PhD Environmental Science, Hokkaido University (Japan), 2024
MSc Environmental Science, Hokkaido University (Japan), 2021
BSc Fisheries, Hokkaido University (Japan), 2019
Email: ryotahase344922@gmail.com
Evolutionary and Ecological Parasitology Research Group
Research interests
- Ecology and Taxonomy of parasitic copepods
- Ecology of freshwater fish (mainly salmonids)
- Association between fish body condition and parasite infections
- Parasite community assembly
I’m a parasite ecologist mainly working on host-parasite relationships between salmonid fishes and parasitic copepods of the genus Salmincola, which infects the mouth and gill cavities of their hosts. My focus has been on how copepod infections alter host behaviour, body condition, and survival. Then, my interest shifted to parasite-parasite interactions within individual hosts and their consequences on host ecology. Here in Dunedin, I’m currently working on whether priority effects contribute to creating trematode communities in amphipod hosts and their consequences for host fitness and ecosystem functioning.
Current postdoctoral project
Priority effects in parasite community assembly and its consequences on amphipod host fitness and ecosystem functioning
(JSPS Overseas Research Fellow; Japanese Society of Proportion of Science)
Publications
Hasegawa, R., de Angeli Dutra, D., Presswell, B., Bennett, J., McDougall, C., Buschang, K. E., Chai, X., & Poulin, R. (2026). Does bigger mean sicker? A systematic review and meta-analysis of the intraspecific relationship between host body size and parasite infection across vertebrate taxa. Oikos. Advance online publication. doi: 10.1002/oik.11823 Journal - Research Article
Hasegawa, R., Walter, C. B., & Poulin, R. (2026). Do parasite effects on fish body condition depend on host size and external temperature? A meta-analytic approach. Journal of Zoology. Advance online publication. doi: 10.1111/jzo.70148 Journal - Research Article
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. doi: 10.1007/s00442-026-05905-6 Journal - Research Article
Hasegawa, R. (2026). 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. doi: 10.1111/maec.70086 Journal - Research Article
Hasegawa, R., & Poulin, R. (2026). Colorful parasites: An overlooked frontier in animal coloration research. Trends in Parasitology, 42(3), 162-172. doi: 10.1016/j.pt.2026.01.004 Journal - Research Other