Estimation of metapopulation colonization rates from disturbance history and occurrence-pattern data.

Occurrence patterns of many sessile species in dynamic landscapes are not in equilibrium due to their slow rates of metapopulation colonization and extinction. Colonization-extinction data enable the estimation of colonization rates for such species, but collecting the necessary data may require long waiting times between sampling years. Methods for estimating colonization rates of nonequilibrium metapopulations from single occurrence-pattern data have so far relied on additional data on patch ages and on past patch connectivities. We present an approach where metapopulation colonization rates are estimated from occurrence-pattern data and from disturbance history data that inform of past patch dynamics and that can be collected together with occurrence-pattern data. We estimated parameter values regulating patch and metapopulation dynamics by simulating patch network and metapopulation histories that result in present-like patch network configurations and metapopulation occurrence patterns. We tested our approach using occurrence-pattern data of the epiphytic lichen Lobaria pulmonaria in Fennoscandian forests, and fire-scar data that inform of the 400-yr history of fires and host tree dynamics in the same landscapes. The estimated model parameters were similar to estimates obtained using colonization-extinction data. The projected L. pulmonaria occupancy into the future also agreed with the respective projections that were made using the model estimated from colonization-extinction data. Our approach accelerates the estimation of metapopulation colonization rates for sessile species that are not in metapopulation equilibrium with the current landscape structure.

Ab initio study of single-crystalline and polycrystalline elastic properties of Mg-substituted calcite crystals.

We employ ab initio calculations and investigate the single-crystalline elastic properties of (Ca,Mg)CO3 crystals covering the whole range of concentrations from pure calcite CaCO3 to pure magnesite MgCO3. Studying different distributions of Ca and Mg atoms within 30-atom supercells, our theoretical results show that the energetically most favorable configurations are characterized by elastic constants that nearly monotonously increase with the Mg content. Based on the first principles-derived single-crystalline elastic anisotropy, the integral elastic response of (Ca,Mg)CO3 polycrystals is determined employing a mean-field self-consistent homogenization method. As in case of single-crystalline elastic properties, the computed polycrystalline elastic parameters sensitively depend on the chemical composition and show a significant stiffening impact of Mg atoms on calcite crystals in agreement with the experimental findings. Our analysis also shows that it is not advantageous to use a higher-scale two-phase mix of stoichiometric calcite and magnesite instead of substituting Ca atoms by Mg ones on the atomic scale. Such two-phase composites are not significantly thermodynamically favorable and do not provide any strong additional stiffening effect.

Robustness and optimal use of design principles of arthropod exoskeletons studied by ab initio-based multiscale simulations.

Recently, we proposed a hierarchical model for the elastic properties of mineralized lobster cuticle using (i) ab initio calculations for the chitin properties and (ii) hierarchical homogenization performed in a bottom-up order through all length scales. It has been found that the cuticle possesses nearly extremal, excellent mechanical properties in terms of stiffness that strongly depend on the overall mineral content and the specific microstructure of the mineral-protein matrix. In this study, we investigated how the overall cuticle properties changed when there are significant variations in the properties of the constituents (chitin, amorphous calcium carbonate (ACC), proteins), and the volume fractions of key structural elements such as chitin-protein fibers. It was found that the cuticle performance is very robust with respect to variations in the elastic properties of chitin and fiber proteins at a lower hierarchy level. At higher structural levels, variations of design parameters such as the volume fraction of the chitin-protein fibers have a significant influence on the cuticle performance. Furthermore, we observed that among the possible variations in the cuticle ingredients and volume fractions, the experimental data reflect an optimal use of the structural variations regarding the best possible performance for a given composition due to the smart hierarchical organization of the cuticle design.

Influence of microstructure on deformation anisotropy of mineralized cuticle from the lobster Homarus americanus.

