Zebra Mussels are freshwater bivalves, native to Eurasia, that have become invasive pests in North American waters. First detected in Lake Saint Clair, Michigan in 1988, they quickly spread to all the Great Lakes and across the continent. Zebra Mussels multiply rapidly and attach to surfaces, fouling the hulls of boats and water intakes. Zebra Mussels will attach to native bivalves to their detriment. Even aquatic arthropods are not immune from Zebra Mussel attachment.
Dragonfly larvae are aquatic and feed while burrowing into the aquatic soils at the bottom of bodies of water. Dragonfly larvae that do not completely bury themselves can become a site of attachment for Zebra Mussels. The mussels are shed with the cuticle during molting. However, an attached mussel may prevent a dragonfly larva from completely burying to escape notice of predators. Thus, Zebra Mussels are decreasing the populations of some dragonfly species by increasing predation. Large last instar dragonfly larvae may support multiple zebra mussels. The additional weight may prevent the dragonfly larva from climbing out of the water to molt into an adult. This is an additional mortality factor.
A recent study in the Journal of Insect Behavior measured colonization rates of Zebra Mussels and found that 91 percent of Macromia illinoiensis dragonfly larvae had at least one Zebra Mussel attached. The dragonfly larvae that were the fastest at burying in the sand at the bottom were the least likely to be colonized.
When a new species first invades a new habitat, many of the species will be poorly adapted. The least well adapted individuals will be lost and the population will shift toward individuals that are more resistant to the invader. In this case, those dragonfly larvae that are slow to bury will be the most vulnerable. “Slow burying” individuals and their “slow burying” genes will be eliminated. Individuals with faster burying times and their “fast burying genes” will increase in frequency in the population as those individuals are least affected by the Zebra Mussels.
Invasive species are doing incredible harm to our ecosystems and causing economic damage. It is important to support and improve programs and institutions that are needed to prevent the movement of these invaders.
Dragonfly larvae (Hagenius brevistylus) with attached Zebra Mussels
Photo: Shannon McCauley
http://labs.eeb.utoronto.ca/rowe/McCauley.htm
