Cooperation: The path less travelled

Why do animals help raise offspring that aren’t their own? To answer this question, researchers from three countries joined forces to examine how cooperative breeding evolved in cichlid fish.

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A long trans-Atlantic flight, a connecting flight south for 10 hours, followed by a gruelling dusty, bumpy and extremely crowded 9-hour bus ride north. Why travel so far? To reach Lake Tanganyika of course. Few places on earth can match this lake’s biodiversity. Boasting the record as the world’s second deepest lake, Lake Tanganyika, together with its sister lakes Malawi and Victoria, is famous for hosting one of the most spectacular spectacles of species diversity. Dipping your head below the waters surface instantly reveals what an adaptive radiation looks like: hundred and hundreds of cichlid fish species of all shapes and sizes live in these tropical African waters.

For decades, researchers have traveled to the shores of these lakes, attracted by the mystery of why so many fish species exist here, why these species have arisen so quickly and why they display such an incredible variety of reproductive and social behaviours? Arguably among the most interesting and complex of all these behaviours is that of cooperative breeding, a breeding system in which a number of adults work together to defend and raise young. But determining why cichlids – and indeed any animal – cooperate remains one of the great challenges in evolutionary biology.

Sunset at our field site in Lake Tanganyika.

My interest in the cichlids began in the early 1990s and in 1997 I first visited Lake Tanganyika. My fascination for understanding cooperative behaviour, its origins, benefits and consequences has only grown over the years. To better understand cooperative behaviour my research group has focused on a group of cichlids from Lake Tanganyika called Lamprologines. What makes this group of about 80 fish species particularly interesting is that many of them are cooperative breeders, and these species represent the only fishes in the world to exhibit true cooperative breeding, the pinnacle of complex social behaviour. But not all Lamprologines are cooperative – in fact about two out of every three species are non-cooperative. Because these fishes are all close relatives that live in the same lake under similar ecological conditions, they provide a unique testbed for theories of how cooperation evolves.

Extensive debate remains about the role of kin selection versus ecological factors in driving cooperation. To address this issue, I was delighted to bring together a talented team of researchers from three countries, representing both then current and past members of my research group, the Aquatic Behavioural Ecology Laboratory.

Researchers from the Aquatic Behavioural Ecology Laboratory prepare for a dive on the shore of Lake Tanganyika.

My then postdoc, Dr. Constance O’Connor was excited to explore the implications of cooperation on sexual selection in these cichlids. She teamed up with my then PhD student, Cody Dey, an expert on phylogenetic path analyses. Together they joined forces with one of my first graduate students, Dr. John Fitzpatrick, now at the University of Stockholm and an expert on modern phylogenetic techniques. John quickly brought Dr. Susanne Shultz and Holly Wilkinson (who slogged away collecting oodles of life history details) from the University of Manchester on board and our team was complete.

By combining hard-won field collected data with detailed information from the literature we were finally able to examine the evolution of cooperative breeding in cichlids. Our approach diverged from previous comparative studies, as we simultaneously evaluating how kin selection and ecological factors promoted evolutionary transitions to complex cooperative societies. While previous studies found that transitions to cooperation among mammals, birds and hymenopterans were related to low levels of female promiscuity, in cichlids instead we found that living in groups, providing biparental care and eating a planktonic diet all strongly favored the evolution of cooperative breeding. It would appear that compared to other vertebrates, cichlid fishes took an alternative road to cooperation. Why these fascinating fishes took a different pathway remains our next research challenge.

Our paper in Nature Ecology & Evolution is here:

Sigal Balshine

Professor, McMaster University