title: Why does Gila elegans have a bony tail? A study of swimming morphology convergence.
abstract: Caudal-fin-based swimming is the primary form of locomotion in most fishes. As a result, many species have developed specializations to enhance performance during steady swimming. Specializations that enable high swimming speeds to be maintained for long periods of time include: a streamlined body, high-aspect-ratio (winglike) caudal fin, a shallow caudal peduncle, and high proportions of slow-twitch ("red") axial muscle. We described the locomotor specializations of a fish species native to the Colorado River and compared those specializations to other fish species from this habitat, as well as to a high-performance marine swimmer. The focal species for this study was the bonytail (Gila elegans), which has a distinct morphology when compared with closely related species from the Southwestern United States. Comparative species used in this study were the roundtail chub (Gila robusta), a closely related species from low-flow habitats; the common carp (Cyprinus carpio), an invasive cyprinid also found in low-flow habitats; and the chub mackerel (Scomber japonicus), a model high-performance swimmer from the marine environment. The bonytail had a shallow caudal peduncle and a high-aspect-ratio tail that were similar to those of the chub mackerel. The bonytail also had a more streamlined body than the roundtail chub and the common carp, although not as streamlined as the chub mackerel. The chub mackerel had a significantly higher proportion of red muscle than the other three species, which did not differ from one another. Taken together, the streamlined body, narrow caudal peduncle, and high-aspect-ratio tail of the bonytail suggest that this species has responded to the selection pressures of the historically fast-flowing Colorado River, where flooding events and base flows may have required native species to produce and sustain very high swimming speeds to prevent being washed downstream.
authors.affiliation: Biological Sciences, Northern Arizona University, 617 S. Beaver St., Flagstaff, AZ 86011, USA. Electronic address: cmoran@fairfield.edu.
authors.forename: Clinton J
authors.initials: CJ
authors.lastname: Moran
authors.affiliation: School of Mathematical and Natural Sciences, Arizona State University, 4701 W. Thunderbird Rd., Glendale, AZ 85306, USA.
authors.forename: Lara A
authors.initials: LA
authors.lastname: Ferry
authors.affiliation: Biological Sciences, Northern Arizona University, 617 S. Beaver St., Flagstaff, AZ 86011, USA.
authors.forename: Alice C
authors.initials: AC
authors.lastname: Gibb
mesh_terms: D000818:Animals; D003530:Cyprinidae / Q000033:anatomy & histology* / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology; D013550:Swimming / Q000502:physiology*; D013623:Tail / Q000033:anatomy & histology*
keywords: Caudal fin; Cyprinidae; Gila complex; Peduncle; Vertebral column