More than kinship, social isolation has a greater effect on toad tadpole behavior

Toad tadpoles, specifically the Japanese common toad (Bufo formosus), demonstrate social aggregation behavior, wherein they gather together to evade predators. This behavior is indicative of their association preferences, or inclination to recognize conspecifics. Certain toad tadpole species have exhibited sibling preference as well. The study of association preferences and kin recognition in tadpoles has become a significant aspect in the exploration of social behavior evolution.

Previous research has hinted at the possibility of microorganisms influencing communication via animal body odors, implying that pond water teeming with microbes might also impact social behavior. However, it remains uncertain whether such sociality is innate, shaped by early-life experiences, or influenced by the aquatic environment.

To address this uncertainty, Kazuko Hase from Kyoto University investigated the role of early-life social experiences and aquatic environment in shaping toad tadpole sociality. The findings were published in the journal Animal Cognition. Hase collected tadpoles from four separate egg masses around the University of Tokyo's Botanical Gardens, treating them as sibling groups.

After hatching, the tadpoles were raised under two different water environments—tap water and pond water—and two rearing conditions: group rearing with 20 siblings and solitary rearing. After two weeks, Hase conducted choice experiments where tadpoles were presented simultaneously with sibling and non-sibling individuals to evaluate their social preferences.

The results showed that the tadpoles did not exhibit a preference for siblings, regardless of rearing conditions, suggesting diminished kin recognition compared to other species. Hase observed that tadpoles reared in isolation exhibited a decreased tendency to approach other individuals, both siblings and non-siblings, and spent more time in neutral zones.

This indicates that the effects of social isolation persist across various aquatic environments. Notably, Hase did not observe any significant effects from the water environment.

Unlike closely related species where kin recognition has been confirmed during social aggregation, Hase was surprised to find that it was not essential for social aggregation in the Japanese common toad. This study suggests that the tadpole's social behavior is predominantly shaped by experiences with peers rather than kinship or the water environment, furthering our understanding of how some amphibians develop sociality.

The Japanese common toad is currently facing extinction, prompting Hase to emphasize the importance of protecting these threatened species. She also expressed delight at the contribution of her beloved toad tadpoles to scientific progress. Kazuko Hase, the corresponding author, concluded, "Social isolation, rather than kinship, influences association behavior in toad tadpoles (Bufo formosus)."