A computational framework for the morpho-elastic development of molluskan shells by surface and volume growth

Mollusk shells are an ideal model system for understanding the morpho-elastic basis of morphological evolution of invertebrates' exoskeletons. During the formation of the shell, the mantle tissue secretes proteins and minerals that calcify to form a new incremental layer of the exoskeleton. Most of the existing literature on the morphology of mollusks is descriptive. The mathematical understanding of the underlying coupling between pre-existing shell morphology, de novo surface deposition and morpho-elastic volume growth is at a nascent stage, primarily limited to reduced geometric representations. Here, we propose a general, three-dimensional computational framework coupling pre-existing morphology, incremental surface growth by accretion, and morpho-elastic volume growth. We exercise this framework by applying it to explain the stepwise morphogenesis of seashells during growth: new material surfaces are laid down by accretive growth on the mantle whose form is determined by its morpho-elastic growth. Calcification of the newest surfaces extends the shell as well as creates a new scaffold that constrains the next growth step. We study the effects of surface and volumetric growth rates, and of previously deposited shell geometries on the resulting modes of mantle deformation, and therefore of the developing shell's morphology. Connections are made to a range of complex shells ornamentations.Comment: Main article is 20 pages long with 15 figures. Supplementary material is 4 pages long with 6 figures and 6 attached movies. To be published in PLOS Computational Biolog

Mechanical basis of morphogenesis and convergent evolution of spiny seashells

Convergent evolution is a phenomenon whereby similar traits evolved independently in not closely related species, and is often interpreted in functional terms. Spines in mollusk seashells are classically interpreted as having repeatedly evolved as a defense in response to shell-crushing predators. Here we consider the morphogenetic process that shapes these structures and underlies their repeated emergence. We develop a mathematical model for spine morphogenesis based on the mechanical interaction between the secreting mantle edge and the calcified shell edge to which the mantle adheres during shell growth. It is demonstrated that a large diversity of spine structures can be accounted for through small variations in control parameters of this natural mechanical process. This physical mechanism suggests that convergent evolution of spines can be understood through a generic morphogenetic process, and provides unique perspectives in understanding the phenotypic evolution of this second largest phylum in the animal kingdom.\ud \ud Homoplasy, the appearance of similar traits in separate evolutionary lineages as a result of convergence, parallelism, or evolutionary reversals, is a major concern in phylogenetic analysis for which it is viewed as noise. However, over the past two decades, homoplasy has also become a subject of increasing interest, stimulated by the rise of evolutionary developmental biology (evo devo) and the wish to uncover the developmental basis of this phenomenon (1⇓–3). Spines constitute the most prominent ornamentation of mollusk shells and have evolved in many distantly related fossil and current mollusk species (at least 55 genera and 21 families of current gastropods; 10 genera and 8 families of current bivalves; 11 genera and 8 families of ammonoids; and 6 fossil nautiloid genera; see Fig. 1 for examples). Convergent evolution of spines in mollusks has been addressed in functional terms, these structures being interpreted as having evolved as a defense in response to shell-crushing predators (4⇓–6). This hypothesis is itself the basis of the widely cited “escalation hypothesis,” according to which long-term trends in the fossil record were caused by the evolutionary response of prey to predation pressure (7). The idea that convergent evolution of similar mollusk ornamentations might be fully explained in functional terms is based on the premise that similar characters, perceived as well designed for a presumed function, cannot conceivably have independently evolved fortuitously. Therefore, natural selection is thought to have repeatedly shaped similar functional traits out of random variations

Effect of hot calendering on physical properties and water vapor transfer resistance of bacterial cellulose films

This work investigates the effect of hot calendering on bacterial cellulose (BC) films properties, aiming the achievement of good transparency and barrier property. A comparison was made using vegetal cellulose (VC) films on a similar basis weight of around 40 g.m-2. The optical-structural, mechanical and barrier property of BC films were studied and compared with those of highly beaten VC films. The Youngs moduli and tensile index of the BC films are much higher than those obtained for VC (14.5 16.2 GPa vs 10.8 8.7 GPa and 146.7 64.8 N.m.g-1 vs 82.8 40.5 N.m.g-1), respectively. Calendering increased significantly the transparency of BC films from 53.0 % to 73.0 %. The effect of BC ozonation was also studied. Oxidation with ozone somewhat enhanced the brightness and transparency of the BC films, but at the expenses of slightly lower mechanical properties. BC films exhibited a low water vapor transfer rate, when compared to VC films and this property decreased by around 70 % following calendering, for all films tested. These results show that calendering could be used as a process to obtain films suitable for food packaging applications, where transparency, good mechanical performance and barrier properties are important. The BC films obtained herein are valuable products that could be a good alternative to the highly used plastics in this industry.The authors thank FCT (Fundação para a Ciência e Tecnologia) and FEDER (Fundo Europeu de Desenvolvimento Regional) for the financial support of the project FCT PTDC/AGR-FOR/3090/2012— FCOMP-01-0124-FEDER-027948 and the awarding of a research grant for Vera Costa

