Ecomorphological correlates in ten species of subtropical seagrass fishes: diet and microhabitat utilization

Shape changes and growth trajectories in the early stages of three species of the genus Diplodus (Perciformes, Sparidae)

The larvae of three species of the genus Diplodus (Diplodus vulgaris, D. sargus, and D. puntazzo) colonize shallow waters along the Mediterranean coasts and, after a short period spent in the water column, they settle. For all three species this habitat transition is characterized by important shape changes mostly related to swimming capacity and feeding behavior. In this study, geometric morphometrics are used to characterize shape changes during the early juvenile life of specimens collected in a single locality in order to compare growth curves and allometric relationships. Size-related shape changes proved to be similar for all three species and are consistent with the ecological transition. A nonparametric smoothing technique (Loess) was used to fit the scatter of shape on size. The graphical representation (of most size-related shape variability) of this fitting technique shows how major shape changes are rapid for small sizes and slow down successively. The approach allows for the visualization of allometry and the fitting technique might help in defining the allometric growth pattern, thus contributing to the study of the autoecology of the species and in establishing terms for comparison with other ecologically or phylogenetically related species.

Visualizing allometry: Geometric morphometrics in the study of shape changes in the early stages of the two-banded sea bream, Diplodus vulgaris (Perciformes, Sparidae)

The sea bream, Diplodus vulgaris, is a marine teleost widely distributed in the Mediterranean and eastern Atlantic coastal waters. The larvae colonize shallow waters along rocky shores where, after a short period spent in the water column, they settle. Such habitat transition is characterized by important shape changes, mostly related to their swimming capacity and feeding behavior. In this study, geometric morphometrics has been used to characterize shape changes during early juvenile life. All specimens were collected in a single locality in the Gulf of Tigullio (Ligurian Sea), and data relative to their position in the water column and to the habitat selected were recorded. A total of 14 landmarks were collected on 82 specimens (range of standard length 11.2-82.8 mm). Landmark configurations were superimposed, and residuals were modeled with the thin-plate spline interpolating function: shape changes were visualized as splines. Growth trajectories were computed using relative warp analysis. Shape changes in the observed size range concern an overall broadening along the dorsoventral axis, a displacement of the mouth position, and a negative allometry of the head region. The growth trajectory resembles a theoretical saturating growth curve: shape change is fast for small sizes and slows down at standard lengths of approximately 28 mm, where an increase in size is not accompanied by a change in shape. This size value corresponds roughly to the size at which the settlement and the successive phase of dispersion of D. vulgaris have been observed in the area of study. This approach provides quantitative descriptors of shape changes and allows for the visualization of allometry. This method implies the definition of a new space for biological shapes in which shape trends and clusters can also be identified in relation to nonmorphological variables. As such it might contribute to the definition of the morphospace in the context of ecomorphology. J. Morphol. 237:137-146, 1998. © 1998 Wiley-Liss, Inc.