The Meaning of Jolts by Fish Clients of Cleaning Gobies

Cooperative interactions offer the inherent possibility of cheating by each of the interacting partners. A key challenge to behavioural observers is to recognize these conflicts, and find means to measure reliably cheating in natural interactions. Cleanerfish Labroides dimidiatus cheat by taking scales and mucus from their fish clients and such dishonest cleaning has been previously recognized in the form of whole‐body jolts by clients in response to cleaner mouth contact. In this study, we test whether jolts may be a general client response to cheating by cleaners. We experimentally varied the ectoparasite loads of yellowtail damselfish (Microspathodon chrysurus), a common client of the cleaning goby Elacantinus evelynae, and compared the rates of jolts on parasitized and deparasitized clients. As predicted if jolts represent cleaner cheating, deparasitized clients jolted more often than parasitized clients, and overall jolt rates increased over time as client parasite load was presumably reduced by cleaning activity. Yellowtail damselfish in the wild jolted significantly less frequently than those in captivity, which is consistent with a loss of ectoparasites during capture. Our results suggest that jolts by clients of cleaning gobies are not related to the removal of ectoparasites. Client jolts may therefore be a generally accurate measure of cheating by cleanerfish.     

Self-serving punishment of a common enemy creates a public good in reef fishes

A key challenge for evolutionary biologists is to determine conditions under which individuals benefit from a contribution to public goods [1, 2]. For humans, it has been observed that punishment of free riders may promote contributions [3,?4], but the conditions that lead to stable cooperation based on punishment remain hotly debated [5-8]. Here we present empirical evidence that public goods may emerge as a by-product of self-serving punishment in interactions between coral reef fishes and parasitic saber-tooth blennies that stealthily attack their fish victims from behind to take a bite [9]. We first show that chasing the blenny functions as punishment [10], because it decreases the probability of future attacks. We then provide evidence that in female scalefin anthias, a shoaling species, punishment creates a public good because it increases the probability that the parasite switches to another species for the next attack. A final experiment suggests that punishment is nevertheless self-serving because blennies appear to be able to discriminate between look-alike punishers and nonpunishers. Thus, individuals that do contribute to the public good may risk being identified by the parasite as easy targets for future attacks.     

Interspecific communicative and coordinated hunting between groupers and giant moray eels in the Red Sea

Intraspecific group hunting has received considerable attention because of the close links between cooperative behaviour and its cognitive demands. Accordingly, comparisons between species have focused on behaviours that can potentially distinguish between the different levels of cognitive complexity involved, such as “intentional” communication between partners in order to initiate a joint hunt, the adoption of different roles during a joint hunt (whether consistently or alternately), and the level of food sharing following a successful hunt. Here we report field observations from the Red Sea on the highly coordinated and communicative interspecific hunting between the grouper, Plectropomus pessuliferus, and the giant moray eel, Gymnothorax javanicus. We provide evidence of the following: (1) associations are nonrandom, (2) groupers signal to moray eels in order to initiate joint searching and recruit moray eels to prey hiding places, (3) signalling is dependent on grouper hunger level, and (4) both partners benefit from the association. The benefits of joint hunting appear to be due to complementary hunting skills, reflecting the evolved strategies of each species, rather than individual role specialisation during joint hunts. In addition, the partner species that catches a prey item swallows it whole immediately, making aggressive monopolisation of a carcass impossible. We propose that the potential for monopolisation of carcasses by one partner species represents the main constraint on the evolution of interspecific cooperative hunting for most potentially suitable predator combinations.     

Long-term memory retention in a wild fish species Labroides dimidiatus eleven months after an aversive event

Memory is essential to enhance future survival and reproduction as it helps in storing and retrieving useful information to solve particular environmental problems. However, we lack quantitative evidence on how far animals in the wild can maintain given information for extended periods without reinforcement. Here, we document correlative evidence of cleaner fish Labroides dimidiatus remembering being caught in a barrier net for up to 11 months. In 2015, about 60% of cleaners from one large isolated reef had been used for laboratory experiments and then returned to their site of capture. Eleven months later, 50% of cleaners at the same site showed an unusual hiding response to the placement of the barrier net, in contrast to three control sites where no cleaners had been caught during the last 2 years. The results suggest that a single highly aversive event (i.e., being caught in a barrier net) resulted in cleaners storing long-term crucial information that allowed them to avoid being caught again. Our results further our knowledge of fish cognitive capacities and long-term memory retention.     

From parasitism to mutualism: partner control in asymmetric interactions

Intraspecific cooperation and interspecific mutualism often feature a marked asymmetry in the scope for exploitation. Cooperation may nevertheless persist despite one‐sided opportunities for cheating, provided that the partner vulnerable to exploitation has sufficient control over the duration of interaction. Here we develop a simple, game theoretical model of this form of partner control. We show that as a victim's ability to terminate an encounter increases, selection can favour reduced exploitation, resulting in a switch from parasitism to mutualism. For a given level of control, exploitation is likely to be less intense and the interaction to last longer when there are greater mutualistic benefits to be gained, and when the benefits of cheating are lower relative to the costs inflicted on the victim. Observations of interactions between cleaner‐fish and non‐predatory species of client are shown to match these predictions.     

Cleaner Wrasses Keep Track of the ‘When’ and ‘What’ in a Foraging Task1

In recent years evidence has accumulated that at least some animals can remember the ‘what’, ‘where’ and ‘when’ of personal experiences. Currently, evidence for such ability is taxonomically restricted to birds and mammals. Here, we demonstrate for the first time that cleaner wrasses Labroides dimidiatus are able to remember when they interacted with what after a single event. In nature, cleaners remove ectoparasites from other reef fishes, so‐called clients. Clients are depleted, non‐stationary food patches at the end of an interaction and replenished only after a delay. In our experiments, we presented twelve cleaners every 2.5 min, a choice between two of a total of four plates with different colours and patterns. One plate was always accessible but contained a non‐preferred food item while the other three contained a preferred food item, but allowed a next feeding event only after 5, 10 or 15 min. Thus, to maximise food intake, cleaners had to remember for each choice when they had last interacted with which plate. When confronted with two plates offering preferred food, cleaners showed an overall significant preference for the plate that allowed access during the trial. For six cleaners, the preference was significant. Also, on trials involving the always accessible plate, cleaners discriminated between trials in which they had to eat the non‐preferred food and trials on which they could eat the preferred food. In conclusion, cleaners are able to track the ‘when’ and ‘what’ (or possibly ‘who’) within a biologically meaningful time period.     

Osmotic stress alters the balance between organic and inorganic solutes in flax (Linum usitatissimum)

Flax (Linum usitatissimum) is grown for its oil and its fiber. This crop, cultivated in temperate regions, has seen a renewed interest due to the presence of abundant molecules of interest for many applications. Little information is available about the behavior of flax during osmotic stress; yet this is considered a major stress that causes significant yield losses in most crops. To control the presence of this stress better, flax behavior was investigated following the application of osmotic stress and the response was examined by applying increasing concentrations of PEG 8000. This resulted in the reorganization of 32 metabolites and 6 mineral ions in the leaves. The analysis of these two types of solute highlighted the contrasting behavior between a higher metabolite content (particularly fructose, glucose and proline) and a decrease in mineral ions (especially nitrate and potassium) following PEG treatment. However, this reorganization did not lead to a greater accumulation of solutes, with the total amount remaining unchanged in leaves during osmotic stress.