Use of geometric morphometrics to differentiate Gila (Cyprinidae) within the upper Colorado River basin

Video images of 215 adult Gila robusta and 148 endangered Gila cypha were c ollected from May 1991-October 1992 at eight Colorado River basin localitie s (seven upper basins and one lower basin), The two species were sympatric at five of these locations; G. robusta was absent at one site, whereas G. c ypha was missing at two others, Saggital views of each individual were vide otaped and 25 morphological points (15 anatomical landmarks and 10 helping points) identified. Bookstein shape coordinates were calculated from Cartes ian coordinates of these landmarks and points, whereas centroid size was us ed as a measure of body size. Shape differences were evaluated among popula tions of each species using MANOVA and canonical variates analysis. In G. c ypha, variation encompassed three aspects: nuchal hump (most pronounced in Grand Canyon forms), relative head size (larger in Cataract Canyon forms), and caudal peduncle dimensions (shorter with a tapering depth in Cataract C anyon forms but longer and uniformly deeper in those from Desolation Canyon ), Nuchal development in G. robusta is slight, hence only head and peduncle dimensions distinguished populations, Those individuals from Cataract Cany on had relatively shorter peduncles that (again) tapered in depth from ante rior to posterior, whereas G. robusta from Desolation Canyon possessed pedu ncles that were much longer and of uniform depth. Specimens from Debeque an d Rifle Canyons had proportionally smaller heads. Variation among all 13 po pulations (i.e., both species together) was evaluated using relative warp a nalysis, with G. cypha and G. robusta clearly separated at all sympatric lo cations except those from Desolation and Caratact Canyons, Here, body shape s of the two species converged. Overall, shape variation in both species is clinal, Although results from our geometric morphometric analysis were sta tistically similar to those based on distances derived from a truss analysi s, the geometric approach visually demonstrated phenotypic differences amon g populations and species and this, in turn, has management implications.