Freshwater mussels across Europe exhibit physiological and behavioural adaptations to survive winter conditions. Climate change projections, including more frequent extreme weather events, are expected to intensify pressures on these ecosystems. In this study, we tested the temperature-size hypothesis, which posits that larger body size in ectothermic organisms is an adaptation to colder climates. We predicted that Anodonta anatina populations in northern regions would have larger shells than those in central and southern regions. Additionally, we hypothesised that harsher winters in northern regions require mussels to maintain higher glycogen levels as an energy reserve. We also explored whether shell size varies between lowland and upland populations, following the temperature-size rule, and whether supercooling (SCP) occurs primarily in northern populations as a complementary survival strategy. Northern populations had the highest glycogen levels, reflecting adaptations to colder conditions. SCP was rare (2.5%) and observed predominantly in northern mussels, suggesting limited reliance on freeze avoidance. Instead, it is likely that mussels employ mixed strategies, such as metabolic reduction and burrowing, to withstand winter. These findings link shell size, glycogen levels, and SCP to specific survival strategies, providing new insights into the cold tolerance mechanisms of freshwater mussels and their potential vulnerability to climate change.

• Keywords
• Anodonta anatina, Climate change, Frost resistance, Overwintering, Supercooling point, Survival strategies,
• MeSH
• Acclimatization * MeSH
• Ecosystem MeSH
• Adaptation, Physiological * MeSH
• Glycogen metabolism   MeSH
• Climate Change MeSH
• Bivalvia * physiology   MeSH
• Cold Temperature * MeSH
• Seasons MeSH
• Fresh Water MeSH
• Body Size MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Europe MeSH
• Names of Substances
• Glycogen MeSH

Facilitative and competitive interactions among coexisting parasite species, as well as among alternative host species, produce considerable ecological and evolutionary responses to host-parasite relationships. Such effects can be illuminated by impacts of non-native species on relationships in local communities. We used the association between parasitic European bitterling fish (Rhodeus amarus) and unionid mussels (which host bitterling eggs in their gills) to test the effects of the invasive Chinese pond mussel (Sinanodonta woodiana) and the presence of non-bitterling mussel macroparasites on the pattern of host mussel use by the bitterling across 12 unionid mussel communities with the absence or presence of S. woodiana (and variation in duration of coexistence with local species). While all six European mussel species were used by the bitterling (with the prevalence of > 30% in Unio spp.), no S. woodiana individual was infected by the bitterling. The presence of S. woodiana did not affect bitterling eggs distribution in native mussels. Large native mussels hosted more bitterling. Infection by non-bitterling parasites, mostly water mites (prevalence 47%) and trematodes (25%), did not affect rates of bitterling parasitism. We discuss our results in the context of the rapid evolution of non-native species in their new range and its implication on mussel conservation.

• Keywords
• Freshwater mussel, Host selection, Host-parasite interactions, Invasive species, Mussel parasitism, Parasite facilitation,
• MeSH
• Host-Parasite Interactions * MeSH
• Bivalvia * parasitology   physiology   MeSH
• Ovum * parasitology   MeSH
• Introduced Species * MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH