Division of labour in social insects

Division of labour in social insects

IISc study of Indian paper wasp demonstrates who becomes the queen and who takes up other works

Using an Indian paper wasp, researchers at Benguluru’s Indian Institute of Science (IISc) have for the first time been able to witness in laboratory settings the minimum conditions required for the emergence of cooperation and division of labour — important for evolutionary success and ecological dominance — among social insects. How the two important features influence productivity (total brood of the colony) was already known theoretically but not adequately demonstrated empirically till now.

Using newborn virgin female wasps (Ropalidia marginata) the researchers demonstrated the spontaneous emergence of cooperation and two types of division of labour — reproductive and non-reproductive. The reproductive division of labour determines who becomes the queen and reproduces, and who becomes the worker and carries out tasks other than reproduction. When more than two workers are present in a nest, an additional division of labour emerges that determines who does the housekeeping job and who does work outside the nest.

The team led by Prof. Raghavendra Gadagkar from the Centre for Ecological Sciences at IISc studied social wasps maintained in the laboratory as solitary, pairs and triplets. “Even virgin wasps can lay eggs. Since male wasps never involve in nest-related work we used only female wasps for the study,” says Souvik Mandal from IISc’s Centre for Ecological Sciences and coauthor of a paper published in the journal Proceedings of the National Academy of Sciences.

While there was no possibility of emergence of either cooperation or division of labour when there was only one wasp, cooperation and reproductive division of labour came about when two or more wasps were present. The non-reproductive division of labour among workers emerged only when three wasps were present.

Physical aggression

Physical aggression such as biting, pecking, nibbling and chasing helps in determining the dominant and subordinate distinction among the individuals. “There was no difference in body size or age of the aggressor but the fighting abilities were different,” says Anindita Brahma from the Centre for Ecological Sciences at IISc and first author of the paper.

In the case of pairs, the dominant individual became the queen and the subordinate became the worker. With triplets, the most dominant becomes the queen, and the most dominant wasp among the workers built the nest, did the housekeeping and feeds the larvae while the least aggressive wasp fetched food, water, and building material for the nest. “There is increased productivity when three wasps are present as both reproductive and non-reproductive division of labour come into play besides cooperation,” says Brahma.

Increasing productivity

Cooperation and reproductive division of labour as seen in pairs are inadequate for increasing productivity. “Compared with pairs, triplets are able to produce more offspring… they have more productivity,” says Prof. Gadagkar. “Even with three individuals we could see the difference in productivity. If there are more than three then productivity will keep on increasing, we think.”

“Because we isolated the wasps in the laboratory, we were able to determine the minimum conditions needed for the emergence of cooperation and division of labour,” says Prof. Gadagkar. “For cooperation to emerge just two individuals are sufficient. The worker wasp does not sulk or both don’t build their own nests. Instead, the worker helps the queen to build the nest, feed the brood and maintain the nest — that’s cooperation.”

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