Changes in egg shell characteristics of the Sparrowhawk (Accipiter nisus) and Peregrine (Falco peregrinus) associated with exposure to environmental pollutants during recent decades

In Britain since the late 1940s, the Sparrowhawk ( Accipiter nisus ) and Peregrine (Falco peregrinus) have laid eggs with unusually thin shells. DDT and its metabolites have been blamed. This paper reports how various properties of modern shells differ from those of older shells of normal thickness.
For the shells of both species, there were roughly proportional reductions in thickness of the two main component layers, the mammillary and palisade layers, suggesting that thin shells resulted from a decreased rate of deposition. In addition, in modern Sparrowhawk shells, the resistant surface layer was especially deficient perhaps due to a further reduction in deposition rate or to slight premature termination. Shell thinning was associated with a proportionately greater decrease in shell strength. For the Peregrine, porosity, measured as the rate of passage of water vapour, was lower for the thin shells than for normal shells. This difference could not be explained by a change in the area of the pore channels, since the modern shells did not have fewer pores and the pore channels were the same size and shape in the two samples of shells. However, in the thin shells of both species, mammillae height increased relative to mammillary layer thickness, and in the Peregrine shells the extent of this increase was related to the change in porosity.     

Soluble organic matrices of the calcitic prismatic shell layers of two Pteriomorphid bivalves. Pinna nobilis and Pinctada margaritifera

The calcitic prisms of the shells of two bivalves, Pinna and Pinctada, are considered simple prisms according to some morphological and mineralogical characteristics. Scanning electron microscopic and atomic force microscopic studies show that the microstructures and nanostructures of these two shells are different. Pinna prisms are monocrystalline, whereas Pinctada prisms are not. Moreover, intraprismatic membranes are present only in the Pinctada prisms. The soluble organic matrices extracted from these prisms are acidic, but their bulk compositions differ. Ultraviolet and infrared spectrometries, fluorescence, high pressure liquid chromatography, and electrophoresis show that the sugar-protein ratios and the molecular weights are different. Sulfur is mainly associated with acidic sulfated sugars, not with amino acids, and the role of acidic sulfated sugars is still underestimated. Thus, the simple prism concept is not a relevant model for the biomineralization processes in the calcitic prismatic layer of mollusk shells.     

The effect of lipids on the adherence of axillary aerobic coryneform bacteria

AIMS: A wide range of lipids are present on the skin surface of human beings and bacterial lipases are known to modify them. The microflora of the underarm (axilla) is often dominated by aerobic coryneforms and whilst many require lipids for growth, they appear not to be utilized as carbon sources. The aim of this study was to investigate the adherence aerobic coryneforms to lipids present on the skin surface of the human axilla to determine whether they contribute to colonization of the skin. METHODS: Aerobic coryneforms were grown in a defined synthetic medium in the presence of (14)C-glucose to produce radio-labelled cells. Adherence to lipids was tested using a thin layer chromatography plate-based assay. SIGNIFICANCE AND IMPACT OF THE STUDY: The mechanism of bacterial adhesion to skin lipids is unknown. The results of this study show that a significant proportion of cutaneous aerobic coryneform isolates from the axilla interact with skin lipids resulting in increased adherence, which may contribute to skin colonization.     

A study of the egg shells of the Falconiformes

A study of a selection of egg shells of the Falconiformes has been made similar to the earlier ones on ratites, the Anatidae and the Sphenisciformes. Chemical analyses, and histological and plastic embedding techniques were used.
The main part of the shell in all species studied consists of large crystals running through the shell. There was no layer of fine vertical crystals above this and no cover, and even the cuticle was not very pronounced. Histological studies showed no major differences, except that some shells had vacuoles in the outer layers. All such shells also gave an unetched outer layer when plastic embedded radial sections were studied and thin sections showed spaces between and within crystals. These spaces in the outer layers of the shell were of taxonomic interest for they were not present in the Cathartidae, the Falconidae and Sagittarius serpentarius.
Pore channels appeared to be much sparser than in other orders so far studied and all pores were single. Pigment was present on the surface of some shells, but it was also found in different layers of the shell right down to the cone layer and, in one case, had leaked through on to the membrane.
There were significant relationships between total and soluble shell nitrogen which divided the Falconidae from most of the Accipitridae but left Pernis and Pandion in an intermediate position.     

