Why do woodpeckers resist head impact injury: a biomechanical investigation

Head injury is a leading cause of morbidity and death in both industrialized and developing countries. It is estimated that brain injuries account for 15% of the burden of fatalities and disabilities, and represent the leading cause of death in young adults. Brain injury may be caused by an impact or a sudden change in the linear and/or angular velocity of the head. However, the woodpecker does not experience any head injury at the high speed of 6-7 m/s with a deceleration of 1000 g when it drums a tree trunk. It is still not known how woodpeckers protect their brain from impact injury. In order to investigate this, two synchronous high-speed video systems were used to observe the pecking process, and the force sensor was used to measure the peck force. The mechanical properties and macro/micro morphological structure in woodpecker's head were investigated using a mechanical testing system and micro-CT scanning. Finite element (FE) models of the woodpecker's head were established to study the dynamic intracranial responses. The result showed that macro/micro morphology of cranial bone and beak can be recognized as a major contributor to non-impact-injuries. This biomechanical analysis makes it possible to visualize events during woodpecker pecking and may inspire new approaches to prevention and treatment of human head injury.     

Sublingual structures in primates. Part 1: Prosimiae, Platyrrhini and Cercopithecinae

1. The sublingual structures of primates have been studied light-microscopically. There are 3 different sublingual structures in the species studied. The plica sublingualis occurs in all primates. The sublingual organ is a topographically modified plica sublingualis which occurs exclusively in Callicebus. A sublingua is present only in the prosimians. 2. The plica sublingualis contains the excretory ducts of the submandibular and sublingual salivary glands. The sublingua is ventrally adherent to the body of the tongue and is, with a few exceptions in Tupaia, characterized by a skeleton of cartilage tissue. A sublingua never exhibits excretory ducts or salivary glands. 3. In some Platyrrhini (Ateles, Aotus, Lagothrix, Alouatta, Callicebus), there are taste buds in the epithelium of the plica sublingualis. They are especially concentrated near the orifices of the salivary glands. 4. The fresh saliva of the submandibular and sublingual gland can be tested by the taste buds on the plica sublingualis, because there is a topographical coincidence. 5. There is a complete absence of taste buds at the plica sublingualis of the prosimians and the Cercopithecinae. 6. There are no taste buds in the epithelium of the sublingua. In the Lorisiformes and in the Lemuriformes the sublingua is a cleaning device of the anterior dentition, most probably in connection with a tactile sensibility. In the Tupaiformes and in the Tarsiiformes the sublingua is less developed. 7. There is no anatomical connection between the skeleton of cartilage tissue in the sublingua and the lytta, or the skeleton of the hyoideum. 8. In some Cercopithecinae (Macaca, Papio) a glandula apicis linguae is present.     

Reduction of adhesions with composite AlloDerm/polypropylene mesh implants for abdominal wall reconstruction

