LIFE HISTORY OF QUADRULA NODULATA: WHICH HOST SPECIES OF FISH DOES IT DEPEND ON?

Derek J. Ochi, Macalester College
Jessica N. Ramirez, Macalester College
Daniel J. Hornbach, Macalester College
Mark C. Hove, Macalester College

Freshwater mussels are one of the most imperiled groups of animals in North America, with 43% of taxa now extinct, endangered, or threatened. Their benthic life history makes the group particularly vulnerable to human activities. Larval metamorphosis occurs on the gills of a host fish. Conservation efforts could be improved by identifying life history needs of Quadrula nodulata.

To better understand the life history of Quadrula nodulata we collected glochidia from several gravid females of this species from the Mississippi River and compared them with glochidia from gravid females of Actinonaias ligamentina, Lampsilis higginsii, and Quadrula pustulosa from both the St. Croix and Mississippi Rivers (Q. nodulata is not found in the St. Croix). We used these glochidia to conduct host suitability trials using standard methods. Glochidia and juvenile mussels from our host trials as well as juveniles released by naturally infested fishes were measured using scanning electron microscopy. Discriminant analysis using hinge/length ratio, height/length ratio and length alone, allowed us to do a reasonable job of classifying glochidia into species. Evidence suggests that the juvenile from the channel catfish is a Quadrula species, most likely Quadrula pustulosa (71.8%) or Quadrula nodulata (28.2%). However, the naturally infested catfish was caught at Spring Lake, Mississippi River near the mouth of the St. Croix River during early summer. Channel catfish move about in the spring followed by a more sedentary lifestyle in the summer. If the data set is restricted to glochidia from the Mississippi, where the channel catfish was caught, then it is Quadrula nodulata, as valve height values for the two species do not overlap in this river. We plan to use molecular analysis to assist us with juvenile mussel identification in these difficult situations.