A study done by researchers at Karlstad University shows that the parasitic larva of freshwater mussels can manipulate their host fish into swimming further upriver to habitats well-suited for when their adult selves.
“The greater upstream movement of infested host fish, particularly at the time of excystment, is the clearest indication of an extended phenotype [host manipulation] expressed by glochidia [parasitic larvae of freshwater mussels]”, says Sebastian Rock at Karlstad University.
If you’ve ever watched The Last of Us, you’re been shown an extreme view of a parasite ridden world, however, the history, biology and ecology of parasites is more complicated than just a bug that replaces your tongue or that one roommate that never does the dishes and always steals your cereal in the morning. Like it or not, almost 40% of all species ever describes are parasites in one way or another.
While some parasites cause serious diseases in their hosts, others cause very little harm to their hosts, freshwater mussels are one such example. As adult mussels don’t move around too much, they need a way to get from place to place, their larvae grab a hold of fish and hitchhike a ride to some new place. Unfortunately, not all parts of a river are created equal, and some are better suited to be a home to an adult mussel than others, and some researchers at Karlstad University show just that. Not only do fish infected with larval mussels move further upriver, but they chose sections of the river that are ideal for the mussels once they become adults and fall of the fish.
The study on host manipulation by freshwater mussels was published online in the journal of Behavioural Ecology on May 4th, 2025. The authors are Sebastian L. Rock, P. Anders Nilsson, Johan Watz, Olle Calles and Martin Österling, researchers at both Karlstad and Lund universities.
- Read the full published article here: https://doi.org/10.1093/beheco/araf043
