Evaluating interspecific competition effects on morphological variation of Orconectes rusticus

Abstract

Morphological variation in response to environmental conditions is widespread among macroinvertebrates and can affect ecology and evolution in organisms. Interspecific competition may affect morphological variation of plastic traits that can confer a competitive advantage. Invasion of the rusty crayfish, Orconectes rusticus, in the Monocacy River provides the opportunity to test the hypothesis that interspecific competition affects morphological variation. Two populations of O. rusticus were examined at two separate sites, one site dominated by O. rusticus, and the other site where O. rusticus and O. virilis were present. Crayfish were photographed, and the body and chelae were analyzed with geometric morphometrics. Male O. rusticus had significantly larger carapace length, abdominal and chelae width, and different body shape when in competition with O. virilis. Shape in female crayfish was significantly different between sites, but metrics of size (carapace length, abdomen width, and chelae width) were not significantly different. These results suggest that interspecific competition in crayfish species plays a role in influencing morphological variation within river ecosystems.