Glucosyl diglyceride lipid structures in Deinococcus radiodurans.

The structures of two lipids from the radiation-resistant bacterium Deinococcus radiodurans are reported here: 1,2-diacyl-3-alpha-glucopyranosyl-glycerol and 3-O-[6'-O-(1",2"-diacyl- 3"-phosphoglycerol)-alpha-glucopyranosyl]-1,2-diacylglycerol. These lipids are strikingly different from previously characterized polar lipids from this organism, in that they are not unique to the genus Deinococcus and indeed have counterparts in both gram-negative and gram-positive bacteria. Moreover, as examples of glucose-containing lipids, they further illustrate the diversity of carbohydrate-containing lipids in D. radiodurans, from which lipids containing galactose and N-acetylglucosamine have already been structurally characterized.     

SHELL MICROSTRUCTURE OF GASTROPODS FROM LAKE TANGANYIKA,AFRICA: ADAPTATION,CONVERGENT EVOLUTION,AND ESCALATION

Gastropod shells from Lake Tanganyika, with their heavy calcification, coarse noded ribbing, spines, apertural lip thickening and repair scars, resemble marine shells more closely than they resemble other lacustrine shells. This convergence between Tanganyikan and marine gastropod shells, however, is not just superficial. Scanning electron microscope (SEM) studies reveal that the Tanganyikan shells are primarily layers of crossed-lamellar crystal architecture (that is, needle-like aragonite crystals arranged into laths that are packed into sheets such that the aragonite needles of adjacent laths are never parallel). The number of crossed-lamellar layers can vary from one to four between different Tanganyikan gastropod species. In species with two or more crossed-lamellar layers, the orientation of the lamellae is offset by approximately 90° between the different layers. The number of crossed-lamellar layers in the shell wall is positively correlated with shell strength and with predation resistance. Three and four crossed-lamellar layers in the shell wall evolved several times independently within the endemic thiarid gastropod radiation in Lake Tanganyika. Repeated origins of three and four crossed-lamellar layers suggest that they may be specific adaptations by Tanganyikan gastropods to strengthen their shells as a defense against shell-crushing predators.     

A Comparative Study of the Shell Matrix Protein Aspein in Pterioid Bivalves

Aspein is one of the unusually acidic shell matrix proteins originally identified from the pearl oyster Pinctada fucata. Aspein is thought to play important roles in the shell formation, especially in calcite precipitation in the prismatic layer. In this study, we identified Aspein homologs from three closely related pterioid species: Pinctada maxima, Isognomon perna, and Pteria penguin. Our immunoassays showed that they are present in the calcitic prismatic layer but not in the aragonitic nacreous layer of the shells. Sequence comparison showed that the Ser-Glu-Pro and the Asp-Ala repeat motifs are conserved among these Aspein homologs, indicating that they are functionally important. All Aspein homologs examined share the Asp-rich D-domain, suggesting that this domain might have a very important function in calcium carbonate formation. However, sequence analyses showed a significantly high level of variation in the arrangement of Asp in the D-domain even among very closely related species. This observation suggests that specific arrangements of Asp are not required for the functions of the D-domain.     

Structure and composition of the boundary zone between aragonitic crossed lamellar and calcitic prism layers in the shell of Concholepas concholepas (Mollusca,Gastropoda)

Mollusc shells are composed of two or three layers. The main layers are well‐studied, but the structural and chemical changes at their boundaries are usually neglected. A microstructural, mineralogical, and biochemical study of the boundary between the inner crossed lamellar and outer prismatic layers of the shell of Concholepas concholepas showed that this boundary is not an abrupt transition. Localized structural and chemical analyses showed that patches of the inner aragonitic crossed lamellar layer persist within the outer calcitic prismatic layer. Moreover, a thin aragonitic layer with a fibrous structure is visible between the two main layers. A three‐step biomineralization process is proposed that involves changes in the chemical and biochemical composition of the last growth increments of the calcite prisms. The changes in the secretory process in the mantle cells responsible for the shell layer succession are irregular and discontinuous.     

