No evidence for general intelligence in a fish

Differences in inhibitory control in two species of Tanganyikan bower-building cichlids contrasting in building flexibility

A central challenge in understanding the evolution of cognition is the ability to compare a set of species differing in a trait of interest while being ecologically and phylogenetically close. Here, we examine whether differences in bower-building flexibility are related to differences in cognitive flexibility between two Tanganyikan cichlids. Cognitive flexibility enables animals to modify their decision rules when faced with new situations, and inhibitory control, the ability to inhibit a normally favoured response, is an essential component of this capacity. We tested male Aulonocranus dewindti and Cyathopharynx furcifer in a choice-against-preference paradigm. Both species clean their bowers of foreign objects and we found that both preferred to remove a snail shell over a stone. We tested their ability to modify this preference and learned to preferably select the stone instead of the shell. Although neither species showed clear learning of the new preference rule, both demonstrated inhibitory control through increased decision times and manipulations of the objects when selecting the stone. Specifically, A. dewindti, the species exhibiting greater behavioural flexibility in the construction of their bowers, selected the stone in fewer trials than C. furcifer, providing support for a link between behavioural flexibility in bower construction and cognitive flexibility.

Executive functions and brain morphology of male and female dominant and subordinate cichlid fish

BACKGROUND

Living in a social dominance hierarchy presents different benefits and challenges for dominant and subordinate males and females, which might in turn affect their cognitive needs. Despite the extensive research on social dominance in group-living species, there is still a knowledge gap regarding how social status impacts brain morphology and cognitive abilities.

METHODS

Here, we tested male and female dominants and subordinates of Neolamprologus pulcher, a social cichlid fish species with size-based hierarchy. We ran three executive cognitive function tests for cognitive flexibility (reversal learning test), self-control (detour test), and working memory (object permanence test), followed by brain and brain region size measurements.

RESULTS

Performance was not influenced by social status or sex. However, dominants exhibited a brain-body slope that was relatively steeper than that of subordinates. Furthermore, individual performance in reversal learning and detour tests correlated with brain morphology, with some trade-offs among major brain regions like telencephalon, cerebellum, and optic tectum.

CONCLUSION

As individuals' brain growth strategies varied depending on social status without affecting executive functions, the different associated challenges might yield a potential effect on social cognition instead. Overall, the findings highlight the importance of studying the individual and not just species to understand better how the individual's ecology might shape its brain and cognition.

Inhibitory control in teleost fish: a methodological and conceptual review

Inhibitory control (IC) plays a central role in behaviour control allowing an individual to resist external lures and internal predispositions. While IC has been consistently investigated in humans, other mammals, and birds, research has only recently begun to explore IC in other vertebrates. This review examines current literature on teleost fish, focusing on both methodological and conceptual aspects. I describe the main paradigms adopted to study IC in fish, identifying well-established tasks that fit various research applications and highlighting their advantages and limitations. In the conceptual analysis, I identify two well-developed lines of research with fish examining IC. The first line focuses on a comparative approach aimed to describe IC at the level of species and to understand the evolution of interspecific differences in relation to ecological specialisation, brain size, and factors affecting cognitive performance. Findings suggest several similarities between fish and previously studied vertebrates. The second line of research focuses on intraspecific variability of IC. Available results indicate substantial variation in fish IC related to sex, personality, genetic, age, and phenotypic plasticity, aligning with what is observed with other vertebrates. Overall, this review suggests that although data on teleosts are still scarce compared to mammals, the contribution of this group to IC research is already substantial and can further increase in various disciplines including comparative psychology, cognitive ecology, and neurosciences, and even in applied fields such as psychiatry research.

Cognitive flexibility in a Tanganyikan bower-building cichlid, Aulonocranus dewindti

Cognitive flexibility, the ability to modify one's decision rules to adapt to a new situation, has been extensively studied in many species. In fish, though, data on cognitive flexibility are scarce, especially in the wild. We studied a lekking species of cichlid fish in Lake Tanganyika, Aulonocranus dewindti. Males create sand bowers as spawning sites and maintain them by removing any objects falling into it. In the first part of our experiment, we investigated the existence of spontaneous decision rules for the maintenance of the bowers. We showed that if a snail shell and a stone are placed in their bower, fish prefer to remove the shell first. In the second phase of our experiment, we took advantage of this spontaneous decision rule to investigate whether this rule was flexible. We tested five individuals in a choice against preference task, in which the fish had to modify their preference rule and remove the stone first to be allowed to then remove the shell and have a clean bower. While there was no overall trend towards flexibility in this task, there was variation at an individual level. Some individuals increased their preference for removing the shell first, deciding quickly and with little exploration of the objects. Others were more successful at choosing against preference and showed behaviours suggesting self-regulatory inhibition abilities. Bower-building cichlids could therefore be a promising model to study cognitive flexibility, and other aspects of animal cognition in the wild.

Social learning in non-grouping animals

Social learning is widespread in the animal kingdom and is involved in behaviours from navigation and predator avoidance to mate choice and foraging. While social learning has been extensively studied in group-living species, this article presents a literature review demonstrating that social learning is also seen in a range of non-grouping animals, including arthropods, fishes and tetrapod groups, and in a variety of behavioural contexts. We should not be surprised by this pattern, since non-grouping animals are not necessarily non-social, and stand to benefit from attending to and responding to social information in the same ways that group-living species do. The article goes on to ask what non-grouping species can tell us about the evolution and development of social learning. First, while social learning may be based on the same cognitive processes as other kinds of learning, albeit with social stimuli, sensory organs and brain regions associated with detection and motivation to respond to social information may be under selection. Non-grouping species may provide useful comparison taxa in phylogenetic analyses investigating if and how the social environment drives selection on these input channels. Second, non-grouping species may be ideal candidates for exploring how ontogenetic experience of social cues shapes the development of social learning, allowing researchers to avoid some of the negative welfare implications associated with raising group-living animals under restricted social conditions. Finally, while non-grouping species may be capable of learning socially under experimental conditions, there is a need to consider how non-grouping restricts access to learning opportunities under natural conditions and whether this places a functional constraint on what non-grouping animals actually learn socially in the wild.

Fish can infer relations between colour cues in a non-social learning task

Transitive inference (TI) describes the ability to infer relationships between stimuli that have never been seen together before. Social cichlids can use TI in a social setting where observers assess dominance status after witnessing contests between different dyads of conspecifics. If cognitive processes are domain-general, animals should use abilities evolved in a social context also in a non-social context. Therefore, if TI is domain-general in fish, social fish should also be able to use TI in non-social tasks. Here we tested whether the cooperatively breeding cichlid Neolamprologus pulcher can infer transitive relationships between artificial stimuli in a non-social context. We used an associative learning paradigm where the fish received a food reward when correctly solving a colour discrimination task. Eleven of 12 subjects chose the predicted outcome for TI in the first test trial and five subjects performed with 100% accuracy in six successive test trials. We found no evidence that the fish solved the TI task by value transfer. Our findings show that fish also use TI in non-social tasks with artificial stimuli, thus generalizing past results reported in a social context and hinting toward a domain-general cognitive mechanism.