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Bshary, Redouan
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Bshary, Redouan
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Professeur ordinaire
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redouan.bshary@unine.ch
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Voici les éléments 1 - 6 sur 6
- PublicationAccès libreLong‐term memory retention in a wild fish species “Labroides dimidiatus” eleven months after an aversive event(2019-10)
; 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. - PublicationAccès libreThe ecology underlying decision rules of bluestreak cleaner wrasse during client interactions(2017)
En étudiant le labre nettoyeur (Labroides dimidiatus) comme modèle, cette thèse avait pour objectifs : 1) d'étudier les importantes disparités entre les données expérimentales et les prévisions théoriques standard concernant les décisions animales lors d’interactions coopératives; et 2) d’explorer la façon dont les nettoyeurs sont en mesure de facilement identifier et utiliser des repères pertinents pour la prise de décision. Les nettoyeurs participent à des interactions mutualistes avec des poissons de récifs coralliens appelés «clients» qui viennent les visiter dans leur territoire afin de se faire déparasiter. Cependant les nettoyeurs préfèrent se comporter en parasites et tricher en se nourrissant du mucus des clients qui est riche en azote plutôt que de leurs parasites. Par conséquent, pour encourager les nettoyeurs à être coopératifs, les clients utilisent divers mécanismes de contrôle tels que la punition et le changement de partenaire. Ce mutualisme entre nettoyeurs et clients a jusqu'ici fourni de solides preuves empiriques soutenant l’usage de la théorie des jeux évolutifs pour prédire le comportement coopératif.
Dans le chapitre 2, je démontre que les nettoyeurs qui proviennent de récifs caractérisés par une structure sociale complexe surpassent largement les nettoyeurs provenant de récifs caractérisés par une structure sociale simple lors d’expériences classiques de coopération et de cognition. Les récifs « simples » sont caractérisés par une abondance et une diversité de clients moindre ainsi qu'une plus faible densité de nettoyeurs par rapport aux récifs « complexes ». Mes expériences démontrent que les nettoyeurs provenant d’environnements simples ne réussissent généralement pas à: 1) se nourrir contre leur préférence, 2) adapter leur comportement coopératif en présence d'un observateur et 3) offrir systématiquement la priorité à une source de nourriture temporaire plutôt qu’à une source de nourriture permanente. Ces résultats contrastent fortement avec les données publiées sur des comportements de recherche de nourriture dans des expériences en laboratoire traditionnelles. Pour mieux comprendre ces disparités, j'ai étudié dans le chapitre 3 si les deux groupes de nettoyeurs utilisent des indices différents lors de la prise de décisions au moment où ils vont se nourrir, particulièrement en ce qui concerne la priorité offerte aux clients. Les nettoyeurs provenant d'environnements socialement complexes sont capables de trouver un repère précis lors de la prise de décision, conduisant à une plus grande précision dans les tâches en laboratoire. Par contre, les nettoyeurs provenant d'environnements socialement simples utilisent une règle de base qui conduit à une performance plus faible lors de la même tâche.
Dans le chapitre 4, j'ai déterminé que les règles appliquées par les deux groupes de nettoyeurs en milieu naturel semblent être adaptées à leur habitat respectifs et que les contraintes cognitives des nettoyeurs de l'environnement socialement simple étaient spécifiques au contexte dans lequel ils vivent et dues au fait que la santé des nettoyeurs et leur performance cognitive dans un tâche abstraite ne diffèrent pas entre les deux groupes. Finalement, dans le chapitre 5, j'ai étudié la façon dont les nettoyeurs sont en mesure d'extraire des indices pertinents pour les décisions impliquant la tricherie et la recherche de refuge. J'ai démontré que la capacité des nettoyeurs à généraliser la reconnaissance de différentes espèces de prédateurs dans un contexte d'outil social. Cependant, cette capacité disparait lorsque les nettoyeurs sont testés dans un contexte abstrait.