Ventral hernia repair often includes the use of structural prosthetic materials, such as polypropylene mesh, that can induce dense abdominal adhesions to peritoneal structures. AlloDerm (LifeCell Corp., Branchburg, N.J.), a commercially available decellularized human dermal analogue with its native basement membrane components intact, is gradually revascularized and replaced with autologous tissue after implantation. The authors hypothesized that AlloDerm integrated with polypropylene mesh would reduce adhesions and provide a biodegradable scaffold to generate an autologous vascularized tissue layer separating the abdominal viscera from the mesh. Ventral hernia defects (3 x 1 cm) in 19 guinea pigs were repaired using an inlay technique with polypropylene mesh alone (n = 6) or with composite implants constructed by integrating polypropylene mesh and AlloDerm with its basement membrane surface oriented toward (polypropylene/AlloIn, n = 7) or away from (polypropylene/ AlloOut, n = 6) the peritoneal cavity. At 4 weeks, the authors determined the amount of mesh implant surface area covered by adhesions, the strength of the adhesions [graded from 0 (none) to 3], and the incidence of bowel adhesions. Histologic analyses were performed on full-thickness tissue sections from the repair sites. The mean surface areas affected by adhesions and mean adhesion strength were significantly lower in the polypropylene/AlloIn (area, 12.4 percent; mean grade, 1.0) and polypropylene/AlloOut (area, 9.5 percent; mean grade, 0.5) groups than in the polypropylene group (area, 79.5 percent; mean grade, 2.9); there were no such differences between the polypropylene/AlloIn and polypropylene/AlloOut groups. The bowel was adherent to 67 percent of polypropylene repairs and 0 percent of the composite mesh repairs. The AlloDerm was remodeled to form a vascularized tissue layer beneath the mesh in composite repairs, unlike the significantly thinner, dense scar layer that formed in the polypropylene repairs. Immunohistochemical labeling for factor VIII showed neovascularization throughout the AlloDerm.The AlloDerm thus functioned as a biodegradable tissue scaffold, guiding the formation of a thick, well-vascularized tissue layer separating the polypropylene mesh from intraperitoneal structures. This significantly reduced both the amount of surface area covered by adhesions and adhesion strength. Basement membrane orientation had no effect. Composite mesh implants composed of structural prosthetic materials integrated with AlloDerm may have useful clinical applications for abdominal wall reconstruction by reducing adhesions and providing a vascularized tissue layer to separate and protect the peritoneal structures from polypropylene mesh fibers.     

Evidence for an elastic projection mechanism in the chameleon tongue

To capture prey, chameleons ballistically project their tongues as far as 1.5 body lengths with accelerations of up to 500 m s(-2). At the core of a chameleon's tongue is a cylindrical tongue skeleton surrounded by the accelerator muscle. Previously, the cylindrical accelerator muscle was assumed to power tongue projection directly during the actual fast projection of the tongue. However, high-speed recordings of Chamaeleo melleri and C. pardalis reveal that peak powers of 3000 W kg(-1) are necessary to generate the observed accelerations, which exceed the accelerator muscle's capacity by at least five- to 10-fold. Extrinsic structures might power projection via the tongue skeleton. High-speed fluoroscopy suggests that they contribute less than 10% of the required peak instantaneous power. Thus, the projection power must be generated predominantly within the tongue, and an energy-storage-and-release mechanism must be at work. The key structure in the projection mechanism is probably a cylindrical connective-tissue layer, which surrounds the entoglossal process and was previously suggested to act as lubricating tissue. This tissue layer comprises at least 10 sheaths that envelop the entoglossal process. The outer portion connects anteriorly to the accelerator muscle and the inner portion to the retractor structures. The sheaths contain helical arrays of collagen fibres. Prior to projection, the sheaths are longitudinally loaded by the combined radial contraction and hydrostatic lengthening of the accelerator muscle, at an estimated mean power of 144 W kg(-1) in C. melleri. Tongue projection is triggered as the accelerator muscle and the loaded portions of the sheaths start to slide over the tip of the entoglossal process. The springs relax radially while pushing off the rounded tip of the entoglossal process, making the elastic energy stored in the helical fibres available for a simultaneous forward acceleration of the tongue pad, accelerator muscle and retractor structures. The energy release continues as the multilayered spring slides over the tip of the smooth and lubricated entoglossal process. This sliding-spring theory predicts that the sheaths deliver most of the instantaneous power required for tongue projection. The release power of the sliding tubular springs exceeds the work rate of the accelerator muscle by at least a factor of 10 because the elastic-energy release occurs much faster than the loading process. Thus, we have identified a unique catapult mechanism that is very different from standard engineering designs. Our morphological and kinematic observations, as well as the available literature data, are consistent with the proposed mechanism of tongue projection, although experimental tests of the sheath strain and the lubrication of the entoglossal process are currently beyond our technical scope.     

