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. (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
Murakami, L., Hasegawa, R., Aruga, N., Sato, N., Nakamura, S., Kajihara, H., & Koizumi, I. (2025). Mouth-attaching copepod Salmincola markewitschi reduces the body condition and growth of juvenile salmonids, Salvelinus leucomaenis, by decreasing host feeding activity: Evidence from parasite removal experiment. Canadian Journal of Zoology, 103, 1-8. doi: 10.1139/cjz-2024-0158 Journal - Research Article
Hasegawa, R., Poulin, R., & Salloum, P. M. (2025). Testing for consistency in co-occurrence patterns among bacterial taxa across the microbiomes of four different trematode parasites. Microbial Ecology, 88, 45. doi: 10.1007/s00248-025-02545-w Journal - Research Article
Hasegawa, R., & Poulin, R. (2025). Effect of parasite infections on fish body condition: A systematic review and meta-analysis. International Journal for Parasitology. Advance online publication. doi: 10.1016/j.ijpara.2025.03.002 Journal - Research Article