Skull osteology and osteological phylogeny of the Western whip snake Hierophis viridiflavus (Squamata,Colubridae)

The skull osteology of Hierophis viridiflavus is here described and figured in detail on the basis of 18 specimens. The sample includes specimens from the ranges of both H. viridiflavus viridiflavus and H. viridiflavus carbonarius as well as specimens not identified at sub-specific level. The main characters that define H. viridiflavus in comparison to the parapatric congeneric species Hierophis gemonensis are wide maxillary diastema, basioccipital crest well distinct in three lobes and basioccipital process well marked. The foramina of the otoccipital and prootic, and the basioccipital process of the basioccipital are among the most ontogenetically variable characters, as indicated by two juvenile specimens included in the sample. A specimen-level phylogenetic analysis including H. gemonensis and other outgroups (overall 6 species, 26 specimens, 64 skull characters) recovered all H. viridiflavus specimens in one clade, indicating the presence of a clear phylogenetic signal in the applied characters. However, the resolution within the H. viridiflavus clade is poor the monophyly of H. viridiflavus carbonarius was retrieved, but not that of Hierophis v. viridiflavus. Probably due to the relatively high variability, the skull morphology does not support the recently proposed specific status of the two subspecies.     

Developmental phenotypic plasticity: Where ecology and evolution meet molecular biology

The plastic response of phenotypic traits to environmental change is a common research focus in several disciplines - from ecology and evolutionary biology to physiology and molecular genetics. The use of model systems such as the flowering plant Arabidopsis thaliana has facilitated a dialogue between developmental biologists asking how plasticity is controlled (proximate causes) and organismal biologists asking why plasticity exists (ultimate causes). Researchers studying ultimate causes and consequences are increasingly compelled to reject simplistic, ‘black box’ models, while those studying proximate causes and mechanisms are increasingly obliged to subject their interpretations to ecological ‘reality checks.’ We review the successful multidisciplinary efforts to understand the phytochrome-mediated shade-avoidance and light-seeking responses of flowering plants as a pertinent example of convergence between evolutionary and molecular biology. In this example, the two-way exchange between reductionist and holist camps has been essential to rapid and sustained progress. This should serve as a model for future collaborative efforts towards understanding the responses of organisms to their constantly changing environments.     

Identification, sequencing and mutagenesis of the gene for a d-carbamoylase from Agrobacterium radiobacter

Abstract A clone positive for d-carbamoylase activity (2.7 kb Hin dIII- Bam H1 DNA fragment) was obtained by screening a genomic library of Agrobacterium radiobacter in Escherichia coli . This DNA fragment contains an open reading frame of 912 bp which is predicted to encode a peptide of 304 amino acids with a calculated molecular mass of 34247 Da. The d-carbamoylase gene. named cauA , was placed under the control of T7 RNA-dependent promoter and expressed in E. coli BL21 (DE3). After induction with isopropyl-thio-β-d-galactopyranoside, the synthesis of d-carbamoylase in E. coli reached about 40% of the total protein. The expressed protein was shown to possess a molecular mass, on SDS-PAGE, of 36 kDa and showed an enhanced allowed us to establish that a Pro¹⁴→Leu¹⁴ exchange leads to an inactive enzyme species, while a Cys²⁷⁹→Ser²⁷⁹ exchange did not impair the functional properties of the enxyme.     

Feeding and energy budget estimations inDaphnia obtusa

The reproductive and growth strategies ofDaphnia obtusa are discussed in terms of energy budget. The results obtained through feeding and life table experiments allow us to understand the role of biotic factors, such as competition and predation, in the evolution of life history traits.     

Lymphoid precursor cells adhere to two different sites on fibronectin

Several precursor lymphoid cell lines, blocked at specific stages of differentiation, adhere specifically to fibronectin in vitro. Whereas the Ba F3 cell line, which has both immunoglobulin heavy- and light-chain genes in germline configuration, interacts with the arg-gly-asp-containing cell-binding domain of fibronectin, the B-committed line PD 31, which is undergoing rearrangement of immunoglobulin light-chain genes, does not. Accordingly the Ba F3, but not the putative PD 31 surface fibronectin receptor, binds to an affinity matrix containing the 115-kD cell-binding domain of fibronectin. PD 31 cells recognize a different domain of the fibronectin molecule, which is contained within the carboxy terminal segment possessing a high-affinity binding site for heparin. A polyclonal antibody raised against the fibronectin receptor of mouse erythroleukemic cells inhibits adhesion of these lymphoid lines to fibronectin. It precipitates two major species of 140 and 70 kD from surface-radioiodinated Ba F3 cells and species of 140 and 120 kD from PD 31 cells. We propose that the two types of cells express different fibronectin receptors mediating substrate adhesion, and suggest that receptor(s) with different specificity might be expressed in the course of B cell maturation. Because we show that these adhesion properties are shared by normal bone marrow lymphoid precursors, we infer that these receptors may play a role in normal lymphopoiesis.     

Directional fixation of mutations in vertebrate evolution

Summary We have made pairwise comparisons between the coding sequences of 21 genes from coldblooded vertebrates and 41 homologous sequences from warm-blooded vertebrates. In the case of 12 genes, GC levels were higher, especially in third codon positions, in warm-blooded vertebrates compared to cold-blooded vertebrates. Six genes showed no remarkable difference in GC level and three showed a lower level. In the first case, higher GC levels appear to be due to a directional fixation of mutations, presumably under the influence of body temperature (see Bernardi and Bernardi 1986b). These GC-richer genes of warm-blooded vertebrates were located, in all cases studied, in isochores higher in GC than those comprising the homologous genes of cold-blooded vertebrates. In the third case, increases appear to be due to a limited formation of GC-rich isochores which took place in some cold-blooded vertebrates after the divergence of warm-blooded vertebrates. The directional changes in the GC content of coding sequences and the evolutionary conservation of both increased and unchanged GC levels are in keeping with the existence of compositional constraints on the genome.