Convergently evolved muscle architecture enables high-performance ballistic movement in salamanders

Elastically powered ballistic movements, such as tongue projection, are common in nature, likely due to benefits such as increased acceleration and distance of movement, and decreased thermal sensitivity imparted by elastic mechanisms. Within Plethodontidae, both muscle-powered and elastically powered ballistic tongue projection occur. Thus, we examine how elastically powered ballistic tongue projection morphology has evolved from muscle powered projection at the level of the projector muscles (m. subarcualis rectus [SAR]). We find that two main SAR morphologies have evolved within Plethodontidae. The first SAR morphology is conducive to elastically powered ballistic projection. This ballistic SAR morphology has evolved multiple, independent times within Plethodontidae, and results from the correlated evolution of several traits including increased collagen aponeuroses, larger SAR muscles, and the loss of inner myofibers attaching directly to the tongue skeleton. While the independent evolution of ballistic SAR morphology has arrived at a similar anatomical design, other tongue structures such as tongue attachment and skeleton folding type varies among species with a ballistic SAR morphology. The second morphology is conducive to muscle-powered projection and is similar to morphology found in an outgroup, Salamandridae. The SAR of these species have inner myofibers that attach to the tongue skeleton, limiting projection distance, coupled with reduced collagen aponeuroses present in relatively small projector muscles. This SAR morphology has likely been retained from ancestors or may be related to feeding ecology. Overall, a ballistic SAR morphology has evolved repeatedly and independently due to the correlated evolution of several SAR traits, including the loss of inner myofibers, which is likely a defining feature of ballistic projection.     

Highly nonrandom features of synaptic connectivity in local cortical circuits

How different is local cortical circuitry from a random network? To answer this question, we probed synaptic connections with several hundred simultaneous quadruple whole-cell recordings from layer 5 pyramidal neurons in the rat visual cortex. Analysis of this dataset revealed several nonrandom features in synaptic connectivity. We confirmed previous reports that bidirectional connections are more common than expected in a random network. We found that several highly clustered three-neuron connectivity patterns are overrepresented, suggesting that connections tend to cluster together. We also analyzed synaptic connection strength as defined by the peak excitatory postsynaptic potential amplitude. We found that the distribution of synaptic connection strength differs significantly from the Poisson distribution and can be fitted by a lognormal distribution. Such a distribution has a heavier tail and implies that synaptic weight is concentrated among few synaptic connections. In addition, the strengths of synaptic connections sharing pre- or postsynaptic neurons are correlated, implying that strong connections are even more clustered than the weak ones. Therefore, the local cortical network structure can be viewed as a skeleton of stronger connections in a sea of weaker ones. Such a skeleton is likely to play an important role in network dynamics and should be investigated further.     

Biomechanical and viscoelastic properties of skin,SMAS, and composite flaps as they pertain to rhytidectomy

