The role of adaptive resistance in a widespread freshwater mussel species

Abstract

Abstract Organism features, such as size, weight, sex and age, among others, can influence the success of parasitism. For species that depend on a host to complete their life cycle, such as freshwater mussels (Bivalvia, Unionida), understanding how these traits influence parasitism can help guide management actions aimed at improving their reproductive success, ultimately benefitting their conservation. In this study, the physiological compatibility between the duck mussel Anodonta anatina and its host fish was investigated in a simultaneous infestation experiment on four (three native and one non‐native) fish species using sympatric and allopatric host strains. The success of glochidia metamorphosis in juvenile mussels was evaluated as a function of host species, strain and fish length. Successful metamorphosis was achieved in almost all fish species tested and differences were detected between allopatric and sympatric strains, with higher values found in allopatric hosts. Allopatric strains of primary hosts produce more juveniles than marginal hosts and non‐native species. In addition, larger fish have lower rates of metamorphosis. The results confirm recent findings showing high variation in the metamorphosis success of A. anatina glochidia among different native and non‐native hosts, both in the natural environment and in artificial laboratory infestations. Allopatric hosts were more suitable for encystment, demonstrating potential adaptive immunity, not yet observed in A. anatina. Nevertheless, A. anatina may temporarily exploit the naivety of smaller fish regardless of strain. Overall, the results suggest that mussel propagation, reproduction and reintroduction efforts should consider the mechanisms that influence adaptive immunity in fish, including differences in compatibility within and between populations of sympatric and allopatric host strains. This situation should be taken into account, as successful metamorphosis is an important factor in the selection of hosts for juvenile development, especially in efforts to propagate endangered mussel species.