Can members of the Gila complex be identified as morphologically distinct across life history stages?

Authors: Clinton J. Moran, Carlos Lerma, Yordano Jimenez, Alice C. Gibb

Year: 2012 (xliv)

Abstract

Cyprinids in the genus Gila from the southwestern United States are difficult to identify by species because members of the genus, especially at juvenile and young adult life history stages, have very similar body designs. Species identification within the genus is further complicated by hybridization between coexisting species and putative morphological differences within a species between drainages. This study sought to quantify the differences between species in the genus as well as possible differences within a species between waterways using standard meristic traits and measurements of body proportions taken from digital images of preserved specimens and live specimens collected in the field. Because fishes at later life history stages are more distinct from one another we focused on characteristics that can distinguish species at juvenile and young adult stages. We note that morphological differences are minimal in juvenile fish, but changes in proportion arise as fish grow larger. Some morphological characteristics varied between water ways and among Gila species including: caudal peduncle depth, caudal peduncle length and dorsal fin base length. Although morphological differences did exist within a species, it is not clear if this variability is genetic, or the result of developmental plasticity. These results could have further implications in reexamining the species distinctions within the genus Gila as well as assisting with field identifications. Further investigation will be conducted on various species in the Gila complex to determine the functional significance of morphological variation within a species.