Previous studies have focused on biomechanical and viscoelastic properties of the superficial musculoaponeurotic system (SMAS) flap and the skin flap lifted in traditional rhytidectomy procedures. The authors compared these two layers with the composite rhytidectomy flap to explain their clinical observations that the composite dissection allows greater tension and lateral pull to be placed on the facial and cervical flaps, with less long-term stress-relaxation and tissue creep. Eight fresh cadavers were dissected by elevating flaps on one side of the face and neck as skin and SMAS flaps and on the other side as a standard composite rhytidectomy flap. The tissue samples were tested for breaking strength, tissue tearing force, stress-relaxation, and tissue creep. For breaking strength, uniform samples were pulled at a rate of 1 inch per minute, and the stress required to rupture the tissues was measured. Tissue tearing force was measured by attaching a 3-0 suture to the tissues and pulling at the same rate as that used for breaking strength. The force required to tear the suture out of the tissues was then measured. Stress-relaxation was assessed by tensing the uniformly sized strips of tissue to 80 percent of their breaking strength, and the amount of tissue relaxation was measured at 1-minute intervals for a total of 5 minutes. This measurement is expressed as the percentage of tissue relaxation per minute. Tissue creep was assessed by using a 3-0 suture and calibrated pressure gauge attached to the facial flaps. The constant tension applied to the flaps was 80 percent of the tissue tearing force. The distance crept was measured in millimeters after 2 and 3 minutes of constant tension. Breaking strength measurements demonstrated significantly greater breaking strength of skin and composite flaps as compared with SMAS flaps (p < 0.05). No significant difference was noted between skin and composite flaps. However, tissue tearing force demonstrated that the composite flaps were able to withstand a significantly greater force as compared with both skin and SMAS flaps (p < 0.05). Stress-relaxation analysis revealed the skin flaps to have the highest degree of stress-relaxation over each of five 1-minute intervals. In contrast, the SMAS and composite flaps demonstrated a significantly lower degree of stress-relaxation over the five 1-minute intervals (p < 0.05). There was no difference noted between the SMAS flaps and composite flaps with regard to stress-relaxation. Tissue creep correlated with the stress-relaxation data. The skin flaps demonstrated the greatest degree of tissue creep, which was significantly greater than that noted for the SMAS flaps or composite flaps (p < 0.05). Comparison of facial flaps with cervical flaps revealed that cervical skin, SMAS, and composite flaps tolerated significantly greater tissue tearing forces and demonstrated significantly greater tissue creep as compared with facial skin, SMAS, and composite flaps (p < 0.05). These biomechanical studies on facial and cervical rhytidectomy flaps indicate that the skin and composite flaps are substantially stronger than the SMAS flap, allowing significantly greater tension to be applied for repositioning of the flap and surrounding subcutaneous tissues. The authors confirmed that the SMAS layer exhibits significantly less stress-relaxation and creep as compared with the skin flap, a property that has led aesthetic surgeons to incorporate the SMAS into the face lift procedure. On the basis of the authors' findings in this study, it seems that that composite flap, although composed of both the skin and SMAS, acquires the viscoelastic properties of the SMAS layer, demonstrating significantly less stress-relaxation and tissue creep as compared with the skin flap. This finding may play a role in maintaining long-term results after rhytidectomy. In addition, it is noteworthy that the cervical flaps, despite their increased strength, demonstrate significantly greater tissue creep as compared with facial flaps, suggesting earlier relaxation of the neck as compared with the face after rhytidectomy.     

用非离子去垢剂抽提获得的小游仆虫皮层细胞骨架的构形

由扫描电镜术显示,应用非离子去垢剂抽提获得的小游仆虫(Euplotes grocilis)皮层细胞骨架是由非纤毛区皮层骨架、纤毛器骨架及其附属纤维等构成的三维结构网架。各类细胞骨架以纤维物质为基本成分组成纤维网、纤维层、纤维束和纤维薄片等不同形态单元。其中：非纤毛区皮层骨架以表面纤维网和表膜下纤维层为形态单元位于细胞的外周层;纤毛器骨架中的口围带骨架、口侧膜骨架、额腹横棘毛骨架按各自的分布图式在皮层内定位,成为主要的皮层骨架结构。尽管这些纤毛器骨架显示不同的形态,但却具有相同的建构特征,即都是由纤毛器的毛基体、纤毛器托架和骨架附属纤维相互联系镶嵌在一起形成的相对独立的结构单元。分析推测,游仆虫皮层表面纤维网使细胞表面形成区域化结构,它也可能与细胞表面各部分的联系及其细胞与环境的相互作用有关;纤毛器骨架中各个纤毛器的毛基体复合结构可能对纤毛器托架和骨架附属纤维等起到微管组织中心的作用。     

Tongue evolution in the lungless salamanders, family plethodontidae. I. Introduction, theory and a general model of dynamics.

Plethodontid salamanders capture prey by projecting the tongue from the mouth. An analysis of theoretical mechanics of the hyobranchial skeleton is used to formulate a working hypothesis of tongue movements. Predictions that the skeletal elements of the tongue are included in the projectile and that the hyobranchial skeleton is folded during projection are central to the analysis. When decapitated in a particular way, salamanders project the tongue, and it is not retracted. When these heads are fixed and sectioned, examination confirms the predications. In turn, these observations are used to refine the working hypothesis and to generate a general model of tongue dynamics for plethodontids. Muscles performing the major roles of projection (subarcualis rectus I) and retraction (rectus cervicis profundus) are identified. The skeleton is folded passively along a morphological track having the form of a tractrix. Predictions concerning the shape of the track and the exact configuration of the folded skeleton are confirmed by study of sectioned material. The skeleton unfolds along the track during retraction and is spread into the resting state. The model developed herein will be used as a basis for predictions concerning selection patterns in the family and for analytical purposes in comparative and evolutionary studies.     

