Lake Tanganyika: home of the only cooperatively breeding fishes in the world

Cooperation is an evolutionary paradox. It can enhance the survival of a species even though some individuals do not immediately benefit or reproduce. Cooperative breeding is a type of cooperation where a group works together to raise young. Cooperatively breeding groups often consist of two dominant breeders and several subordinate ‘helpers’. The dominant male and female generate offspring and the helpers assist in raising offspring and defending territories. This type of cooperation occurs in thousands of insects, hundreds of birds, and over one hundred mammals but the only known cooperatively breeding fishes are cichlids found in Lake Tanganyika, Africa (Reddon et al., 2017; Figure 1).

Figure 1: Lake Tanganyika in East Africa. Photo Credit: Wikimedia Commons

Lake Tanganyika is the second largest freshwater lake in the world by both depth and volume (Tierney et al., 2010). The African Great Lake hosts approximately 250 species of cichlid fishes, most of which cannot be found anywhere else in the world. Tanganyika’s cooperatively breeding fishes are all related and belong to the same family—the Lamprologine cichlids.

Within the Lamprologine family, there is considerable variation in social behaviour. While all cichlids provide parental care for their young, some of the Lamprologine cichlids live in cooperatively breeding groups (Figure 2A) and others live more solitary lifestyles (Figure 2B). Many of these cichlids establish and maintain territories regardless of their breeding system. Depending on the species, territories vary in size and can be found at different depth ranges and occupying different substrate. Defending territories can be much easier as part of a group since larger groups offer better protection from predators (Lima, 1995). However, cooperatively breeding cichlids live in strict, size-based dominance hierarchies so conflict within a group can be equally costly, especially for the smaller fish.

Figure 2. A. Neolamprologus pulcher, a cooperatively breeding Lamprologine cichlid. B. Telmatochromis temporalis, a non-cooperative Lamprologine cichlid. Photo Credit: Susan Marsh Rollo and Jen Reynolds.

Lake Tanganyika offers a valuable opportunity for scientists to study the evolution of cooperation because it contains cichlids that are genetically similar, yet some have evolved cooperative breeding behaviours (on five separate occasions!) and others have not (Dey et al., 2017). Biologists can compare cichlid species to understand how cooperative traits have evolved and feel confident that the evolution happened independently of environmental variables because the fish live in the same lake. Research on Tanganyikan cichlids has been ongoing for more than 30 years and even though we have learned an incredible amount in that time, these animals are still serving as valuable models to better understand the evolution of cooperation. This paradox has stumped scientists for so long that for Science Magazine’s 125th anniversary edition the editors identified the evolution of cooperation as one of the biggest questions in modern science.

Lake Tanganyika is undergoing immense change. Rapid population growth in the bordering regions and across East-Central Africa is synonymous with development, pollution and of course, fishing (Mölsä et al., 1999). Tanganyikan fishes are heavily relied upon as a protein rich food source by the surrounding countries. This means that it may become more challenging to study these unique fishes in their natural environment. Since many of these cichlids are commonly found in the aquarium trade, consumers can help negate the problem by providing their business to suppliers that discourage the continued overfishing of wild populations.

References

Dey, C.J., O’Connor, C.M., Wilkinson, H., Shultz, S., Balshine, S. and Fitzpatrick, J.L., 2017. Direct benefits and evolutionary transitions to complex societies. Nature ecology & evolution15, p.0137.

Lima, S.L. and Bednekoff, P.A., 1999. Back to the basics of antipredatory vigilance: can nonvigilant animals detect attack? Animal behaviour583, pp.537–543.

Mölsä, H., Reynolds, J.E., Coenen, E.J. and Lindqvist, O.V., 1999. Fisheries research towards resource management on Lake Tanganyika. Hydrobiologia407, pp.1–24.

Reddon, A.R., O’Connor, C.M., Nesjan, E., Cameron, J., Hellmann, J.K., Ligocki, I.Y., Marsh-Rollo, S.E., Hamilton, I.M., Wylie, D.R., Hurd, P.L. and Balshine, S., 2017. Isotocin neuronal phenotypes differ among social systems in cichlid fishes. Royal Society open science4, p.170350.

Tierney, J.E., Mayes, M.T., Meyer, N., Johnson, C., Swarzenski, P.W., Cohen, A.S. and Russell, J.M., 2010. Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500. Nature Geoscience3, pp.422–425

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