10][11]). However, vocalisation and gestures may not necessarily reflect the relative need of the recipient honestly but might instead be used to manipulate a potential donor into helping, for example, by attempting to attract attention of the conspecific [11], threaten it [12], or pretend unwarranted need [13], which may reflect dishonesty [14,15] (see the work by Riehl and Frederickson [16] for review).…”

“…Thereby, rats are sensitive to the quality of help they received [18], and they accept higher costs when providing food to a hungry partner in weak condition than to a well-fed one [13]. When rats are able to donate food to a partner in an experimental task, prospective receivers show solicitation behaviours, including reaching toward the desired food, calling in the ultrasonic frequency range, and trying to catch the attention of the donor [6]. These behaviours increase the partner's propensity to help.…”