Sexual Dimorphism and Size-Related Changes in Body Shape in Tule Perch (Family: Embiotocidae), a Native California Live-Bearing Fish
The Tule Perch, Hysterocarpus traskii, is a viviparous and externally monomorphic, internally fertilizing fish. Despite appearing monomorphic, males and females are expected to differ in body shape because the different reproductive roles occupied by the sexes should influence patterns of selection and, ultimately, lead to differences in morphology. The objectives of this study were to determine if the Sacramento–San Joaquin subspecies of Tule Perch (H. t. traskii) exhibit (1) sexual dimorphism in body shape, (2) size-related changes in body shape, and (3) sexual size dimorphism. Geometric morphometric analyses indicated that H. t. traskii exhibited significant sexual dimorphism of body shape and identified the mid-body and caudal peduncle regions as the most effective discriminators between the sexes. Females were narrower through the caudal peduncle and mid-body and had anal-fin origins that were more posteriorly located than males. Additionally, H. t. traskii exhibited significant size-related changes in body shape. Larger fish were deeper bodied with blunter snouts and wider caudal peduncles. The eyes of larger fish were relatively smaller and located higher on the body than those of smaller fish. Hysterocarpus t. traskii did not exhibit differences between the sexes in standard length, but males were significantly heavier than females.
(A) Landmarks used for geometric morphometric shape analysis of H. t. traskii: (1) anterior tip of snout, (2) most anterior point of eye outline, (3) most posterior point of eye outline, (4) dorsal origin of the operculum, (5) posterior boundary of the supraoccipital bone, (6) dorsal-fin origin, (7) soft dorsal origin, (8) dorsal-fin insertion, (9) dorsal insertion of caudal fin, (10) lateral line at caudal fin, (11) ventral insertion of caudal fin, (12) anal-fin insertion, (13) anal-fin origin, (14) pelvic-fin insertion, (15) pelvic-fin origin, (16) pectoral-fin insertion, (17) pectoral-fin origin, and (18) ventral origin of the operculum. (B) Generalized Procrustes Analysis (GPA) of 130 male (blue) and 139 female (pink) H. t. traskii. GPA mathematically removes non-shape variation due to size, scale, and position.
Canonical Variates Analysis of the sexes. Results demonstrate that one dominant canonical variate axis described significant differences between male (blue circles) and female (pink squares) H. t. traskii.
Deformation grid of the first canonical variate (CV1). This deformation grid depicts the shape transformation associated with the CV1 axis, which represents the variables that maximally discriminate between the sexes. Circles on the grid represent the reference body shape for male H. t. traskii and the vectors demonstrate the direction and relative magnitude of local shape change to the reference body shape of female H. t. traskii.
Deformation grids of regression of H. t. traskii. These deformation grids depict the shape transformation associated with the regression of shape on centroid size for female (A) and male (B) H. t. traskii. Circles on the grid represent the reference body shape for smaller H. t. traskii and the vectors demonstrate the direction and relative magnitude of local shape change to the reference body shape of larger H. t. traskii.
Contributor Notes
Associate Editor: D. Buth.