The exoskeleton of the American lobster Homarus americanus is a hierarchically organized nano-composite material consisting of organic chitin-protein fibers associated with inorganic calcium carbonate. The presence of a well-developed and periodically arranged pore canal system leads to a honeycomb-like structure. The concomitant presence of the twisted plywood arrangement of the mineralized chitin-protein fibers alters the elastic properties, the deformation behavior, and fracture behavior compared to classical honeycomb structures. By performing compression tests in various directions of the cuticle we examined the anisotropic elastic-plastic deformation and fracture behavior of mineralized parts of the exoskeleton. By applying digital image correlation during compression testing, the evolution of the elastic-plastic deformation at the microscopic scale was observed with high resolution and simultaneously global stress and strain data were acquired. Shear tests were performed in order to determine the fracture energy for different shear planes and directions. The investigation of the microstructure after plastic deformation revealed the underlying deformation mechanisms of lobster endocuticle from the claws under different loading conditions. For evaluating the effect of hydration the samples were tested both in the dry and in the wet state.

Preferred crystallographic texture of alpha-chitin as a microscopic and macroscopic design principle of the exoskeleton of the lobster Homarus americanus.

The crystallographic texture of the crystalline alpha-chitin matrix in the biological composite material forming the exoskeleton of the lobster Homarus americanus has been determined using synchrotron X-ray pole figure measurements and the calculation of orientation distribution functions. The study has two objectives. The first one is to elucidate crystallographic building principles via the preferred synthesis of certain orientations in crystalline organic tissue. The second one is to study whether a general global design principle exists for the exoskeleton which uses preferred textures relative to the local coordinate system throughout the lobster cuticle. The first point, hence, pursues the question of the extent to which and why alpha-chitin reveals preferred textures in the lobster cuticle. The second point addresses the question of why and whether such preferred textures (and the resulting anisotropy) exist everywhere in the exoskeleton. Concerning the first aspect, a strong preference of a fiber texture of the orthorhombic alpha-chitin is observed which is characterized by a 020 crystal axis normal to the exoskeleton surface for the chitin matrix. The second question is tackled by studying samples from different parts of the carapace. While the first aspect takes a microscopic perspective at the basic structure of the biological composite, the second point aims at building a bridge between an understanding of the microstructure and the macroscopic nature of a larger biological construction. We observe that the texture is everywhere in the carapace optimized in such a way that the same crystallographic axis of the chitin matrix is parallel to the normal to the local tangent plane of the carapace. Notable differences in the texture are observed between hard mineralized parts on the one hand and soft membranous parts on the other. The study shows that the complex hierarchical microstructure of the arthropod cuticle can be well described by surprisingly simple crystallographic textures.

Experimental investigation of the elastic-plastic deformation of mineralized lobster cuticle by digital image correlation.

This study presents a novel experimental approach to the characterization of the deformation of a mineralized biological composite using arthropod cuticle as a model material. By performing tensile tests combined with a detailed strain analysis via digital image correlation, the elastic-plastic deformation behavior of the endocuticle of the American lobster Homarus americanus is examined. The test specimens originate from the pincher and crusher claws. For evaluating the effect of moisture on the deformation behavior, the samples are tested both in dry and in wet state. Sample characterization using the digital image correlation method requires a stochastic spot pattern on the sample surface. Digital images are then taken at subsequent deformation stages during the mechanical test. These images are used to calculate the displacement, the displacement gradient, and the strain fields via pattern correlation. The method is applied both, at a global scale to measure with high precision the stress-strain behavior of the bulk cuticle and at a microscopic scale to reveal strain heterogeneity, strain patterning, and strain localization phenomena.

[Clinical and hematological profile of hemoglobin C Ziguinchor (Cz) in Western Africa]. / Profil clinique et hématologique de l'hémoglobine C Ziguinchor (Cz) en Afrique Occidentale.

