Caribbean cleaning gobies prefer client ectoparasites over mucus

If cooperation often involves investment, then what specific conditions prevent selection from acting on cheaters that do not invest? The mutualism between the Indo-Pacific cleaner wrasse Labroides dimidiatus and its reef fish clients has been a model system to study conflicts of interest and their resolution. These cleaners prefer client mucus over ectoparasites – that is, they prefer to cheat – but punishment and partner switching by clients enforce cooperative behaviour by cleaners. By contrast, clients of Caribbean cleaning gobies (Elacatinus spp.) do not to use punishment or partner switching. Here, we test the hypothesis that the behavioural differences between these two cleaner fish systems are caused by differences in cleaner foraging preferences. In foraging choice experiments, we offered broadstripe cleaning gobies Elacatinus prochilos client-derived parasitic isopods, client mucus and a control food item. The cleaning gobies significantly preferred ectoparasites over mucus or the control item, which contrasts with cleaner wrasses. We propose that the low level of cleaner–client conflict arising from cleaning goby foraging preferences explains the observed lack of strategic partner control behaviour in the clients of cleaning gobies

"Fair” outcomes without morality in cleaner wrasse mutualism

Baumard et al. propose a functional explanation for the evolution of a sense of fairness in humans: Fairness preferences are advantageous in an environment where individuals are in strong competition to be chosen for social interactions. Such conditions also exist in nonhuman animals. Therefore, it remains unclear why fairness (equated with morality) appears to be properly present only in human

Pairs of cleaner fish prolong interaction duration with client reef fish by increasing service quality

We present field experiments showing that levels of cooperation quantitatively predict the duration of interactions between the cleaner wrasse and its reef fish clients. Our study contrasts the general assumption that cooperating is a discrete decision, lacking a time dimension that would allow for continuous rather than discrete decisions. Our results precisely fit the predictions of a recent model that attempted to increase biological validity through the incorporation of a time component in cooperative interaction

Variable responses of hawkmoths to nectar-depleted plants in two native Petunia axillaris (Solanaceae) populations

Pollination success of deceptive orchids is affected by the density and distribution of nectar providing plant species and overall plant density. Here we extended the framework of how plant density can affect pollination to examine how it may promote the success of plant intraspecific cheaters. We compared hawkmoth behaviour in two native populations of Petunia axillaris, where we simultaneously offered rewarding and manually depleted P. axillaris. We asked whether pollinator foraging strategies change as a function of plant density and whether such changes may differentially affect nectarless plants. We observed the first choice and number of flowers visited by pollinators and found that in the dense population, pollinators visited more flowers on rewarding plants than on nectar-depleted plants. In the sparse population, such discrimination was absent. As we found no differences in nectar volume between plants of the two populations, the observed differences in plant density may be temporal. We reason that if differences were more permanent, an equivalent of the remote habitat hypothesis prevails: in a sparse population, cheating plants benefit from the absence of inter- and intraspecific competitors because pollinators tend to visit all potential resources. In a denser population, a pollinator's optimal foraging strategy involves more selectivity. This would cause between-plant competition for pollinators in a pollinator-limited context, which applies to most hawkmoth-pollinated systems. We propose that nectar-provisioning of plants can be density-dependant, with cheaters able to persist in low density area

The reputation of punishers

Punishment is a potential mechanism to stabilise cooperation between self-regarding agents. Theoretical and empirical studies on the importance of a punitive reputation have yielded conflicting results. Here, we propose that a variety of factors interact to explain why a punitive reputation is sometimes beneficial and sometimes harmful. We predict that benefits are most likely to occur in forced play scenarios and in situations where punishment is the only means to convey an individual's cooperative intent and willingness to uphold fairness norms. By contrast, if partner choice is possible and an individual's cooperative intent can be inferred directly, then individuals with a nonpunishing cooperative reputation should typically be preferred over punishing cooperators