Morphological plasticity allows organisms to adapt to varying environmental pressures and can be an important component of invasive species success. The rusty crayfish (Faxonius rusticus) is a prolific invader of North American lakes; however, its ability to expand through stream corridors may depend on its ability to tolerate hydraulic stresses. We utilized geometric morphometrics to examine shape variation in F. rusticus populations across three environments in Wisconsin and Michigan: lakes, low-velocity streams (<25 cm/s), and high-velocity streams (>40 cm/s) and then evaluate the ability of crayfish from different flow regimes to tolerate elevated water velocities in a recirculating flume.
Crayfish from high-velocity populations exhibited significantly more streamlined body forms and proportionally shorter, broader chelae compared to lentic populations. These adaptive traits likely reduce drag and facilitate effective flow deflection, allowing individuals to navigate high-velocity environments. When testing their ability to maintain position in the flume, we found that crayfish sourced from high-flow streams significantly higher velocities compared to those from low flow streams and lakes. Our results suggest that morphological plasticity and prior experience in flow may affect invasion of contrasting flow environments by optimizing both form and hydro-mechanical performance. These findings provide a framework for our current research into the plasticity and performance of F. rusticus and F. propinquus hybrids in Minnesota watersheds.