Dopamine disruption increases negotiation for cooperative interactions in a fish

Abstract

Humans and other animals use previous experiences to make behavioural decisions, balancing the probabilities of receiving rewards or punishments with alternative actions. The dopaminergic system plays a key role in this assessment: for instance, a decrease in dopamine transmission, which is signalled by the failure of an expected reward, may elicit a distinct behavioural response. Here, we tested the effect of exogenously administered dopaminergic compounds on a cooperative vertebrate's decision-making process, in a natural setting. We show, in the Indo-Pacific bluestreak cleaner wrasse Labroides dimidiatus, that blocking dopamine receptors in the wild induces cleaners to initiate more interactions with and to provide greater amounts of physical contact to their client fish partners. This costly form of tactile stimulation using their fins is typically used to prolong interactions and to reconcile with clients after cheating. Interestingly, client jolt rate, a correlate of cheating by cleaners, remained unaffected. Thus, in low effective dopaminergic transmission conditions cleaners may renegotiate the occurrence and duration of the interaction with a costly offer. Our results provide first evidence for a prominent role of the dopaminergic system in decision-making in the context of cooperation in fish.

Figure 1

The effect of D1 agonist (D1a) and antagonist (D1an), D2 agonist (D2a) and antagonist (D2an) on cleaners’ likelihood to engage in cleaning behaviour measured by (a) the proportion of clients inspected (calculated as the total number of clients inspected/total number of visits) and (b) the mean interaction duration (total time of interaction/total number of interactions); cleaners’ cooperative investment measured by: (c) the proportion of interactions with tactile stimulation events (frequency of clients inspected where tactile stimulation occurred/total number of interactions), (d) the proportion of time cleaners spent providing tactile stimulation (total tactile stimulation duration/total interaction duration); and (e) cleaner wrasse cheating levels measured by the frequency of client jolts per 100 seconds of inspection. Medians and interquartile ranges are shown. Significant values are shown above bars: *<0.05; **<0.01; ***<0.001 and refer to Dunn’s Post-Hoc tests affecting each dopamine treatment against the reference (saline) group, for a total sample size of 10 individuals.