When observing tadpoles (frog larvae) swimming in groups in a pond, larvae of different sizes may be swimming together.Previous studies have shown that amphibian larvae tend to flock with relatives using odor, but no studies have considered differences in body size (developmental stage) at the same time.

　Flocking has the benefit of reducing the risk of being attacked by predators, but it also creates competition such as competition for food, making large opponents a threat to small individuals.It is not desirable for competition between relatives to occur, so some sizes may prefer to flock to unrelated individuals.Based on this idea, we conducted an experiment using larvae of Rana japonica to simultaneously verify the difference in kinship and size in the preference of the group partner.

　Test individuals to be observed were placed in a water tank, and two stimulating individuals of different sizes (large or small) or related (blood-related or unrelated) were placed on the left and right.An experiment was conducted in which the residence time of each of the left and right stimulating individuals was calculated and compared, while changing the pattern of the combination of the stimulating individuals.

　As a result, small test individuals tended to prefer smaller stimuli to larger stimuli, regardless of kinship.On the other hand, the larger test individuals preferred smaller stimulators over larger stimuli only if both stimulators were unrelated.This result was not seen when the small stimulator was a relative, and was considered to be a property to reduce competition for food among relatives.

　This is the world's first report of a developmental change in preference that considers both the size of the partner and the blood relationship at the same time, as in this discovery, and further research is needed in the future.

Paper information:[Animal Behavior] Developmental effects on behavioral response for social preferences in frog tadpoles, Rana ornative ntris