Humoral Recognition Factors in the Arthropoda. The Specificity of Chelicerata Serum Lectins

Arthropods have the capacity of recognizing self from non-selfin various defense phenomena including hemolymph clotting, phagocytosis,encapsulation, melanization and clearance of the foreign matterwhich must be initiated by a first step of molecular recognition."Natural" and experimentally induced humoral factors have beendescribed which act as hemagglutinins, bacterial agglutinins,precipitins, bactericidal factors, bacteriolysins, hemolysins,opsonins, clotting factors, and lysozymes. Their exact rolein recognition functions has not been fully explored and theirfunction remains unclear. Among these factors, the carbohydrate-bindingmolecules (lectins) are the best characterized in their specificity,physicochemical properties and molecular structure. Arthropodlectins are multimeric, high molecular weight protein (glycoprotein)molecules with a certain degree of heterogeneity in their specificityand structure. In particular, serum lectins from chelicerates(horseshoe crabs, scorpions and spiders) share a common property:the specificity for sialic acids. Arachnids and merostomes divergedin the earliest Cambrian. Since they occupy markedly differenthabitats, the sialic acid specific lectins most probably area relict rather than an adaptative character. In addition tothis common feature of specificity, lectins from cheliceratesand other arthropods represent heterogeneous populations whichcan bind a wide variety of carbohydrates, many of them presenton bacteria as D-galactose, 2-keto-3-deoxyoctonate, glucuronicacid, N-acetylmuramic acid, and colominic acid. Multiplicityin specificity suggests that serum lectins might contributeas a carbohydrate-based recognition system for the non-self.The requirement for avoiding self recognition would be thatcarbohydrate structures potentially recognized by the systemwould be absent, masked or out of reach of this humoral factoror cell associated recognition factors.     

Development and Structure of Phloem in the Petiole of Lagenaria siceraria (Mol.) Standl. and Momordica charantia L.

Light microscopic studies of the petioles of Lagenaria sicerariareveal that the external phloem of each bicollateral vascularbundle develops earlier than the internal phloem, and that thesieve elements of the external phloem are arranged in the outerand inner zones. Each sieve element of L. siceraria and Momordicacharantia is vertically associated with a maximum of six andtwo companion cells respectively. Discrete granular bodies seenin the cytoplasm of young sieve elements develop into globular,oval, or elongated slime bodies. Enlargement and fusion of slimebodies, and the subsequent dispersal of slime occur in the parietalcytoplasm. The dispersal of slime coincides with degradationof the nucleus and perforation of the pore sites. Before nucleardisorganization, the sieve-element nucleolus is extruded. Slimeafter its immediate dispersal appears amorphous and uniformlydistributed in the sieve elements. Plugs exhibit varying degreesof condensation of slime near the sieve plates. Certain maturesieve elements in the external phloem of L. siceraria have ovalbodies which we consider reaggregated or undispersed slime.Evidence has been obtained that a central cavity occurs in afew, almost mature, sieve elements wherein the cytoplasm includingthe slime is peripheral.     

Some Digenetic Trematodes of Marine Fishes from Israel's Mediterranean Coast and Their Zoogeography, Especially Those from Red Sea Immigrant Fishes

A total of 500 fishes (59 species) from Israel's Mediterranean coastal waters were examined for digenetic trematodes and 201 (40.2%) harbored at least one species. One new genus (Propar-vipyrum) and 11 new species are described: Bacciger israelensis (Fellodistomidae) from Sarpa salpa and Boops boops; Ancylocoelium israelense and Chrisomon israelensis (both Monor-chiidae) from Atule djeddaba; Diphtherostomum israelense (Zoogonidae) from Diplodus sargus, D. vulgaris and Saurida undosquamis; Proparvipyrum israelense (Zoogonidae) from Mullus surmuletus; Acanthocolpoides israelensis (Lepocreadiidae) from Sardinella maderen-sis; Neolepidapedon israelense (Lepocreadiidae) from Mullus surmuletus; Podocotyle jaffen-sis (Opecoelidae) from Denlex filosus; Podocotyle (Pedunculotrema) israelensis frqm Pomadasys incisus and Pelates quadrilineatus; Lecithochirium haifense (Hemiuridae) from Atule djeddaba; Lecithochirium israelense from Trachinus araneus and Scyris alexandrina. 36 previously known species were identified, and all represent new geographical distribution records. Some Red Sea immigrant fishes brought trematodes with them to the Mediterranean and some acquired Atlanto-Mediterranean species.     