Avoidance of drilled gastropod shells by the hermit crab Pagurus longicarpus at Nahant, Massachusetts

Most hermit crabs depend on empty gastropod shells for shelter; competition for appropriate shells is often severe. This study determined whether shells that have been drilled by naticid gastropods are suitable for occupancy by the hermit crab Pagurus longicarpus. Differences in the characteristics of empty shells and those occupied by hermit crabs were assessed at two adjacent field sites in Nahant, Massachusetts. Drilling damage was far more frequent in empty gastropod shells than in shells occupied by hermit crabs, suggesting that individuals of P. longicarpus avoid drilled shells. They did not appear to avoid shells with other forms of damage. Laboratory experiments confirmed that these hermit crabs preferentially chose intact shells over drilled shells, even when the intact shells offered were most suitable for crabs half the weight of those tested. Final shell choices were generally made within 1 h. The hermit crabs apparently discriminated between intact and drilled shells based on tactile cues, since crabs kept in the dark showed the same preference for intact shells. The hermit crabs strongly avoided, to nearly the same extent, artificially drilled shells, naturally drilled shells, and shells with holes artificially drilled on the opposite side of the shell from where they would normally be located. Possible selective forces causing P. longicarpus to show such strong behavioral avoidance of drilled shells include increased vulnerability of crabs in drilled shells to osmotic stress, predation, and eviction by conspecifics.     

Mineralogy of shells from two freshwater snails Belgrandiella fontinalis and B kuesteri

X-ray powder diffraction (XRD) was used to study the mineral composition of shells of snails Belgrandiella fontinalis and Belgrandiella kuesteri collected from three freshwater springs in northeastern Slovenia. The fractions of aragonite, calcite, dolomite and quartz in particular shells were determined. The analysed shells consisted of two or more distinct inorganic layers. The outer shell layer for both species and all sampling localities contained aragonite. The outer layer of B. fontinalis collected at one locality, also contained a small fraction of calcite ( approximately 1 molar%) besides the dominant aragonite. Calcite was identified in the inner layer(s) of both species (2 to 3 molar%), while quartz was found only in B. kuesteri (5-7 molar%). However, both species sampled at one locality showed the presence of dolomite (approx. 20 molar%) in the inner layer(s). The presence of dolomite in the shells of adult gastropods and even molluscs is unusual. A possible formation mechanism and specific ecological factor that could influence the precipitation of dolomite in the shells of different Belgrandiella species is discussed.     

Do predatory drill holes influence the transport and deposition of gastropod shells?

Predatory gastropod drill holes are an abundant and easily identifiable signal of predation in ancient and modern molluscan shell assemblages. Many workers have used drill holes to interpret patterns of predation intensity and success in fossil assemblages. These studies are predicated on the assumption that the relative abundances of drilled and undrilled shells in an assemblage accurately reflect those of the community from which the shells were originally derived. The underlying assumption is that drilled and undrilled shells are transported into shell accumulations in the same manner. If this assumption is false, shell accumulations do not represent taphonomically unbiased samples, but rather preferentially sorted deposits from which conclusions about drilling predation cannot be made. To test the hypothesis that drilled and undrilled gastropod shells transport at different flow velocities, multiple transport trials were conducted on two morphologically distinct taxa, Olivella biplicata and Euspira lewisii. Individual specimens were placed in a recirculating flume tank and observed from rest (in stable orientation) until they were transported downstream. During each trial, flow velocity was slowly and incrementally increased, so as to avoid pulses of acceleration, until shells began to move downstream. Drilled and undrilled specimens of both taxa demonstrate statistically significant correlations between shell mass and average transport velocity. Similarly sized drilled and undrilled specimens of both taxa do not exhibit significant differences in transport velocity. These results indicate that predatory drill holes do not change the hydrodynamic properties of gastropod shells. Therefore, gastropod shell assemblages are not likely to be affected by differential transport and sorting of drilled and undrilled shells.     

Structural and biochemical properties of lipid particles from the yeast Saccharomyces cerevisiae

The two most prominent neutral lipids of the yeast Saccharomyces cerevisiae, triacylglycerols (TAG) and steryl esters (SE), are synthesized by the two TAG synthases Dga1p and Lro1p and the two SE synthases Are1p and Are2p. In this study, we made use of a set of triple mutants with only one of these acyltransferases active to elucidate the contribution of each single enzyme to lipid particle (LP)/droplet formation. Depending on the remaining acyltransferases, LP from triple mutants contained only TAG or SE, respectively, with specific patterns of fatty acids and sterols. Biophysical investigations, however, revealed that individual neutral lipids strongly affected the internal structure of LP. SE form several ordered shells below the surface phospholipid monolayer of LP, whereas TAG are more or less randomly packed in the center of the LP. We propose that this structural arrangement of neutral lipids in LP may be important for their physiological role especially with respect to mobilization of TAG and SE reserves.     

