Studying the evolution of social behaviour in one of Darwin\u2019s Dreamponds: a case for the Lamprologine shell-dwelling cichlids

Etienne Lein,Alex Jordan

doi:10.1007/s10750-020-04473-x

Abstract

The link between the evolution of advanced sociality and cognition has been an important concept across fields and taxonomic boundaries. However, in many study systems, ecological and phylogenetic confounds impair evolutionary inferences drawn when comparing social organization. Here, we highlight the value of the shell-dwelling Lamprologine cichlids of Lake Tanganyika in studies of cognitive and social evolution. These species show differences in social organization, both within and across species, but otherwise exhibit remarkable similarities in their ecology and life history. We focus on the ecological and social attributes of 15 Lamprologine cichlids that live in permanent association with empty gastropod shells, often in syntopy and with largely overlapping ecological niches. We then discuss difficulties with terminology and categorization of social organization, outlining current and emerging methodologies to address these limitations. Our goal is twofold: (i) to gather available empirical evidence on the behaviour, life history, and ecology of shell-dwelling Lamprologine cichlids, highlighting their potential in comparative studies of cognition and evolution, and (ii) to stimulate debate and critical appraisal of current terminology and categorizations of social structure, ideally leading to more precise and empirically standardized definitions of sociality in cichlids.

Highlights

Social interactions are ubiquitous in the animal world, from territorial behaviour in otherwise solitary animals, to brief mating unions, through to permanent social bonds; the consequences of social interactions are complex and far reaching
We argue that Tanganyikan shell-dwelling cichlids represent a unique system for assessing the effect of the social environment on brain/cognitive evolution
Used classifications of sociality or social complexity, fall short of capturing a relevant metric of the cognitive demands related to the social environment of individuals within differing groups, populations, or species

Summary

Introduction

Social interactions are ubiquitous in the animal world, from territorial behaviour in otherwise solitary animals, to brief mating unions, through to permanent social bonds; the consequences of social interactions are complex and far reaching. The shell-dwelling cichlids are a species group that possess many valuable attributes in studies of social evolution and behaviour: (i) at 15-23 species, a powerful comparative sample (Table 1), (ii) with close and wellresolved phylogenetic relationships, (iii) and similar body sizes; similar ecological factors, including (iv) overlapping dietary niches with similar feeding modalities, and (v) sympatric patterns of distribution, or even syntopic mosaic communities with similar risk environments on the macro-habitat level, and (vi) a low variation in environmental complexity, due to their resembling, permanent, association with empty snail shells; (as a result of this shell-dwelling lifestyle, it is conceivable that other life-history traits, including brood size or age at sexual maturity, are similar across these cichlid species) Despite these remarkable similarities, the shell-dwelling Lamprologine cichlids are highly divergent with regard to their social structure. The ability to produce aquarium hybrids, and to potentially observe such hybrids in the wild (Koblmuller et al, 2007) makes it conceivable to establish and study ‘‘intermediate’’ social phenotypes in this study system, which would eventually allow for an even more nuanced analysis of social complexity

Conclusion

Compliance with ethical standards