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First published online September 9, 2005
Journal of Experimental Biology 208, 3493-3502 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01808

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Adaptive bone formation in acellular vertebrae of sea bass (Dicentrarchus labrax L.)

Sander Kranenbarg^1,*, Tim van Cleynenbreugel², Henk Schipper¹ and Johan van Leeuwen¹

¹ Experimental Zoology Group, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands
² Division of Biomechanics and Engineering Design, K.U. Leuven, Celestijnenlaan 200A, 3001 Leuven, Belgium

View larger version (20K): [in a new window]   Fig. 1. Phylogeny of the major taxa of Actinopterygii (based on Nelson, 1994). A representative example of each group is shown for each taxon. The colour of each fish indicates the percentage of species having cellular bone (red) or acellular bone (green). This figure is based on data from over 500 species. Data is taken mainly from Kölliker (1859) and Moss (1961, 1965), with some additional data from Meunier (1989), Meunier and Huysseune (1992) and Sire et al. (1990). Numbers next to each taxon indicate counted number of species with cellular bone (red) and acellular bone (green).

View larger version (36K): [in a new window]   Fig. 2. (A) Example of lordotic vertebral column (red) represented as a column with eccentricity. (B) Column with eccentricity, e, under compression with force, F. (C) Part of the column representing a vertebra from the region with eccentricity, e (lordotic region), illustrating the compressive force, F, and the induced bending moment, M. The broken white line represents the neutral axis, and y represents the distance from the neutral axis.

View larger version (15K): [in a new window]   Fig. 3. Graphical presentation of the dimensionless stress versus the dimensionless position . The blue line represents the loading of a typical normal vertebra, and the red line represents the loading of a typical lordotic vertebra. The open circles illustrate the loading in a situation with zero eccentricity (pure compression).

View larger version (34K): [in a new window]   Fig. 4. Pairwise comparison of three situations, viz. normal vertebrae with normal eccentricity (normal, blue), normal vertebrae with doubled eccentricity (double, grey) and lordotic vertebrae with their characteristic high eccentricity (lordotic, red) (see top row). Box plot comparison of mean between (A) normal vertebrae and normal vertebrae with double eccentricity, (C) normal and lordotic vertebrae and (E) lordotic and normal vertebrae with double eccentricity. As the volumes of all finite elements in the models are approximately equal, the mean dimensionless strain energy density, , is approximately equal to the total dimensionless strain energy in each vertebra. Subplots B, D and F show a histogram of the percentage of the total number of elements in a number of categories. Comparisons are equal to those in subplots A, C and E, respectively. The last category includes all elements with >2000. Standard deviation is indicated by boxes around the solid line. Colour of the boxes indicates the loading situation. Grey shading indicates significant (P<0.05 in a one-tailed non-parametric Wilcoxon test) differences between the respective groups.

View larger version (74K): [in a new window]   Fig. 5. Distribution of over the vertebral centra (rostral is to the left). (A-C) Vertebrae of the 35 mm TL stage; (D-F) vertebrae of the 45 mm TL stage. The first column (A and D) shows normal vertebrae, the second column (B and E) shows normal vertebrae with double eccentricity and the third column (C and F) shows lordotic vertebrae, as illustrated by the top row. White arrows in D indicate parasagittal ridges. Abbreviations: ha, haemal arch; na neural arch.

View larger version (42K): [in a new window]   Fig. 6. (A) Spatial distribution of bone volume (in mm3) during development along the rostral-caudal axis of lordotic vertebral centra (red) in comparison with normal vertebral centra (blue). `Position on centrum' indicates position (in percentage of centrum length) along the rostral-caudal axis of the vertebral centrum. `Total length' indicates total length of the specimens and thus developmental stage. Blue and red solid lines indicate the actual vertebrae (normal and lordotic, respectively) measured. (B) Difference of mean bone volume between lordotic and normal vertebrae as a function of position along the vertebral centrum. Dark green indicates the region where the 95% confidence intervals of lordotic and normal vertebrae do not overlap.

View larger version (95K): [in a new window]   Fig. 7. Parasagittal sections through a normal vertebra (A) and a lordotic vertebra (B), stained according to Crossmon (Romeis, 1968). (C) An enlargement of the yellow box in B. Acellular bone of the vertebral centrum is blue (A). Abbreviations: cb, chondroid bone; ft, fibrous tissue; mt, muscle tissue; nc, notochord; ns, neural spine; nt, neural tube. The asterisk indicates the position of the intervertebral ligament. Scale bar is 200 µm in A and B and 50 µm in C.