Resistance to shell breaking in two intertidal snails

The ability of shells to withstand shell breaking forces has been examined in two intertidal prosobranchs, Nucella lapillus and Littorina littorea , using four methods: measuring shell strength on a compressive testing machine, measuring the shell to body mass ratio, measuring the shell thickness and measuring the ability of crabs to break shells in aquarium experiments. Nucella lapillus consistently showed a relationship between shell vulnerability and environmental variables: the shells were easier to break at sites where rock and boulder movement was the least. Although some between-site differences were found in L. littorea shells, these were less than in N. lapillus and did not relate to environment variables: the shells were easier to break at sites where exposure to wave action was the least. Although some between-site differences were found in L. littorea shells , these were less than in N. lapillus and did not relate to environmental factors. However, both species appear to grow into a size refuge in which they are secure from predation by shore crabs at the sites where these crabs are commonest.     

Variability of shell repair in the Manila clam Ruditapes philippinarum affected by the Brown Ring Disease: a microstructural and biochemical study

For more than two decades, the Manila clam Ruditapes philippinarum has been regularly affected by Brown Ring Disease (BRD), an epizootic event caused by the bacterium Vibrio tapetis and characterized by the development of a brown deposit on the inner face of valves. Although BRD infection is often lethal, some clams recover by mineralizing a new repair shell layer, which covers the brown deposit and fully isolates it from living tissues. In order to understand this specific shell repair process, the microstructures of repaired zones were compared to those of shells unaffected by BRD. In addition, the organic matrix associated with unaffected shells and to repair patches were extracted and compared by biochemical and immunological techniques. Our results show that the repaired zones exhibit microstructures that resemble the so-called homogeneous microstructure of the internal layer, with some marked differences, like the development of crossed-acicular crystals, which form chevron-like patterns. In the three tested batches of repaired layers, the matrices exhibit certain heterogeneity, i.e., they are partially to widely different from the ones of shells unaffected by BRD, as illustrated by SDS-PAGE and by serological comparisons. Our results strongly suggest a modification of the secretory regime of calcifying mantle cells during the shell repair process. Polyclonal antibodies, which were developed against specific protein fractions of the shell, represent relevant tools for localizing by immunohistology the cells responsible for the repair.     

Multiscale Mechanics and Optimization of Gastropod Shells

A vast majority of mollusks grow a hard shell for protection.The structure of these shells comprises several levels of hierarchy that increase their strength and their resistance to natural threats.This article focuses on nacreous shells,which are composed of two distinct layers.The outer layer is made of calcite,which is a hard but brittle material,and the inner layer is made of nacre,a tough and ductile material.The inner and outer layers are therefore made of materials with distinct structures and properties.In this article,we demonstrate that this system is optimum to defeat attacks from predators.A two-scale modeling and optimization approach was used.At the macroscale,a two-layer finite element model of a seashell was developed to capture shell geometry.At the microscale,a representative volume element of the microstructure of nacre was used to model the elastic modulus of nacre as well as a multiaxial failure criterion,both expressed as function of microstructural parameters.Experiments were also performed on actual shells of red abalone to validate the results obtained from simulations and gain insight into the way the shell fails under sharp perforation.Both optimization and experimental results revealed that the shell displays optimum performance when two modes of failure coincide within the structure.Finally,guidelines for designing two-layer shells were proposed to improve the performance of engineered protective systems undergoing similar structural and loading conditions.     

The nature of the adhesion of tentacles to shells during shell-climbing in the sea anemone Calliactis parasitica (Couch)

Phase contrast microscopy and scanning electron microscopy show that during the response of the symbiotic sea anemone Calliactis parasitica (Couch) to shells of Buccinum undatum (L.) three times as many spirocysts as nematocysts are discharged. Observations indicate that spirocysts are responsible for the adhesion of tentacles to shells.Discharge levels are not significantly influenced by the nature of the substratum to which the anemones are attached. The reported observation that fewer tentacles adhere to shells when anemones are settled on shells than when they are fixed on a different substratum is re-interpreted in terms of a new model for the control of spirocyst discharge.     

