Testing local adaptations of affiliate freshwater pearl mussel, Margaritifera laevis, to its host fish, Oncorhynchus masou masou

• Published in: Ecological research Vol. 36; no. 5; pp. 803 - 814
• Main Authors: Kitaichi, Hitoshi, Negishi, Junjiro N., Ito, Daisetsu, Miura, Kazuki, Urabe, Hirokazu
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.09.2021; Blackwell Publishing Ltd
• Subjects: Acclimation; Acclimatization; Adaptation; Allopatry; Cysts; Encystment; endangered species; Fish; Fish reproduction; Freshwater; Freshwater fish; Freshwater molluscs; Gills; Glochidia; Habitats; Heterogeneity; host‐parasite; Hypotheses; immunity; infection; Infections; Inland water environment; Larvae; Limiting factors; Margaritifera laevis; Metamorphosis; Mollusks; Mussels; Oncorhynchus masou; Oncorhynchus masou masou; Parasites; Salmon; Sympatric populations; Tanks
• ISSN: 0912-3814; 1440-1703
• DOI: 10.1111/1440-1703.12245

Understanding the limiting factors of the reproduction process in host–affiliate relationships is a high priority. We examined the effects of habitat location on the reproductive process of freshwater pearl mussels Margaritifera laevis (Bivalvia, Unionida) as a parasite using sympatric and allopatric Oncorhynchus masou masou (Actinopterygii, Salmoniformes) as a host fish. Initial infection rates of parasitic larvae (glochidia) and transformation rates to cysts (encysted glochidia) were examined for all parasite‐host combinations from three habitat locations (a total of nine combinations) to test the hypothesis that sympatric pairs of mussels and fish result in the highest success rates of glochidia infection and encystment. Measurements of glochidia‐infected fish reared in flow‐through experimental indoor tanks were taken at the initial infection point as well as at encystment, 2 weeks after the infection. Results disagreed with our hypothesis. Instead, an unexpected heterogeneity in a pathological deformity in gills explained a greater amount of variance in these processes. This deformity was responsible for reducing the initial infection rate and increasing the metamorphosis rates of initially attached glochidia to cysts. The field‐measured prevalence of the gill deformity was low in all habitat locations, indicating that the deformity occurred during the acclimation period before infection for relatively small‐sized host fish more susceptible to infection. Our results did not show the local adaptation of parasitic freshwater mussels to host fish but shed light on one of the least studied factors, providing an empirical underpinning of the importance of pathologically diversified host conditions in the reproductive processes of unionid mussels. Initial infection rates of parasitic larvae (glochidia) and transformation rates to cysts (encysted glochidia) were examined for all parasite‐host combinations from three habitat locations in flow‐through experimental indoor tanks. Our results did not show the local adaptation of parasitic freshwater mussels to host fish, but an unexpected heterogeneity in a pathological deformity in gills explained a greater amount of variance in these processes