Seasonal Dynamics of Sex Ratio, Reproduction, and Parasite-specific Feminization in the Hermit Crab Pagurus filholi at a Fixed Coastal Site in Chiba, Japan
Reproductive output in intertidal crustaceans is shaped by seasonal changes in host demography and their interaction with parasitic castration. However, parasite-species-resolved time series remain limited, particularly for hermit crabs. Through monthly monitoring of a Pagurus filholi population over one year, we revealed pronounced seasonal variation in host sex ratio, female reproductive activity, and the prevalence of two co-occurring rhizocephalans, Peltogasterella gracilis and Peltogaster postica. Although both parasites showed marked prevalence peaks in early summer, they differed in host-sex bias and in their effects on male secondary sexual characters. In particular, P. gracilis was strongly associated with the development of the female-specific second pleopod in males. Our parasite-resolved time series therefore provides a robust baseline demonstrating parasite-specific differences in phenology, sex bias, and infection-associated feminization.
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