Les résultats de cette thèse ont des retombées importantes pour faire avancer notre compréhension de la cognition chez les animaux et de la théorie des jeux évolutifs. Les résultats sont discutés en soulignant l’importance de l'approche écologique de la cognition et en suggérant des possibilités d’amélioration des modèles théoriques sur la question., Cooperation is defined as a ‘helping’ behaviour that provides direct fitness benefits to other individuals. Such behaviours have long intrigued biologists, as it poses a problem for classic evolutionary theory, i.e. why should an individual perform a behaviour that is beneficial to other individuals? Indeed, an expansive body of work on evolutionary game theory, as well as, empirical studies, have provided many mechanisms for promoting stable cooperation between unrelated individuals. Humans, however, often deviate from the optimal strategies predicted by theoretical models, which has emphasized the need to understand decision making processes. For example, the use of decision short cuts, known heuristics (or rules of thumb in non-human animals), allows individuals to make decisions quickly and accurately in frequently occurring situations, but may lead to less than optimal behaviour in novel contexts. Additionally, cognitive constraints, such as learning capabilities or failure to identify relevant environmental or social cues, may also cause deviations from predicated behaviour.
Using bluestreak ‘cleaner’ wrasse (Labroides dimidiatus) as a model system, the primary aims of this PhD thesis were 1) to investigate important mismatches between standard theoretical predictions regarding animal decisions during cooperative interactions and experimental data, as well as, 2) to explore how well cleaners are able to readily identify and use relevant cues for decision making. Cleaners engage in mutualistic relationships with so-called reef fish ‘clients’, which visit cleaner territories for ectoparasite removal. Cleaners, however, prefer feeding on nitrogen-rich client mucus, which constitutes cheating. Hence, to help ensure a cooperative cleaner, clients employ various partner control mechanisms, including punishment and partner switching. This dynamic cleaning mutualism has hitherto provided strong empirical evidence in support of evolutionary game theory for predicting cooperative behaviour.
In Chapter 2, however, I demonstrate that cleaners from socially complex reef environments largely outperform cleaners from socially simple reefs in classic cooperation- and cognition-based experiments. A lower abundance and diversity of reef fish clients, as well as, a lower density of cleaners, characterize socially simple reefs. Cleaners from these simple environments generally failed to: 1) feed against their preference, 2) adjust their cooperative behaviour in the presence of an audience, and 3) consistently provide service priority to a temporary food source over a permanent food source. These findings strongly contrast published evidence on cleaner foraging behaviour in laboratory-based experiments. To further understand these inconsistencies, in Chapter 3, I investigated whether the two cleaner groups used different cues when making foraging decisions; specifically, in regards to client service priority. Cleaners from the socially complex reef environment were found to use a precise cue when making decisions, leading to higher accuracy in the laboratory, whereas cleaners from the socially simple reef environment used a correlated cue, or a rule of thumb, which lead to an overall poorer performance.
In Chapter 4, I determined that the rules applied by the two cleaner groups in nature appear to be locally adaptive and that the cognitive constraints displayed by cleaners from the socially simple reef environment were context specific, as both cleaner body condition and cognitive performance in an abstract task did not differ between reef environments. Finally, in Chapter 5, I investigated how well cleaners are able to extract relevant cues for decisions involving cheating and refuge-seeking. Here, I demonstrated the ability of cleaners to generalize predator species in a social tool context; yet this ability disappeared when cleaners were tested in an abstract context.
Collectively, these results have important implications for both cognition and evolutionary game theory. The results are discussed with an emphasis placed on the importance of the ecological approach to cognition, as well as, suggestions for future modifications to theoretical models. - PublicationAccès libreWhat makes a cleaner a cleaner ?(2016)
; In his last presidential address to the Royal Society in 2005, Robert M. May stated that “The most important unanswered question in evolutionary biology, and more generally in the social sciences, is how cooperative behaviour evolved and can be maintained”. My thesis provides a contribution to answering this big question by investigating how one particular species evolved for an ecology that rests heavily upon cooperative interactions: the bluestreak cleaner wrasse Labroides dimidiatus. This species engages in up to 2000 cooperative interactions per day with dozens of other ‘client’ coral reef fishes, thus making it a prime system for studying cooperation between unrelated individuals. Conflicts between cleaners and clients arise because the former prefer to bite clients to eat their protective mucus rather than focusing on ectoparasites. In response to such exploitation, clients use various forms of partner control mechanisms that promote cooperative behaviour in cleaners. As a result, cleaners are known to use a diversity of strategic behaviours to determine when to cheat and when to cooperate. Cleaners’ behaviour thus appears very well adapted to the demands of their peculiar ecology.