The authors report 10 cases of Hb C Ziguinchor share out in 3 features ACz, SCz, Cz-PHHF (HPFH: hereditary persistence of foetal hemoglobin). The clinical and hematological study of the features has allowed the following conclusions: the Hb Cz is a rare mutant specific of the Negro and which original focus may be in Senegal. The heterozygote form (ACz) does not present any clinical manifestation. The association Hb S-Hb Cz brings about a serious hemoglobinopathy which has clinical and hematological features like the sickle cell disease (SS). The association Hb Cz-HPFH is relatively supported in spite of episodic painful crisis.

Prevalence of the sickle cell trait among students in a physical education college in Côte-d'Ivoire.

The prevalence of sickle cell trait (SCT), was studied in 263 students enrolled in a physical education college in Côte-d'Ivoire. Most of the students were athletes of average training level, but some competed at an international level. The prevalence of SCT (hemoglobin AS), observed in the student population (13.7%) was not significantly different from that of the general population (12%) of Côte-d'Ivoire and did not differ between sexes. The percentage of international level athletes was similar in SCT (25%) and control (hemoglobin AA) groups (25.7%). Particular activities practised by SCT international level athletes were individual track events (sprint race, 400 m race and long and high jump) as well as team sports (football and handball), indicating the excellent aptitude for aerobic and anaerobic metabolic activities. As none of the international athletes engaged in endurance activities, no conclusions can be drawn regarding either the aptitude of SCT subjects for intense and prolonged exertion or a possible limitation of oxygen transport produced by their hemoglobinopathy.

[A case of association of Hb C Ziguinchor (alpha A2 beta 6-2 (A3) Glu replaced by Val beta 58 (E2) Pro replaced by Arg) with a hereditary persistence of fetal hemoglobin (HPFH). Clinical and biological results]. / Un cas d'association d'Hb C Ziguinchor (alpha A2 beta 62 (A3) Glu----Val beta 58 (E2) Pro----Arg) avec une persistance hereditaire d'Hb foetale (PHHF).

The authors report on one case of association between Hb C Ziguinchor and an hereditary persistence of Hb foetal. Despite an high rate of Hb F estimated at 37,2% painful manifestations due to Hb S (beta 6 Glu-Val) mutation are present.

Adaptation of electrolyte transport in rat large intestine after proximal resection. I. Cecum and colon after 60% jejunoilectomy.

Electrolyte transport was studied in rat cecum and colon adapting to 60% resection of the small intestine. Four weeks after surgery, the absorbing gross surface area, dry and wet weight, net absorption in vivo of sodium, chloride and volume, net potassium secretion, transmural electrical potential difference and mucosal Na-K-ATPase specific activity were determined. In the cecum, all tissue mass parameters were increased compared to sham-operated controls. Net transport was stimulated per organ but not per unit mass, and potential difference and Na-K-ATPase remained unaffected. In the colon, surface area and wet weight increased slightly while dry weight and electrolyte transport were not influenced. Thus, by enlargement without a change in cell function, the cecum but not the colon contributes to electrolyte homoeostasis after 60% jejunoilectomy in the rat. Na-K-ATPase specific activity and electrical potential difference were higher in the colon than the cecum, suggesting segmental heterogeneity of the larger bowel with respect to Na-K-ATPase-linked active sodium absorption.

[Hematologic profile of hemoglobin "Hope" (beta 136 (H14) Gly-Asp) in the West African]. / Profil hématologique de l'hémoglobine "Hope" (beta 136 (H14) Gly-Asp) dans l'ouest Africain.

Detection of 11 cases of hemoglobin "Hope" after family study in three isolated cases led us to establish an hematologic profile of this hemoglobin. The first observation which can be done is the geographic origin of the propositus. All of these originated from the sub-sahelian zone. The second observation is the discovery of anemia for all carriers of this hemoglobin.

[Rare hemoglobins in Ivory Coast and West Africa]. / Les hémoglobines rares en Côte d'Ivoire et en Afrique occidentale.