The connective tissue skeleton in the mammalian kidney and its innervation.

A special reticular basket-like system of connective tissue strips (called connective tissue skeleton - CTS) was found between the cortex and medulla in the kidney of various mammals. It enlarges the wall of the renal calyx (or pelvis) into the parenchyma. The main component of this system is collagen. A small amount of smooth muscle cells was found in one part of CTS srips situated around the papilla (the levator fornicis muscle). A dense monoaminergic and scanty cholinergic innervation was found in the whole system of the CTS. The functional importance of this system is discussed: (i) a tightly linked connection between the urine-discharging system and the kidney, (ii) 'milking' and similar effects in the papilla as well as perception of intrapelvic and intrarenal pressure, (iii) penetration of infection into the kidney and (iv) liberation of the monoaminergic transmitter.     

Preparative high-performance liquid chromatographic separation of proteins with HyperD ion-exchange supports

HyperD ion-exchange media combine the mechanical strength of a rigid polystyrene-mineral composite skeleton with the high protein-binding capacity of a three-dimensional soft gel located inside the skeleton. The skeleton solid matrix is completely filled with functionalized, highly hydrophilic, chemically stable ion-exchange hydrogels. These materials gave very efficient columns for protein separation with superior dynamic capacity, high resolving power and excellent protein recovery. Various protein mixtures were used to study the chromatographic performance of these new stationary phases. Comparisons between different particle size packing materials demonstrated the potential of this ion-exchange material for use on a large scale.     

Numerical assessment of thermal response associated with in vivo skin electroporation: the importance of the composite skin model

Electroporation is an approach used to enhance transdermal transport of large molecules in which the skin is exposed to a series of electric pulses. The structure of the transport inhibiting outer layer, the stratum corneum, is temporarily destabilized due to the development of microscopic pores. Consequently agents that are ordinarily unable to pass into the skin are able to pass through this outer barrier. Of possible concern when exposing biological tissue to an electric field is thermal tissue damage associated with Joule heating. This paper shows the importance of using a composite model in calculating the electrical and thermal effects associated with skin electroporation. A three-dimensional transient finite-volume model of in vivo skin electroporation is developed to emphasize the importance of representing the skin's composite layers and to illustrate the underlying relationships between the physical parameters of the composite makeup of the skin and resulting thermal damage potential.     

Muscle‐induced loading as an important source of variation in craniofacial skeletal shape

The shape of the craniofacial skeleton is constantly changing through ontogeny and reflects a balance between developmental patterning and mechanical‐load‐induced remodeling. Muscles are a major contributor to producing the mechanical environment that is crucial for “normal” skull development. Here, we use an F₅ hybrid population of Lake Malawi cichlids to characterize the strength and types of associations between craniofacial bones and muscles. We focus on four bones/bone complexes, with different developmental origins, alongside four muscles with distinct functions. We used micro‐computed tomography to extract 3D information on bones and muscles. 3D geometric morphometrics and volumetric measurements were used to characterize bone and muscle shape, respectively. Linear regressions were performed to test for associations between bone shape and muscle volume. We identified three types of associations between muscles and bones: weak, strong direct (i.e., muscles insert directly onto bone), and strong indirect (i.e., bone is influenced by muscles without a direct connection). In addition, we show that although the shape of some bones is relatively robust to muscle‐induced mechanical stimulus, others appear to be highly sensitive to muscular input. Our results imply that the roles for muscular input on skeletal shape extend beyond specific points of origin or insertion and hold significant potential to influence broader patterns of craniofacial geometry. Thus, changes in the loading environment, either as a normal course of ontogeny or if an organism is exposed to a novel environment, may have pronounced effects on skeletal shape via near and far‐ranging effects of muscular loading.     

