Abstract
Cooperative breeding is a social system where offspring receive care not only from their parents but also from other group members. The life history traits related to the evolutionary transition towards such complex systems are still poorly understood. This study investigated the evolutionary transition from non-cooperative to cooperative breeding in lamprologine cichlid fishes endemic to Lake Tanganyika using phylogenetic comparative methods. Ancestral state reconstruction revealed that the evolutionary transition from non-cooperative to cooperative breeding occurred at least seven times independently. Comparative analyses using life history data obtained from field observations and from published literature revealed an evolutionary link between cooperative breeding and clutch and body size, but not egg size: cooperative breeders were smaller and laid fewer eggs than non-cooperative breeders. These findings suggest an evolutionary scenario where cooperative breeding evolved in smaller species, most likely because of ecological factors, such as an increased predation risk, driving the evolution of complex social systems. This was followed by a reduction in clutch size. These results shed light on the role of ecological settings in life history trait evolution and how they mediate the transition towards a complex social organization.
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The data and R script for analysis that support the findings of this study are available in Dryad (https://doi.org/10.5061/dryad.d51c5b0f9)71.
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Acknowledgements
The members of the Maneno Tanganyika Research Team, Laboratory of Animal Sociology of the Osaka Metropolitan University, Kutsukake Research Group of the Graduate University for Advanced Studies, and Animal Ecology Laboratory of the Kyoto University provided helpful comments and discussion. This study was financially supported by KAKENHI (nos. 19K23765, 20J01170, 21K06346, 23KK0131, and 25K02309 to S.S., 20J13379 to T.S., 19H03306 and 20K20630 to M.K., and 20KK0168 and 23H03868 to S.A.) and Swiss National Science Foundation (nos. 31003A_166470 and 310030_185021 to J.F.). This paper was improved by the comments and suggestions made by the four anonymous reviewers and editors of Communications Biology. We remember the late Dr. Hirokazu Tanaka, who started this project.
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Experimental design: S.S., S.O., T.I., M.K., and S.A. Field observation and sampling: S.S., T.S., M.M., F.T., M.H., R.H., R.I, Y.Y., and S.A. Egg and morphological measurement: S.S., T.I., S.A., and M.H. Statistical analysis: S.S., S.O., T.I., M.M., and S.A. Support of statistical analysis: N.K. Writing of the manuscript: S.S., S.O.T.I., J.G.F., M.M., N.K., and S.A.
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Satoh, S., Okuno, S., Ito, T. et al. Repeated evolution of cooperative breeding and life history traits in Lake Tanganyika cichlids. Commun Biol (2026). https://doi.org/10.1038/s42003-026-09814-5
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DOI: https://doi.org/10.1038/s42003-026-09814-5
