Rosenberg. G. D. & Hughes, W. W. 1991 01 15: A metabolic model for the determination of shell composition in the bivalve mollusc, Mytilus edulis. Lethaia, Vol. 24. pp. 83–96. Oslo. ISSN 0024–1164.
This research describes compositional variations within the shell of the extant mussel Mytilur edulis and proposes that they are produced by metabolic gradients within the shell‐secreting mantle. Because we have previously proposed that the same metabolic gradients are responsible for variations in shell form (curvature), we establish here a model for molluscan shell growth integrating. for the first time. shell form and composition with mantle metabolism. The electron microprobe was used to measure the distribution of Mg. S, and Ca in the outer calcitic shell layer of sectioned. polished, and either A1‐ or C‐coated shell. Mg/Ca and S/Ca ratios in the outer shell are respectively 1.25 and 1.40 times higher along slow‐growing, commissure‐umbo axes of high shell curvature and high metabolic activity than along rapidly growing axes of low curvature and low metabolic activity. The ratios within the inner surface of the calcitic shell layer decline most rapidly along commissure‐umbo axes where mantle metabolic activity also declines rapidly. We reject the null hypothesis, generally at high levels of significance (1‐tests. F‐tests. regression analyses, and discriminant analysis. with p 4 0.01) that there is no difference in either Mg or S concentration in sections of the calcitic shell layer that differ in shell curvature and mantle metabolic activity. We conclude that calcium (mineral)‐rich portions of shells are energctically less costly to produce than matrix or minor element‐rich portions. in agreement with the proposal that natural selection favors mineral‐rich shells because they are more efficient to produce than matrix‐rich shells. Among‐specimen differences are also highly significant (mixed model ANOVA). This confirms our assertion that paleontologists need to describe variations in skeletal composition among populations and throughout ontogeny as systematically as classical taxonomists describe morphology. if ever the environmental and the genetic influences on skeletal composition are to be distinguished. Bivalves. biomineralization, shell composition. magnesium, sulfur, calcium, metabolism, growth. Mytillus edulis
Male Wistar rats prelabeled with tetracycline to mark surfaces of bone and tooth formation-mineralization were placed into orbit for 18.5 days aboard the Soviet COSMOS-1129 Biosatellite. They were injected with tetracycline for a second and third time on the 6th and 27th days, respectively, after recovery of the Biosatellite. Spaceflight did not alter the rate of periosteal bone formation in the non-weight-bearing ribs and regions of the mandibles, which were covered by masticatory muscles. Bone formation-calcification rates were impaired at those sites in the jaw that had no contiguous muscle (molar region). The remodeling activity on the alveolar bone around the buccal roots of the molar teeth was significantly reduced but without creating a negative balance between formative and resorptive activities. Total Ca, P, and hydroxyproline concentrations in the jaws, incisors, and ribs were normal after spaceflight, but gravity density fractionation studies indicated that in the jaws alone, O-G conditions caused a delay in the maturation of bone mineral and matrix. A 29-day postflight recovery period at earth's gravity was sufficient to fully correct these anomalies. Relative to tooth formation, relatively normal circadian and infradian biorhythmic periodicities of Ca and P in dentin and enamel were maintained during spaceflight. We conclude that most of the non-weight-bearing bones of the rat skeleton are at risk to the effects of hypogravity.
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