VISUALIZING ALLOMETRY - GEOMETRIC MORPHOMETRICS IN THE STUDY OF SHAPECHANGES IN THE EARLY STAGES OF THE 2-BANDED SEA BREAM, DIPLODUS-VULGARIS (PERCIFORMES, SPARIDAE)

The sea bream, Diplodus vulgaris, is a marine teleost widely distribut ed in the Mediterranean and eastern Atlantic coastal waters. The larva e colonize shallow waters along rocky shores where, after a short peri od spent in the water column, they settle. Such habitat transition is characterized by important shape changes, mostly related to their swim ming capacity and feeding behavior. In this study, geometric morphomet rics has been used to characterize shape changes during early juvenile life. All specimens were collected in a single locality in the Gulf o f 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 w ere modeled with the thin-plate spline interpolating function: shape c hanges were visualized as splines. Growth trajectories were computed u sing relative warp analysis. Shape changes in-the observed size range concern an overall broadening along the dorsoventral axis, a displacem ent of the mouth position, and a negative allometry of the head region . The growth trajectory resembles a theoretical saturating growth curv e: shape change is fast for small sizes and slows down at standard len gths of approximately 28 mm, where an increase in size is not accompan ied by a change in shape. This size value corresponds roughly to the s ize at which the settlement and the successive phase of dispersion of D. vulgaris have been observed in the area of study. This approach pro vides quantitative descriptors of shape changes and allows for the vis ualization of allometry. This method implies the definition of a new s pace for biological shapes in which shape trends and clusters can also be identified in relation to nonmorphological variables. As such it m ight contribute to the definition of the morphospace in the context of ecomorphology. J. Morphol. 237:137-146, 1998. (C) 1998 Wiley-Liss, In c.