Abiotic factors, like temperature, can have a profound effect on the establishment success of invasive species. Interpreting and predicting these effects can be difficult in the context of co-invading hosts and parasites. In the Upper Mississippi River region (UMRR), the invasive faucet snail (Bithynia tentaculata) and its trematode parasites have been contributing to major die-offs of waterfowl, the trematodes’ definitive host with over 135,000 birds having succumbed to trematodiasis since 2002. As the snails continue to disperse southward down the river, anticipated overlay with high density migration stopover sites presents the potential for significant increases in waterfowl mortality. In our study, we aimed to understand the fitness consequences of extreme temperature exposure on snails and their parasites. We predicted that 1) parasitized snails will be more susceptible to extreme temperatures and will have higher mortality rates than uninfected snails, and 2) juvenile snails will be more susceptible to extreme temperatures, regardless of infection status, than adults. Adult snails collected in the UMRR and naïve lab-reared juvenile snails were subjected to warming protocols intended to mimic the temperature extremes of the Mississippi River. Activity levels were assessed and mortality was tracked. Adult snails were examined for metacercarial parasite presence post-mortem.
Results/Conclusions
First stage experiments have indicated that adult snails in the increased temperature treatment did not experience a significantly higher mortality rate than control snails (p =0.095), and metacercarial presence did not influence mortality in either treatment. The infected adult snails had low mean infection intensity by metacercariae in both treatments. Metacercariae are non-feeding and may not have a strong effect on snail energy resources when infection is low or moderate. Though our first prediction was not supported, there was strong evidence to support our second prediction. Juvenile snails exposed to high temperature treatments had a significantly higher mortality rate than control juveniles (p < 0.001). If juvenile snails are susceptible to higher temperatures, survival rate of new clutches in the southern parts of the river will be low. It will be difficult for snails to establish populations further south, thereby lessening the perceived risk to migrating waterfowl.