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

Abstract

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.

Ontogenetic development of the sagittal otolith of the anchovy, <em>Anchoa tricolor</em>, in a subtropical estuary

“…In the early 2000s, the emergence of the geometric morphometrics applied to fishes brought a new precise and accurate tool to bioecology, fisheries research and related areas (Loy et al 1998, Torres et al 2000. Ponton (2006) stated its use in otolithology and its reference has quickly become a classical citation.…”

The pace of morphological change: historical transformation of skull shape in St Bernard dogs

“…Loy et al 1998;Monteiro 1999). The amount of variation for which the regression model accounted was quantified as a percentage of the total shape variation, computed using the Procrustes metric (Goodall 1991;Klingenberg & McIntyre 1998).…”

Larval development and shape variation of the kelpfish <em>Myxodes viridis</em> (Teleostei: Clinidae)

“…Procrustes ANOVA was carried out to assess the relative amounts of variation among individuals and of measurement error using MorphoJ. In general, allometric changes between somatic parameters are expressed by a potential equation (see Lleonart et al 2000); however, in geometric morphometry, allometry is widely characterized by multivariate regression of shape on size (usually centroid size or log-transformed centroid size); such regressions often fit the data well and the allometric shape changes tend to affect the entire structures under study (Loy et al 1998, Mitteroecker et al 2004, Klingenberg and Marugán-Lobón 2013. Therefore, a regression between a regression score of each independent variable (Procrustes coordinates) and centroid size was carried out with MorphoJ (Sidlaukas et al 2011).…”