In my thesis, I used a comparative approach to investigate which traits appear to be associated with the highly social ecology of cleaners, or in other words: What makes a cleaner a cleaner? Through a series of experiments, I compared the cognitive skills, escape performance, foraging ecology and vision of L. dimidiatus with other species of labrids that do not engage in cleaning (or only occasionally). These comparisons allowed me to identify some of the characteristics that set cleaners apart, and thus further our understanding of how social ecology can affect the evolution of a species.
In the first chapter, I showed that L. dimidiatus was able to fine-tune its level of cooperation to the specifics of different cleaning-related situations, an ability that was absent in the closely related Halichoeres melanurus. In the second chapter, I investigated whether the demands of a highly social lifestyle led to an overall increase of cognitive performance in L. dimidiatus, or whether performance was tightly linked to ecological demands. L. dimidiatus outperformed five other species of labrids in two ecologically relevant tasks. However, all species performed similarly in a task with little ecological relevance, suggesting that cognition in cleaners is tightly linked to the challenges faced in nature. In the third chapter, results from foraging experiments suggest that L. dimidiatus evolved a foraging position that allows for increased efficiency in cleaning interactions. In comparison with four other species, L. dimidiatus adopted a significantly lower body angle with regards to the substrate when foraging. Furthermore, this species experienced almost no reduction in efficiency when searching for cryptic food items in comparison with conspicuous ones, while the other species all performed worse in the cryptic condition. It thus appears that the peculiar foraging posture of L. dimidiatus is well suited for cleaning interactions. Unfortunately, my current data did not allow assessing whether the visual system also adapted for a low body angle while foraging. Finally, in the last chapter, I asked whether because of the service they provide to predators, a reduction in predation pressures led to the decay of escape performance in L. dimidiatus. Interestingly, measures of escape performance in a controlled laboratory setup showed that L. dimidiatus was among the top performers in comparison with 5 other labrids. These results suggest that the risks associated with cleaning interactions are sufficient to maintain a high escape performance in cleaners, despite their privileged relationship with predatory clients.
In summary, a wide range of characteristics appear to be important for cleaning interactions, and species that specialized in this activity seem to have undergone very different selective pressures than fishes with more standard ecologies. Identifying some of the key aspects related to the ecology of cleaners provides a good example of how the evolution of a species can be affected by the demands of a highly social life. In this system, I argue that competition among service providers and conflicts of interests between cleaners and clients appear to be the major drivers of adaptation. - PublicationAccès libreCooperation and deception: from evolution to mechanisms(2010)
- PublicationAccès libreDistinguishing four fundamental approaches to the evolution of helping(2008)
; The evolution and stability of helping behaviour has attracted great research efforts across disciplines. However, the field is also characterized by a great confusion over terminology and a number of disagreements, often between disciplines but also along taxonomic boundaries. In an attempt to clarify several issues, we identify four distinct research fields concerning the evolution of helping: (1) basic social evolution theory that studies helping within the framework of Hamilton’s inclusive fitness concept, i.e. direct and indirect benefits, (2) an ecological approach that identifies settings that promote life histories or interaction patterns that favour unconditional cooperative and altruistic behaviour, e.g. conditions that lead to interdependency or interactions among kin, (3) the game theoretic approach that identifies strategies that provide feedback and control mechanisms (protecting from cheaters) favouring cooperative behaviour (e.g. pseudo-reciprocity, reciprocity), and (4) the social scientists’ approach that particularly emphasizes the special cognitive requirements necessary for human cooperative strategies. The four fields differ with respect to the ‘mechanisms’ and the ‘conditions’ favouring helping they investigate. Other major differences concern a focus on either the life-time fitness consequences or the immediate payoff consequences of behaviour, and whether the behaviour of an individual or a whole interaction is considered. We suggest that distinguishing between these four separate fields and their complementary approaches will reduce misunderstandings, facilitating further integration of concepts within and across disciplines. - PublicationAccès libreVariation in Cleaner Wrasse Cooperation and Cognition: Influence of the Developmental Environment?
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