Biodiversity in microbial communities: system scale patterns and mechanisms

The relationship between anthropogenic impact and the maintenance of biodiversity is a fundamental question in ecology. The emphasis on the organizational level of biodiversity responsible for ecosystem processes is shifting from a species-centred focus to include genotypic diversity. The relationship between biodiversity measures at these two scales remains largely unknown. By stratifying anthropogenic effects between scales of biodiversity of bacterial communities, we show a statistically significant difference in diversity based on taxonomic scale. Communities with intermediate species richness show high genotypic diversity while speciose and species-poor communities do not. We propose that in species-poor communities, generally comprising stable yet harsh conditions, physiological tolerance and competitive trade-offs limit both the number of species that occur and the loss of genotypes due to decreases in already constrained fitness. In species-rich communities, natural environmental conditions result in well-defined community structure and resource partitioning. Disturbance of these communities disrupts niche space, resulting in lower genotypic diversity despite the maintenance of species diversity. Our work provides a model to inform future research about relationships between species and genotypic biodiversity based on determining the biodiversity consequences of changing environmental context.     

Structural and functional investigation of a secreted chorismate mutase from the plant-parasitic nematode Heterodera schachtii in the context of related enzymes from diverse origins

In this article, we present the cloning of Hscm1 , a gene for chorismate mutase (CM) from the beet cyst nematode Heterodera schachtii . CM is a key branch-point enzyme of the shikimate pathway, and secondary metabolites that arise from this pathway control developmental programmes and defence responses of the plant. By manipulating the plant's endogenous shikimate pathway, the nematode can influence the plant physiology for its own benefit. Hscm1 is a member of the CM gene family and is expressed during the pre-parasitic and parasitic stages of the nematode's life cycle. In situ mRNA hybridization reveals an expression pattern specific to the subventral and dorsal pharyngeal glands. The predicted protein has a signal peptide for secretion in addition to two domains. The N-terminal domain of the mature protein, which is only found in cyst nematodes, contains six conserved cysteine residues, which may reflect the importance of disulphide bond formation for protein stabilization. The C-terminal domain holds a single catalytic site and has similarity to secreted CMs of pathogenic bacteria, classifying HsCM1 as an AroQ_γ enzyme. The presumed catalytic residues are discussed in detail, and genetic complementation experiments indicate that the C-terminal domain is essential for enzyme activity. Finally, we show how the modular design of the protein is mirrored in the genomic sequence by the intron/exon organization, suggesting exon shuffling as a mechanism for the evolutionary assembly of this protein.     

Fat frogs,mobile genes: unexpected phylogeographic patterns for the ornate chorus frog (Pseudacris ornata)

The southeastern coastal plain of the United States is a region marked by extraordinary phylogeographic congruence that is frequently attributed to the changing sea levels that occurred during the glacial‐interglacial cycles of the Pleistocene epoch. A phylogeographic break corresponding to the Apalachicola River has been suggested for many species studied to date that are endemic to this region. Here, we used this pattern of phylogeographic congruence to develop and test explicit hypotheses about the genetic structure in the ornate chorus frog (Pseudacris ornata). Using 1299 bp of mtDNA sequence and seven nuclear microsatellite markers in 13 natural populations of P. ornata, we found three clades corresponding to geographically distinct regions; one spans the Apalachicola River (Southern Clade), one encompasses Georgia and South Carolina (Central Clade) and a third comprises more northerly individuals (Northern Clade). However, it does not appear that typical phylogeographic barriers demarcate these clades. Instead, isolation by distance across the range of the entire species explained the pattern of genetic variation that we observed. We propose that P. ornata was historically widespread in the southeastern United States, and that a balance between genetic drift and migration was the root of the genetic divergence among populations. Additionally, we investigated fine‐scale patterns of genetic structure and found the spatial scale at which there was significant genetic structure varied among the regions studied. Furthermore, we discuss our results in light of other phylogeographic studies of southeastern coastal plain organisms and in relation to amphibian conservation and management.