The tadpoles that don't care about their siblings

Researcher

Overview

Kyoto, Japan -- Amphibian larvae -- often known as tadpoles -- exhibit a behavior known as social aggregation, where they gather together as a way to avoid predators. These interactions are evidence of their association preferences, or their tendency to recognize members of their own species. Some varieties of tadpoles have even shown a preference for their siblings.

These association preferences and kin recognition in tadpoles have become a key topic in understanding the evolution of social behavior. Recent studies have suggested that microorganisms may be influencing communication through animal body odors, indicating the possibility that pond water rich in microbes may also affect social behavior. Yet whether this sociality is innate, shaped by early life experiences, or the aquatic environment, has remained unclear.

This uncertainty motivated Kazuko Hase at Kyoto University to investigate how early-life social experiences and the aquatic environment influence the development of sociality.

Hase collected tadpoles of the species Bufo formosus, the Japanese common toad, from four different egg masses found around the University of Tokyo's Botanical Gardens, treating the egg masses as sibling groups. After hatching, she raised the tadpoles using an experimental design combining two different water environments -- tap water and pond water -- with two different rearing conditions -- group rearing with 20 siblings, and solitary rearing.

After two weeks, Hase conducted choice experiments that involved simultaneously presenting the tadpoles with both sibling and non-sibling individuals in order to assess their social preferences. She established sibling, non-sibling, and neutral zones within the experimental tanks and tracked the tadpoles' movements for 60 minutes, analyzing the amount of time spent in each zone.

The analysis revealed that the tadpoles did not exhibit any preference for siblings, regardless of rearing conditions, indicating lower kin recognition than the tadpoles of other species. Hase did observe that the tadpoles reared in isolation showed a reduced tendency to approach other individuals, whether sibling or non-sibling, and spend more time in the neutral zones, suggesting that the effects of social isolation remain robust across aquatic environments. She did not observe any significant effects resulting from the water environment.

"Unlike closely related species in which kin recognition has been confirmed during social aggregation, I was surprised to find that it is not essential for social aggregation in the Japanese common toad," says Hase, who is the corresponding author.

This study indicates that the social behavior of this tadpole is shaped more by experiences with peers than by kinship or water environment, contributing to a better understanding of how some amphibians develop sociality.

"The Japanese common toad is facing the threat of extinction, so we want to help protect them," says Hase. "I am also delighted that these toad tadpoles that I love so much are contributing to scientific progress."

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Related link

Reference article about the endangered status of the Japanese common toad: 
The Toad Crisis in Tokyo: What Urban Communities Can Do — AmphiBios