Effects of lithium and potassium on recovery of solute uptake capacity of Acer pseudoplatanus cells after gas-shock

At concentrations of 10-^?3M, Li⁺ inhibits the recovery of solute uptake capacity of Acer pseudoplatanus L. cell suspension cultures after gas-shock (i.e. after rapid exchange of the atmosphere in the culture flasks for ambient air). It also reduces solute uptake capacity of cells having already attained high rates of uptake during recovery from gas-shock. The effects of Li⁺ are much greater in cells which have been cultivated in 7 mM K⁺ solution than in cells cultivated with higher K⁺ levels (19 mM). Increasing K⁺ concentration during recovery reverses the effect of 10^–3M Li⁺ and, with sufficiently high concentrations of K⁺ (≥ 10-^?2M) during recovery, the solute uptake capacity of the fully recovered cells can even become greater than that of the control, at least for the low values of substrate concentration (here sulphate 10-^?5M). Since Li⁺ does not affect the time course of solute uptake measured over 15–20 min, it is thought that it interacts with the synthesis and turnover of the solute uptake machinery of the Acer pseudoplatanus cells. Thermodynamic analysis of the flux data also supports the hypothesis that Li⁺ inhibits the biosynthesis of specific sites of solute permeation, but it does not rule out the possibility that K⁺ interferes rather on the forces acting on the transport of the considered solutes than on the catalytic structures of permeation.     

Cytoplasmic Influence on Lethality in Nucleocytoplasmic and Natural Hybrids between Bufo Calamita Laur and Bufo Bufo L. (Amphibia, Anura)

Nucleocytoplasmic interactions have been studied through nuclear and cytoplasmic grafts. Bufo bufo nuclei transplanted in Bufo calamita eggs provoked 95% lethality during gastrulation. Influence of the cytoplasm in such a nucleocytoplasmic incompatibility has been studied through cytoplasmic fractionation and grafting of the fractions obtained. Fractionation of egg cytoplasm gave three fundamental fractions: lipid, hyaline cytoplasm and vitellus. After injection of B. calamita fractions into B. bufo fertilized eggs, the hyaline cytoplasmic fraction provoked a gastrulation block in the same ratio (95%) as in the interspecific nuclear graft experiment. Influence of the hyaline cytoplasmic fractions of both species has been tested on nucleocytoplasmic and natural hybrid developments. The B. calamita hyaline cytoplasmic fraction provoked in each case a developmental block at the beginning of gastrulation. The B. bufo hyaline cytoplasmic fraction acts later at the yolk plug stage and in some cases partially corrects the developmental bolck or exogastrulation of young hybrid gastrula. It can be generalized that in both kinds of hybrids, the hyaline cytoplasmic fraction of B. calamita exerted a lethal effect on B. bufo nucleus.     

Phylogenetic signal in bone histology of amniotes revisited

Legendre, L, Le Roy, N, Martinez‐Maza, C, Montes, L, Laurin, M & Cubo, J. (2012). Phylogenetic signal in bone histology of amniotes revisited. —Zoologica Scripta, 42, 44–53. There is currently a debate about the presence of a phylogenetic signal in bone histological data, but very few rigorous tests have fuelled the discussions on this topic. Here, we performed new analyses using a larger set of seven histological traits and including 25 taxa (nine extinct and 16 extant taxa), using three methods: the phylogenetic eigenvector regression, the tree length distribution and the regressions on distance matrices. Our results clearly show that the phylogenetic signal in our sample of bone histological characters is strong, even after correcting for multiple testing. Most characters exhibit a significant phylogenetic signal according to at least one of our three tests, with the phylogeny often explaining 20–60% of the variation in the histological characters. Thus, we conclude that the phylogenetic comparative method should be systematically used in interspecific analyses of bone histodiversity to avoid problems of non‐independence among observations.     

House mouse dispersal in Iron Age Spain: a geometric morphometrics appraisal

During the Iron Age, sea trade in the Mediterranean increased, particularly with the expansion of Phoenician and Greek colonies in the Western Mediterranean. A side effect of these human movements was the involuntary dispersion of commensal species, such as the house mouse (Mus musculus domesticus). One archaeological layer dated from the 4th Century BC, coming from an Iberian village located in the Mediterranean coast of Spain, contained a large and reliable accumulation of small mammals. The presence of the house mouse was highly suspected within this layer. To assess its abundance quantitatively, we used a geometric morphometrics approach of the first lower molar contour using elliptical Fourier analysis. We also increased the power of the discrimination between the Algerian mouse (Mus spretus) and the house mouse by combining a dimension reduction approach together with different validation procedures. The relative importance of age, sex, and geographical origin onto the shape and form of the lower molar contour was also investigated. The results obtained demonstrate the presence and the dominance of the house mouse in the landscape surrounding the Iberian village in the 1st Millennium BC, only a few centuries after its arrival in the Western Mediterranean Basin. A cross‐validated linear discriminant function considering different Mediterranean populations suggest Morocco and France as the most probable geographical origins for the Algerian mouse, and Tunisia for the origin of house mice in North‐Eastern Spain. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 483–497.     

Combining geometric morphometrics with pattern recognition for the investigation of species complexes

The parasitoid Hymenoptera contain a large number of species complexes that are as yet unresolved by traditional taxonomic studies. Evolutionary studies as well as biological control programmes often require further investigations which cannot rely on simple qualitative morphological characters; in many cases, particularly with dried specimens housed in museums, molecular approaches cannot be used. Recent developments in geometric morphometrics and statistical exploratory approaches open new perspectives for the objective evaluation of morphological characters in this taxonomic context. In this study, geometric morphometrics and pattern recognition approaches were applied to the wing shape and venation of two closely related braconid species considered to differ by subtle qualitative morphological head characters. Exploratory analyses such as kernel density estimates and Gaussian mixture analyses were used to explore the structure of the data in the multivariate morphometric space. Discrimination techniques (linear discriminant functions and neural networks combined with cross‐validations) were used to estimate the taxonomic value of qualitative characters. Gaussian mixtures highlighted the existence of two non‐overlapping groups. A good congruence was found between one of the two groups and the a priori defined Bassus tumidulus. The misclassification rate was higher for B. tegularis specimens, which also appeared morphometrically heterogeneous. Discrimination between the two a priori defined species was incomplete with misclassification rates higher than, or equal to, 6%. In most cases, the lack of congruence between species and morphometrically defined subgroups could be related to specimens that exhibited ambiguous qualitative character states. In summary, if two entities are present, they still need to be defined morphologically, while B. tegularis heterogeneity calls for further investigation of specimens of known origin and hosts. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 89–98.     

A Freeze-Fracture Study of the Cortex of Xenopus laevis Eggs

The organization of the cortex of Xenopus laevis eggs was investigated by freeze-fracture electron microscopy. The cortical endoplasmic reticulum (CER) formed a network surrounding and interconnecting the cortical granules. It formed junctions with the plasma membrane and was confluent with the ER in subcortical regions. Intramembranous particles (IMP₁) were only present in the P face of the CER, the E face being apparently devoid of pits and particles. Arrays of densely packed IMP₁, having a mean diameter of 17 nm, were restricted to the microvillar region of the plasma membrane. The cortical granule membrane also contained IMP₁ (mean diameter, 21 nm) that were sparsely and randomly distributed. Several types of cortical granule seemed to exist based on an analysis of the distribution of the different IMP sizes.