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Fish cooperate for selfish reasons

Stockholm University

In an article published yesterday in the journal Nature Ecology and Evolution John Fitzpatrick, a lecturer at Stockholm University, and his colleagues show self interest is what leads to the evolution of complex cooperative societies in African cichlid fishes.

"In some group living animals - like meerkats - a few dominant individuals do all the breeding and receive help in raising their offspring from other members of the group. In birds and mammals, this helping behaviour evolves because the helpers are related to the offspring they are caring for. This wasn't the case in cichlid fishes", says Fitzpatrick, the senior author on the study.

To determine which behaviours are associated with cooperatively rearing offspring, the researchers examined the behaviours of almost 70 cichlid species living in Lake Tanganyika, Africa.

"Our results show that cichlids followed a different path to cooperation that what we see in other animal groups", explained Sigal Balshine, a Professor at the McMaster University and one of the authors of the article. "For cichlids, living in a group reduces your chances of being eaten by a predator. So it is likely that fear of predators is a driving factor behind the evolution of helping behaviour".

"From an evolutionary standpoint, this is highly interesting", says John Fitzpatrick. "These cichlid fish have found a model where cooperation works because of it is so hard to make it on your own. Basically, it´s cooperation for selfish reasons."

Cooperation in cichlid fish may be different form other species because they have short life spans, which prevents family groups from becoming established.

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The study Direct benefits and evolutionary transitions to complex societies is an important piece in our knowledge of the evolutionary development of complex societies. It´s available here: http://www.nature.com/articles/s41559-017-0137

For more information contact John Fitzpatrick at the Department of Zoology on +46 73 710 63 59. Email john.fitzpatrick@zoologi.su.se.

Direct benefits and evolutionary transitions to complex societies

The selective forces driving the evolution of cooperation are intensely debated. Evolutionary transitions to cooperative breeding, a complex form of cooperation, are hypothesized to be linked to low degrees of promiscuity, which increases intragroup relatedness and the indirect (i.e. kin selected) benefits of helping. However, ecological factors also promote cooperative breeding, and may be more important than relatedness in some contexts. Identifying the key evolutionary drivers of cooperative breeding therefore requires an integrated assessment of these hypotheses. Here, using a phylogenetic framework that explicitly evaluates mating behaviours and ecological factors, we show that evolutionary transitions to cooperative breeding in cichlid fishes were not associated with social monogamy. Instead, group living, bi-parental care and diet type directly favoured the evolution of cooperative breeding. Our results suggest that cichlid fishes exhibit an alternative path to the evolution of complex societies compared to other previously studied vertebrates, and these transitions are driven primarily by direct fitness benefits.

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