Dogfish egg case structural studies by ATR FT-IR and FT-Raman spectroscopy

The dogfish egg case is a composite structure that combines mechanical tensile strength, toughness and elasticity with high permeability to small molecules and ions. Presumably, it provides both a protective and a filtering role for the egg/embryo contained within it. In this work, we performed structural studies of the Galeus melastomus egg case at two different stages of the hardening process, utilizing ATR FT-IR and FT-Raman spectroscopy. Based on these data we deduce that: (a) The G. melastomus egg case, in close analogy to that of the related species Scyliorhinus cunicula, is a complex, composite structure which consists mainly of an analogue of collagen IV. This network forming protein appears to have common secondary structural characteristics in the entire egg case. (b) The outermost layer of the non-sclerotized egg case is especially rich in tyrosine, while the innermost layer is rich in polysaccharides, presumably glycosaminoglycans, and lipids. These differences are diminished upon hardening. (c) Disulfide bonds do not appear to play a significant role in cross-linking. However, cross-links involving tyrosine residues appear to sclerotize the egg case. It is proposed that the intensity of the Raman band at ca. 1615 cm(-1), which is due to ring stretching vibrations of Tyr, might be a useful indicator of the sclerotization status of a certain proteinaceous tissue, when tyrosines are involved in sclerotization mechanisms.     

Histology of the heterostracan dermal skeleton: Insight into the origin of the vertebrate mineralised skeleton

Living vertebrates are divided into those that possess a fully formed and fully mineralised skeleton (gnathostomes) versus those that possess only unmineralised cartilaginous rudiments (cyclostomes). As such, extinct phylogenetic intermediates of these living lineages afford unique insights into the evolutionary assembly of the vertebrate mineralised skeleton and its canonical tissue types. Extinct jawless and jawed fishes assigned to the gnathostome stem evidence the piecemeal assembly of skeletal systems, revealing that the dermal skeleton is the earliest manifestation of a homologous mineralised skeleton. Yet the nature of the primitive dermal skeleton, itself, is poorly understood. This is principally because previous histological studies of early vertebrates lacked a phylogenetic framework required to derive evolutionary hypotheses. Nowhere is this more apparent than within Heterostraci, a diverse clade of primitive jawless vertebrates. To this end, we surveyed the dermal skeletal histology of heterostracans, inferred the plesiomorphic heterostracan skeleton and, through histological comparison to other skeletonising vertebrate clades, deduced the ancestral nature of the vertebrate dermal skeleton. Heterostracans primitively possess a four‐layered skeleton, comprising a superficial layer of odontodes composed of dentine and enameloid; a compact layer of acellular parallel‐fibred bone containing a network of vascular canals that supply the pulp canals (L1); a trabecular layer consisting of intersecting radial walls composed of acellular parallel‐fibred bone, showing osteon‐like development (L2); and a basal layer of isopedin (L3). A three layered skeleton, equivalent to the superficial layer L2 and L3 and composed of enameloid, dentine and acellular bone, is possessed by the ancestor of heterostracans + jawed vertebrates. We conclude that an osteogenic component is plesiomorphic with respect to the vertebrate dermal skeleton. Consequently, we interpret the dermal skeleton of denticles in chondrichthyans and jawless thelodonts as independently and secondarily simplified. J. Morphol. 276:657–680, 2015. © 2015 The Authors Journal of Morphology Published by Wiley Periodicals, Inc.     

Functional morphology of Tethya species (Porifera): 2. Three-dimensional morphometrics on spicules and skeleton superstructures of T. minuta

