Effects of Allometry, Sex, and River Location on Morphological Variation of Freshwater Drum Aplodinotus grunniens in the Wabash River, USA
Morphology frequently varies with phylogeny, body size, sex, and phenotypic plasticity. However, the relative influence of these variables is unknown for most taxa. Morphological variation of Freshwater Drum Aplodinotus grunniens in the Wabash River, USA was described using geometric morphometrics. A MANCOVA model of shape indicated that morphological variation was primarily influenced by allometry (body size), sex, and river location. Among all individuals, at least 50% of the variability in morphology was a product of body size while sex and river km (collection locale) accounted for 10% and 5% of the overall variability in shape, respectively. However, when mature and immature individuals were analyzed separately, mature individuals demonstrated no morphological signal concurrent with river km, while at least 45% of the variability in immature shape was attributed to river locale. The contributions of allometry, sex, and river gradient on Freshwater Drum morphology suggest that morphological variation is largely a result of a combination of developmental, sexual, and environmental influences.
Map of continuous Wabash River collection reach area. River km notations indicate upstream and downstream limits of collection area.
Location of Freshwater Drum morphology landmarks. Landmarks correspond to anterior snout (1), superior margin of head (2), anterior spinous dorsal origin (3), posterior spinous dorsal origin (4), anterior rayous dorsal origin (5), superior posterior caudal peduncle (6), inferior posterior caudal peduncle (7), posterior medial caudal fin edge (8), anterior anal-fin origin (9), anterior pelvic-fin origin (10), ventral opercular isthmus (11), superior pectoral-fin origin (12), and anterior medial edge of orbital socket (13).
Thin plate spline deformation grids relative to consensus image for three morphological axes. See text for details. RW1 depicted an ontogenic gradient that covaried positively with body size. RW2 depicted an ontogenic gradient that covaried positively with body size and an inverse river km gradient only in immatures. RW3 depicted an ontogenic gradient that covaried positively relative to body size and a positive river km gradient in immatures.
Scatterplot of RWA1 and total length (mm) with regressions for mature male and female and immature individuals. Closed circles indicate females, open circles indicate males, and open squares indicate immature individuals. Solid line indicates female mean shape, light dotted line indicates male mean shape, and heavy (thick) dotted line indicates immature mean shape. Higher RWA1 scores indicate increased robustness. See text and Figure 3 for details and deformation gradients.
Scatterplot of RWA2 and total length (mm) with regressions for mature male and female and immature individuals. Closed circles indicate females, open circles indicate males, and open squares indicate immature individuals. Solid line indicates female mean shape, light dotted line indicates male mean shape, and heavy (thick) dotted line indicates immature mean shape. Lower RWA2 scores indicate increased robustness in immatures. See text and Figure 3 for details and deformation gradients.
Scatterplot of RWA2 and river km with regressions for mature male and female and immature individuals. Closed circles indicate females, open circles indicate males, and open squares indicate immature individuals. Solid line indicates female mean shape, light dotted line indicates male mean shape, and heavy (thick) dotted line indicates immature mean shape. Lower RWA2 scores indicate increased robustness in immature morphologies of upstream reaches. See text and Figure 3 for details and deformation gradients.
Scatterplot of RWA3 and total length (mm) with regression line for combined male, female, and immature individuals. Closed circles indicate females, open circles indicate males, and open squares indicate immature individuals. Solid line indicates female mean shape, light dotted line indicates male mean shape, and heavy (thick) dotted line indicates immature mean shape. Higher RWA3 scores indicate reduced snout and caudal region and robustness. See text and Figure 3 for details and deformation gradients.
Scatterplot of RWA3 and river km with regressions for mature male and female and immature individuals. Closed circles indicate females, open circles indicate males, and open squares indicate immature individuals. Solid line indicates female mean shape, light dotted line indicates male mean shape, and heavy (thick) dotted line indicates immature mean shape. Higher RWA3 scores indicate increased robust immature morphologies in upstream reaches. See text and Figure 3 for details and deformation gradients.
Consensus images of mature male, female, and immature individuals from discriminant function analysis.
Contributor Notes
Associate Editor: T. Grande.