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First published online April 18, 2006
Journal of Experimental Biology 209, 1678-1689 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02139

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Size, strength and allometry of joints in the articulated coralline Calliarthron

Patrick T. Martone

Hopkins Marine Station of Stanford University, Pacific Grove, CA 93950, USA

View larger version (20K): [in a new window]   Fig. 1. Diagram of a representative frond from Calliarthron cheilosporioides.

View larger version (25K): [in a new window]   Fig. 2. Mechanical tests used to measure the strength of genicula and intergenicula. (A) Three-point bending test. Fronds were compressed between three razor blades until intergenicula snapped. (B) Pull-to-break test. Fronds were stretched until genicula broke. The asterisks indicate approximate break locations.

View larger version (18K): [in a new window]   Fig. 3. Diagram of a Calliarthron frond after it has been broken. (A) Broken genicula were numbered according to their original position in the frond. Data from each broken geniculum was paired with the planform area of the frond that it would have supported in flow (e.g. encircled segments would be paired with geniculum no. 24). (B) Transverse view of a broken frond segment.

View larger version (15K): [in a new window]   Fig. 4. Cross-sectional areas of genicula (circles) and intergenicula (triangles) from C. tuberculosum (black symbols) and C. cheilosporioides (white symbols) from the large size class as functions of geniculum position. Lines represent linear regressions fitted to each data set. ANCOVA; for F and P values, see text.

View larger version (17K): [in a new window]   Fig. 5. Comparison of mean cross-sectional areas (A, mean ± s.d.) of genicula from small fronds (white circles) and large fronds (black circles). Central error bars were omitted to clarify the graph. The numbers of genicular measurements are given in parentheses. NS, not significantly different; *P<0.05, **P<0.01.

View larger version (15K): [in a new window]   Fig. 6. Breaking forces of genicula from large fronds (black circles; N=107) and small fronds (white circles; N=50) as functions of their cross-sectional areas. For regression equations, see text.

View larger version (22K): [in a new window]   Fig. 7. Comparison of the mean breaking stress (; mean ± s.e.m.) of large and small Calliarthron fronds.

View larger version (18K): [in a new window]   Fig. 8. Data collected from broken genicula in two representative fronds. (A) Breaking forces, (B) cross-sectional areas and (C) breaking stresses of genicula as functions of the planform areas of distal frond segments supported in flow. (D) Diagram of a representative frond oriented as in A–C.

View larger version (12K): [in a new window]   Fig. 9. (A) Breaking forces of genicula from three representative fronds as functions of the planform areas of distal frond segments supported in flow. (B) Diagram of hypothetical Calliarthron frond, explaining the pattern of decreasing slope with increasing frond size. 1x, 2x and 4x refer to the number of new growth units distal to genicula in the specified regions. See text for details.

View larger version (17K): [in a new window]   Fig. 10. Risk factor indices (Ir) of genicula from the large size class as a function of the planform areas of distal frond segments supported in flow.