The biomechanics of body contraction in Porifera is almost unknown, although sponge contraction has been observed already in ancient times. Some members of the genus Tethya represent the most contractile poriferan species. All of them show a highly ordered skeleton layout. Based on three main spicule types, functional units are assembled, termed skeleton superstructures here. Using synchrotron radiation based x-ray microtomography and quantitative image analysis with specially developed particle and structure recognition algorithms allowed us to perform spatial allocation and 3D-morphometric characterizations of single spicules and skeleton superstructures in T. minuta. We found and analyzed three skeleton superstructures in the investigated specimen: (1) 85 megasclere bundles, (2) a megaster sphere, composed by 16,646 oxyasters and (3) a pinacoderm–tylaster layer composed by micrasters. All three skeleton superstructures represent composite materials of siliceous spicules and extracellular matrix. From structure recognition we developed an abstracted mathematical model of the bundles and the sphere. In addition, we analyzed the megaster network interrelation topology and found a baso-apical linear symmetry axis for the megaster density inside the sphere. Based on our results, we propose a hypothetical biomechanical contraction model for T. minuta and T. wilhelma, in which the skeleton superstructures restrain physical stress generated by contraction in the tissue. While skeletal structures within the genus Tethya have been explained using R. Buckminster Fullers principle of tensegrity by other authors, we prefer material science based biomechanical approaches, to understand skeletal superstructures by referring to their composite material properties.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Gender-related differences in the apparent timing of skeletal density bands in the reef-building coral Siderastrea siderea

Density banding in skeletons of reef-building corals is a valuable source of proxy environmental data. However, skeletal growth strategy has a significant impact on the apparent timing of density-band formation. Some corals employ a strategy where the tissue occupies previously formed skeleton during as the new band forms, which leads to differences between the actual and apparent band timing. To investigate this effect, we collected cores from female and male colonies of Siderastrea siderea and report tissue thicknesses and density-related growth parameters over a 17-yr interval. Correlating these results with monthly sea surface temperature (SST) shows that maximum skeletal density in the female coincides with low winter SSTs, whereas in the male, it coincides with high summer SSTs. Furthermore, maximum skeletal densities in the female coincide with peak Sr/Ca values, whereas in the male, they coincide with low Sr/Ca values. Both results indicate a 6-month difference in the apparent timing of density-band formation between genders. Examination of skeletal extension rates also show that the male has thicker tissue and extends faster, whereas the female has thinner tissue and a denser skeleton—but both calcify at the same rate. The correlation between extension and calcification, combined with the fact that density banding arises from thickening of the skeleton throughout the depth reached by the tissue layer, implies that S. siderea has the same growth strategy as massive Porites, investing its calcification resources into linear extension. In addition, differences in tissue thicknesses suggest that females offset the greater energy requirements of gamete production by generating less tissue, resulting in differences in the apparent timing of density-band formation. Such gender-related offsets may be common in other corals and require that environmental reconstructions be made from sexed colonies and that, in fossil corals where sex cannot be determined, reconstructions must be duplicated in different colonies.     

The stromatoporoid animal revisited: Building the skeleton

Modern coralline sponges secrete a skeleton by means of a basal pinacoderm, intracellularly, or inside the soft tissue on an organic matrix The examination of terminal growth surfaces of stromatoporoids indicates that soft tissue in laminate and amalgamate forms occupied the upper galleries and that the skeletal elements were secreted within the soft tissue on an organic matrix. The stromatoporellids and clathrodictyids secreted the skeleton in modules that are homologous to the chambers of a sphinctozoan. In stromatoporellids the module was bounded by a floor that formed the upper layer of the tripatite lamina below and a roof that became the lower layer of the next lamina; it further included the intervening pillars. In clathrodictyids the module had only a roof and pillars, and the laminae are single layers. other stromatoporoids may have secreted their skeletons at the base of the soft tissue and had minimal occupation of the skeleton. *** Stromatoporoid, sphinctozoa, sclerospongiae, sponge, paleobiology.     

Fat and bone

Body weight is a principal determinant of bone density and fracture risk, and adipose tissue mass is a major contributor to this relationship. In contrast, some recent studies have argued that “fat mass after adjustment for body weight” actually has a deleterious effect on bone, but these analyses are confounded by the co-linearity between the variables studied, and therefore have produced misleading results. Mechanistically, fat and bone are linked by a multitude of pathways, which ultimately serve the function of providing a skeleton appropriate to the mass of adipose tissue it is carrying. Adiponectin, insulin/amylin/preptin, leptin and adipocytic estrogens are all likely to be involved in this connection. In the clinic, the key issues are that obesity is protective against osteoporosis, but underweight is a major preventable risk factor for fractures.