This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In some group-living animals, individuals other than the parents help care for offspring. This breeding system, known as cooperative breeding, is thought to have evolved from monogamous family groups in which offspring remain in their natal group and engage in various cooperative behaviors, including helping to care for younger siblings.
Cooperative breeding has been documented in mammals and birds. Among fishes, it is known in approximately 30 species of cichlids inhabiting Lake Tanganyika in East Africa. In these species, helpers engage in a variety of cooperative behaviors, including egg care, nest maintenance, and territorial defense.
However, it remains unclear whether cooperative breeding occurs in fishes outside the family Cichlidae. In this study, researchers investigated Betta brownorum, a freshwater fish native to Southeast Asia, under captive conditions. B. brownorum has previously been suggested to exhibit cooperative breeding based on anecdotal observations that nonparental individuals attack heterospecific intruders entering their territory.
However, this idea has not been quantitatively tested, and the extent of cooperation in this species remains unclear. The research is published in the journal Behavioral Ecology and Sociobiology. The researchers conducted detailed observations of B. brownorum in captivity.
In intrusion experiments, they introduced an individual of another species into the territories of B. brownorum family groups. They found that both breeding adults (parents) and subordinate individuals (retained offspring) frequently attacked the intruders, indicating that subordinate individuals contribute to territorial defense. During these experiments, they also observed one instance in which a subordinate individual remained at the bubble nest while the breeding male was absent.
To further investigate the role of subordinate individuals, the researchers conducted experiments in which they were temporarily removed from their family groups. Attacks on heterospecific intruders by breeding adults increased during subordinate removal and decreased after the subordinates were returned to their family groups. These results suggest that subordinate individuals reduce the burden of territorial defense on breeding adults.
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