Ecomorphology and habitat utilization of Cottus species

We investigated relationships between morphological attributes and mesohabitat use in populations of Cottus carolinae. Field studies revealed significant differences between Ozark and prairie stream mesohabitats where populations of C. carolinae occurred. Features of the mesohabitat that were characteristic of each stream type correlated with intra- and inter-specific differences in morphological attributes of Cottus. The morphology of Cottus occurring in the deeper, slower, and siltier prairie stream exhibited larger head width and depth, body width and depth, and caudal peduncle width while those occurring in a shallower, faster flowing Ozark stream had longer pelvic fins, larger eyes, and deeper caudal peduncles. Each population had a morphology tailored to optimize its performance in a specific habitat. Results of laboratory based performance studies using a variable flow chamber revealed that critical current velocities (CCV) of live and preserved specimens were weakly associated with distinct combinations of morphological traits. Specimens with higher CCV measurements typically had longer pelvic fins, larger eyes, and deeper caudal fins (Ozark morphology). Those with lower CCVs had larger head width and depth, body width and depth, and caudal peduncle width (prairie morphology) in studies using cobble as the substrate. Differences in flow regimes between prairie and Ozark streams may generate specific niches for specific morphotypes, and current velocity may exert selective pressure on morphology.