Highly toxic seeds of the Japanese star anise Illicium anisatum are dispersed by a seed-caching bird and a rodent


Many field studies on plant seed dispersal teach us that we cannot judge the effective dispersal mode of plants by examining only the morphologies of the fruits and seeds. In the present study, we explored the seed dispersal process of an evergreen tree, the Japanese star anise Illicium anisatum, which is highly toxic, containing neurotoxins in both the fruits and seeds. The fruits exhibit ballochory, a mode of seed dispersal characterized by explosive fruit dehiscence, and the extreme toxicity apparently seems to deter fruit and seed consumption by animals. However, we found that the dispersal distance afforded by this mode was very short (≤ 6 m). In the field, we confirmed that a passerine species, the varied tit Poecile varius, was the only consumer of the seed in foliage, and the bird actively transported seeds or fruits to either cache or consume them. Seeds setting on the forest understory were removed by the small Japanese field mouse Apodemus argenteus, and were also dispersed by this animal. Analysis of seedling spatial distribution revealed that seedlings were highly aggregated near standing trees or fallen logs, suggesting that caching facilitated seed dispersal. This study warns that plant toxicity and the ecological function thereof should not be evaluated based only on limited knowledge of the effects on humans and mammals. Our results pose further questions on the evolution of toxin tolerance in seed-caching animals and on the mutualism between toxic plants and animals.

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We are grateful to Yuji Suda, the members of the Animal Ecology Laboratory at Rikkyo University, and those of the Community Dynamic Laboratory of the Forestry and Forest Products Research Institute for their assistance and constructive comments on our study. We thank Naoko Sashimura for informing us of the study site, Kaoru Niiyama for his help in identifying tree seedlings, and Shoji Naoe for allowing us to use his monitoring devices. We thank James Worth for checking English writing. We are grateful to the Izu Forest Management Office of the Forest Agency of Japan for permission to work in a national forest. During the study, the first author was partly supported by a Research Fellowship from the Japan Society for the Promotion of Science for Young Scientists (; Grant number 2610007) and the second author was supported funding by JSPS KAKENHI (Grant number JP17H00797).

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Correspondence to Tetsuro Yoshikawa.

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ESM 1 Footage of a varied tit Poecile varius handling the fruit of the Japanese star anise Illicium anisatum and then transporting a seed and a fruit. (MP4 24321 kb)

ESM 1 Footage of a varied tit Poecile varius handling the fruit of the Japanese star anise Illicium anisatum and then transporting a seed and a fruit. (MP4 24321 kb)

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Yoshikawa, T., Masaki, T., Motooka, M. et al. Highly toxic seeds of the Japanese star anise Illicium anisatum are dispersed by a seed-caching bird and a rodent. Ecol Res 33, 495–504 (2018).

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  • Ballochory
  • Secondary metabolites
  • Plant defense
  • Toxicity