Tyrosinase localization in mollusc shells

In molluscan shellfish, pigmentation is frequently observed in the calcified shell, but the molecular basis of this process is not understood. Here, we report two tyrosinase proteins (Pfty1 and Pfty2) found in the prismatic shell layer of the pearl oyster Pinctada fucata; this layer is recognized as the pigmented region in P. fucata. The protein sequences were deduced from the corresponding cDNAs and confirmed by MALDI-TOF/TOF analysis. The sequences suggest that both tyrosinases have two copper-binding sites in similar N-terminal domains that are homologous to tyrosinases of cephalopods and hemocyanins of gastropods. In turn, this suggests that bivalve tyrosinases are evolved from a common ancestral copper-binding protein in the mollusc. Pfty1 and Pfty2 were specifically expressed in the mantle, and their expression in the mantle is different from each other, suggesting that these tyrosinases have distinctive roles in melanogenesis in shells.     

Antipredator defence of the hermit crab Pagurus filholi induced by predatory crabs

Hermit crabs have two antipredator tactics: taking refuge in its shell and fleeing. We examined the following two hypotheses using the hermit crab Pagurus filholi : (1) hermit crabs change their preference for shell types that they take refuge in and/or change the timing of fleeing (i.e. the duration of refuge in the shell) when they perceive a predator threat; (2) the type of shell that a hermit crab occupies affects the fleeing tactic of the individual. Under the stimulus of a crushed conspecific, hermit crabs changed neither their preference for shell species nor their refuge duration. On the other hand, under the stimulus of the predatory crab Gaetice depressus , hermit crabs increased their preference for Batillaria cumingi shells, which provide superior protection against predators, and shortened their refuge duration in the shells even when they occupied those effective against predation. Refuge duration was longer in B. cumingi shells than in the more vulnerable shells of Homalopoma sangarense . These results suggest that both antipredator defences (changing shell and timing of fleeing) are induced by the stimulus of a predator, and the timing of fleeing is affected by the shell type occupied.     

X-ray diffraction demonstrates that phosphatidyldiacylglycerol and phosphatidylcholesterol are not lamellar above the main transition temperature

X-ray diffraction was used to investigate the lattice structure of aqueous dispersions of two phosphatidyldiacylglycerols and of a phosphatidylcholesterol above and below the chain melting transition temperature. Previously, Noggle et al. (Biochim. Biophys. Acta (1982) 691, 240-248) had investigated these lipids and had concluded on the basis of electron microscopy that the lipids were in a lamellar state above the transition temperature. However, they found the 31P-NMR signals were not characteristic of lamellar phases. It was, therefore, concluded that these lipids were yielding unexpected 31P-NMR spectra. The present X-ray results demonstrate that, in fact, the lipids are not in a lamellar state above the transition temperature and that the 31P-NMR and X-ray data are not necessarily in disagreement. Characteristics of the phases both above and below the chain melt temperature are discussed.     

The effects of exposure and predation on the shell of two British winkles

Changes in shell size and shell shape of the two British winkles Littorina nigrolineata and L. rudis were studied in relation to exposure and to crab-size. In both species, shells from exposed shores are smaller and more globose than those from sheltered shores. Also, in rudis of exposed shores the mouth is relatively wider. In shores of equally sheltered conditions, shells are bigger at those localities where crabs are large than at those localities where they are small. The largest shells are found in those localities where it is extremely sheltered, and the crabs are very large.
It is argued that on exposed shores, small shells are favoured because they have more possibilities than large ones to shelter in crevices and in barnacle interspaces, from the impact of winds and waves. A globose shell could accommodate more foot muscle and thus enable a stronger adherence to the rock; and an increased mouth diameter would increase the area of foot adherence to the rock. On sheltered shores, on the other hand, large, narrow-mouthed shells are favoured because they discourage crab predation, large crabs being abundant mainly on sheltered shores.
The possible significance of shell size and shape in relation to zonation is discussed, in view of the different predatory and physical conditions which prevail in different zones of the shore, and the different shell specializations which these conditions would require.