The physical basis of mollusk shell chiral coiling

International audienceA theoretical model suggests that a mechanically induced twist of the soft body underlies the formation of helicospiral shells in snails and ammonites and also accounts for the startling and unique meandering shells observed in certain species. This theory addresses fundamental developmental issues of chirality and symmetry breaking: in the case of ammonites, how a bilaterally symmetric body can sometimes secrete a nonsymmetric shell; for gastropods, how an intrinsic twist possibly due to the asymmetric development of musculature can provide a mechanical motor for generating a chiral shell. Our model highlights the importance of physical forces in biological development and sheds light on shell coiling in snails, which have been used for a century as model organisms in genetic research

Mechanical growth and morphogenesis of seashells

Seashells grow through the local deposition of mass along the aperture. Many mathematical descriptions of the shapes of shells have been provided over the years, and the basic logarithmic coiling seen in mollusks can be simulated with few parameters. However, the developmental mechanisms underlying shell coiling are largely not understood and the ubiquitous presence of ornamentation such as ribs, tubercles, or spines presents yet another level of difficulty. Here we develop a general model for shell growth based entirely on the local geometry and mechanics of the aperture and mantle. This local description enables us to efficiently describe both arbitrary growth velocities and the evolution of the shell aperture itself. We demonstrate how most shells can be simulated within this framework. We then turn to the mechanics underlying the shell morphogenesis, and develop models for the evolution of the aperture. We demonstrate that the elastic response of the mantle during shell deposition provides a natural mechanism for the formation of three-dimensional ornamentation in shells

Mechanics unlocks the morphogenetic puzzle of interlocking bivalved shells

International audienceA striking feature in bivalved seashells is that the 2 valves fit together perfectly when closed. This trait has evolved in 2 phyla from a common shell-less ancestor and has been described for hundreds of years. While its functional advantage is clear, there is no understanding of how this feature is generated. A mathematical model of the shell growth process explains how geometry and mechanics conspire to generate an interlocking pattern. This model provides a physical explanation for a prominent example of convergent evolution. By showing how variations in the mechanism create a wide variety of morphological trends the model provides insight into how biophysical processes, probably modulated by genetic factors, are manifest across scales to produce a predictable pattern

Contribution à l'étude de la chimie précombustionnelle d'huiles végétales-carburants. Convention ADEME n.95 75 31. Rapport intermédiaire : préparation des échantillons

Pour mettre en évidence une relation entre la composition chimique des huiles et leur comportement en tant que biocarburant, on recherche l'influence des constituants majoritaires, les triglycérides (coprah, palme et colza) et des constituants mineurs (acides gras libres, diglycérides et phospholipides). On effectue des expériences sur moteur au banc d'essai et hors moteur. On étudiera aussi la composition de la phase gazeuse avant l'inflammation du mélange pour faire le lien entre le délai d'inflammation et la présence ou non de certains composés chimiques résultant des réactions de pyrolyse et/ou d'oxydation des carburants lors de l'injection dans la chambre de combustion. La chimie précombustionnell e est nécessaire à la connaissance du comportement des huiles végétales et de leurs dérivés. Ce rapport présente la préparation des différents échantillons de biocarburants, selon des protocoles expérimentaux mis au point par l'équipe du CIRAD-CP : purification des huiles végétales, préparation des constituants minoritaires et préparation d'un lot d'esters méthyliques de colza purifiés. La composition des biocarburants modèles ainsi que les essais prévus en collaboration avec les chercheurs américains sont présenté

Contribution à l'étude de la chimie précombustionnelle de carburants dérivés d'huiles végétales. Convention ADEME n. 95 75 31. Rapport final

Afin de mettre en évidence une relation entre la composition chimique des huiles et leur comportement en tant que biocarburant, on a recherché l'influence de la composition des constituants majoritaires, les triglycérides (coprah, palme et colza) et l'influence de constituants mineurs (acides gras libres, diglycérides et phospholipides). Des expériences sur moteur au banc d'essai et hors moteur ont été effectuées afin de caractériser le comportement en tant que carburant des produits étudiés. Pour compléter ce travail, on a étudié la composition de la phase gazeuse avant l'inflammation du mélange pour faire le lien entre le délai d'inflammation et la présence ou non de certains composés chimiques résultant des réactions de pyrolyse et/ou d'oxydation des carburants, qui se produisent durant l'injection dans la chambre de combustion. L'étude de la chimie précombustionnelle est donc une étape nécessaire à la connaissance du comportement des huiles végétales et de leurs dérivés en tant que biocarburant. Le premier chapitre présente les biocarburants modèles utilisés, le second et le troisième sont consacrés respectivement à la détermination du délai d'inflammation dans une chambre de combustion à volume constant et à la chimie précombustionnell