(1) 水圏における宿主―寄生関係を対象とした生態・分類・進化生物学的研究
(2) 河川性サケ魚類の生態学的研究

・Hasegawa R. Recent emergence and distributional expansion of the parasitic copepod Lernaeenicus cf. ramosus in Japanese waters revealed by web image surveys. Marine Ecology 47(2): e70086. 2026.
・Hasegawa R. & Poulin R. Colorful parasites: an overlooked frontier in animal coloration research. Trends in Parasitology 42(3): 162–172. 2026.
・Uemura Y., Hasegawa R., Taniguchi Y., Kawaguchi Y., Hasegawa K., Takeuchi Y., ... & Koizumi, I. (2026). Validating a past local extinction model using site‐level disappearances in a cold‐adapted salmonid under global warming. Freshwater Biology 71(5): e70234.
・Uemura Y., Otsuki Y., Hasegawa R., Naka M. & Koizumi, I. (2026). Mechanisms of local coexistence in juvenile congeneric salmonids in small tributaries with different thermal regimes. Oecologia 208(6): 70.
・Hasegawa R., Otsuki Y., Uemura Y., Furusawa C., Naka M., Kanno Y. & Koizumi I. Positive feedback between parasite infection and poor host body condition reduces host survival in the wild. Functional Ecology 39(3): 723–736. 2025.
・Hasegawa R. & Poulin R. Cause or consequence? Exploring authors’ interpretations of correlations between fish body condition and parasite infection. Journal of Fish Biology 107(2): 658–661. 2026.
・Hasegawa R. & Poulin R. Effect of parasite infections on fish body condition: a systematic review and meta-analysis. International Journal for Parasitology 55(8-9): 417–426. 2025.
・Hasegawa R. & Koizumi I. Do mouth-infecting parasites alter the foraging ecology of host fish? A test by parasitic copepod Salmincola markewitschi and white-spotted charr Salvelinus leucomaenis. Freshwater Biology 70 (1): e14362. 2025.
・Hasegawa R., Uemura Y., Yamashita Y., Inoshita M. & Koizumi I. Highly threatened status for the relict populations of ectoparasitic copepod Salmincola californiensis in Japan. Aquatic Conservation: Marine and Freshwater Ecosystems 35(2): e70073. 2025.
・Murakami L., ○Hasegawa R., Aruga N., Sato N., Nakamura S., Kajihara H. & Koizumi I. Mouth-attaching copepod Salmincola markewitschi reduces the body condition and growth of juvenile salmonid Salvelinus leucomaenis by decreasing host feeding activity: evidence from parasite removal experiment. Canadian Journal of Zoology 103: 1–8. 2025.
・Hasegawa R. & Koizumi I. Consistent negative correlations between parasite infection and host body condition across seasons suggest potential harmful impacts of Salmincola markewitschi on wild white-spotted charr Salvelinus leucomaenis. Zoological Science 41(2): 192–200. 2024.
Hasegawa R. & Koizumi I. Parasites either reduce or increase host vulnerability to fishing: a case study of a parasitic copepod and its salmonid host. The Science of Nature 110: 10. 2023.
・Hasegawa R., Katahira H. & Koizumi I. Salmincola markewitschi (Copepoda: Lernaeopodidae) or S. carpionis? A taxonomic confusion due to high morphological variations and a requirement for revising their taxonomic status. Folia Parasitologica 69: 025. 2022.
・Hasegawa R., Ayer C. G., Umatani Y., Miura K., Ukumura M., Katahira H. & Koizumi I. Potential negative effects and heterogeneous distribution of a parasitic copepod Salmincola edwardsii (Copepoda: Lernaeopodidae) on Southern Asian Dolly Varden Salvelinus curilus in Hokkaido, Japan. Parasitology International 87: 102529. 2022.
・Hasegawa R. & Koizumi I. Relative importance of host dependent vs. physical environmental characteristics affecting the distribution of an ectoparasitic copepod infecting the mouth cavity of stream salmonid. Ecological Research 36(6): 1015–1027. 2021.

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2019年　北海道大学水産学部海洋生物科学科　卒業
2021年　北海道大学環境科学院生物圏科学専攻修士課程　修了
2022年〜2024年　日本学術振興会特別研究員（DC2）
2024年　北海道大学環境科学院生物圏科学専攻博士後期課程　修了
2024年　Department of Zoology, University of Otago　日本学術振興会海外特別研究員
2026年　北海道大学北方生物圏フィールド科学センター臼尻水産実験所　助教

・2022年　日本生態学会　Best English Presentation Award
・2021年　日本寄生虫学会・衛生動物学会北日本支部会　若手奨励賞
・2021年　日本生態学会　最優秀ポスター発表賞
・2020年　個体群生態学会　最優秀ポスター賞
・2019年　日本生態学会北海道地区会　若手研究奨励賞

・IUCN Parasite Specialist Group Member

すべての生物には寄生虫がついていると言われるほど、寄生虫は普遍的な存在であり、その多様性は計り知れません。私は魚類をはじめとする水圏生物を対象に、宿主と寄生虫の相互作用や、寄生虫が生態系で果たす役割を調べています。多くの寄生虫では、その生態がほとんど解明されておらず、世界初となる発見がまだまだ身近にあります。研究活動を一緒に楽しみながら、新しい発見を世界へ発信していきましょう。