Microstructure and energy dispersive diffraction reconstruction of 3D patterns of crystallographic texture in a shark centrum.

Purpose: Tomography using diffracted x-rays produces reconstructions mapping quantities such as crystal lattice parameter(s), crystallite size, and crystallographic texture, information quite different from that obtained with absorption or phase contrast. Diffraction tomography is used to map an entire blue shark centrum with its double cone structure (corpora calcerea) and intermedialia (four wedges). Approach: Energy dispersive diffraction (EDD) and polychromatic synchrotron x-radiation at 6-BM-B, the Advanced Photon Source, were used. Different, properly oriented Bragg planes diffract different x-ray energies; these intensities are measured by one of ten energy-sensitive detectors. A pencil beam defines the irradiated volume, and a collimator before each energy-sensitive detector selects which portion of the irradiated column is sampled at any one time. Translating the specimen along X , Y , and Z axes produces a 3D map. Results: We report 3D maps of the integrated intensity of several bioapatite reflections from the mineralized cartilage centrum of a blue shark. The c axis reflection's integrated intensities and those of a reflection with no c axis component reveal that the cone wall's bioapatite is oriented with its c axes lateral, i.e., perpendicular to the backbone's axis, and that the wedges' bioapatite is oriented with its c axes axial. Absorption microcomputed tomography (laboratory and synchrotron) and x-ray excited x-ray fluorescence maps provide higher resolution views. Conclusion: The bioapatite in the cone walls and wedges is oriented to resist lateral and axial deflections, respectively. Mineralized tissue samples can be mapped in 3D with EDD tomography and subsequently studied by destructive methods.

Shark centra microanatomy and mineral density variation studied with laboratory microComputed Tomography.

Centra of shark vertebrae from three species of Lamniformes (Alopias vulpinus, Carcharodon carcharias and Isurus oxyrinchus) and three species of Carcharhiniformes (Carcharhinus plumbeus, Carcharhinus obscurus and Prionace glauca) were imaged with laboratory microcomputed Tomography (microCT) using volume element (voxel) sizes between 16 and 24 µm. Linear attenuation coefficients were the same in the corpus calcarea (hour-glass-shaped cone) and intermedialia of the lamniforms but were smaller in the intermedialia than in the corpus calcarea of the carcharhiniforms. All centra contained growth bands which were visible as small changes in linear attenuation coefficient. In all six cases, the cross-sections of the cones were close to circular, and the cone angles matched those reported in the literature. Cartilage canals were a prominent structure in the intermedialia of all species, 3D renderings of centra of C. obscurus and I. oxyrinchus diameters showed these canals ran radially outward from the cone walls, and canal diameters were consistent with the limited numerical values in the literature. Somewhat higher calcification levels around the periphery of cartilage canals and of outer surfaces of the intermedialia and corpus calcerea suggest microstructural variation exists at scale below that which can be resolved in the present data sets.

Vertebral growth and band-pair deposition in sexually mature little skates Leucoraja erinacea: is adult band-pair deposition annual?

Mature male and female little skates Leucoraja erinacea were injected with oxytetracycline and maintained in captivity for 13 months to assess centrum growth and the frequency of band-pair deposition. Sixty per cent of the individuals analysed did not deposit a full band pair over the 13 month period. Thus, a majority of captive skates did not exhibit annual band-pair deposition. Previous research confirms annual band-pair deposition in all juvenile and most adult L. erinacea, therefore sexual maturation may lead to decreased frequency of band-pair formation. Age underestimation of larger, older elasmobranchs is being identified in an increasing number of elasmobranch species including L. erinacea as demonstrated in this study. The effect of age underestimation from band-pair counts on studies that use age-based characteristics needs to be addressed.

Improved estimation of intrinsic growth r(max) for long-lived species: integrating matrix models and allometry.

Intrinsic population growth rate (r(max)) is an important parameter for many ecological applications, such as population risk assessment and harvest management. However, r(max) can be a difficult parameter to estimate, particularly for long-lived species, for which appropriate life table data or abundance time series are typically not obtainable. We describe a method for improving estimates of r(max) for long-lived species by integrating life-history theory (allometric models) and population-specific demographic data (life table models). Broad allometric relationships, such as those between life history traits and body size, have long been recognized by ecologists. These relationships are useful for deriving theoretical expectations for r(max), but r(max) for real populations may vary from simple allometric estimators for "archetypical" species of a given taxa or body mass. Meanwhile, life table approaches can provide population-specific estimates of r(max) from empirical data, but these may have poor precision from imprecise and missing vital rate parameter estimates. Our method borrows strength from both approaches to provide estimates that are consistent with both life-history theory and population-specific empirical data, and are likely to be more robust than estimates provided by either method alone. Our method uses an' allometric constant: the product of r(max) and the associated generation time for a stable-age population growing at this rate. We conducted a meta-analysis to estimate the mean and variance of this allometric constant across well-studied populations from three vertebrate taxa (birds, mammals, and elasmobranchs) and found that the mean was approximately 1.0 for each taxon. We used these as informative Bayesian priors that determine how much to "shrink" imprecise vital rate estimates for a data-limited population toward the allometric expectation. The approach ultimately provides estimates of r(max) (and other vital rates) that reflect a balance of information from the individual studied population, theoretical expectation, and meta-analysis of other populations. We applied the method specifically to an archetypical petrel (representing the genus Procellaria) and to white sharks (Carcharodon carcharias) in the context of estimating sustainable-fishery bycatch limits.