Detection of drepanocytosis, which affects 12 p. 100 of the people living in Ivory Coast, is a part of the routine check up performed in hospitals. In 13 years of screening, electrophoresis has been carried out on about 170,000 samples. This work has led the authors to the typing of a certain number of uncommon hemoglobins (277 cases). As the technical methods have been greatly improved over the past few years, it is most likely that new hemoglobin mutants will continue to be discovered. A special interest of their typing consists in the fact these hemoglobins seem to be found either within specific areas or in special ethnic groups.

[Clinical hematological and biochemical pattern of three SN Baltimore hemoglobin carriers (author's transl)]. / Profil clinique, hématologique et biochimique de trois proteurs d'hémoglobine SN Baltimore (alpha alpha beta 6 beta 95 GLU).

The clinical, hematologic and biochemical study of three children, carriers of the double heterozygotous SN Baltimore hemoglobin from Guadeloupe, have not allowed to detect any typical anomaly and specially no sign of anemia or hemolysis. An iron deficiency of parasitologic origin has only been detected. This absence of pathological symptoms is related to the fact that SN red cells tend to sickle less rapidly than those from persons with sickle cell trait AS.

[Polymorphism of hemoglobins D in Ivory Coast: Hb Korle Bu (beta 73 (E17) Asp leads to Asn), Hb Avicenna (beta 47 (CD6) Asp leads to Ala) and Hb Cocody (beta 21 (B3) Asp leads to Asn) (author's transl)]. / Polymorphisme des hémoglobines D en Côte-d'Ivoire : hémoglobine Korle Bu (bêta 73 (E17) Asp leads to Asn), hémoglobine Avicenna (bêta 47 (CD6) Asp leads to Ala) et hémoglobine Cocody (bêta 21 (B3) Asp leads to Asn).

A recent screening performed at the CHU Cocody in Abidjan (Ivory Coast) revealed six cases of hemoglobin "D". The use of a rapid strategy based on isoelectric focusing studies, finger-printing, reverse phase high performance liquid chromatography and solid phase microsequence technique led to the characterization of three abdominal hemoglobins. The first variant corresponded to the Hb Korle Bu (beta 73 (E17) Asp leads to Asn) (pI = 7.210) which is common in this country. The second, Hb Avicenna (beta 47 (CD6) Asp leads to Ala) (pI = 7.225) has not yet been reported in Africa. The last one was a new variant, Hb Cocody (beta 21 (B3) Asp leads to Asn) (pI = 7.205). A large number of hemoglobin "D" have been detected in European, American negroes, Amerindian or Asiatic populations, but only few observations were reported in Africa. Large screenings and discriminative methodologists must provide information on the polymorphism of hemoglobin D in the African population.

[Rare hemoglobins in Guadeloupe and in the Lesser Antilles (author's transl)]. / Hémoglobines rares en Guadeloupe et aux Petites Antilles.

Screening of abnormal hemoglobins on 25 136 samples allowed us to detect from 1974-1979 rare or uncommon hemoglobins as N Baltimore, Korle Bu, Lepore, K Woolwich, J Broussais and J Baltimore. Hemoglobins N Baltimore, J Broussais, and J Baltimore are detected for the first time in Guadedoupe. The identification of these asymptomatic hemoglobins in this part of the Carribbean region provides information concerning the exact origin of the black population of these islands; e.g., hemoglobin K Woolwich and N Baltimore are found only in specific regions of West Africa.

[Hemoglobin N Baltimore: 28 cases in one Guadeloupe family (author's transl)]. / 28 cas d'hémoglobine N Baltimore dans une famile guadeloupéenne.

The detection of hemoglobin AN Baltimore in a young man, 28 years old in June 1978, led us make a family study. This family study was very interesting because our proband had 16 brothers and sisters, many of whom also had many children. Research on abnormal hemoglobins was done on 46 family members: 28 were carriers of hemoglobin AN Baltimore and three children, carriers of heterozygote SN Baltimore.