The role of epiphytism in architecture and evolutionary constraint within mycorrhizal networks of tropical orchids

Characterizing the architecture of bipartite networks is increasingly used as a framework to study biotic interactions within their ecological context and to assess the extent to which evolutionary constraint shape them. Orchid mycorrhizal symbioses are particularly interesting as they are viewed as more beneficial for plants than for fungi, a situation expected to result in an asymmetry of biological constraint. This study addressed the architecture and phylogenetic constraint in these associations in tropical context. We identified a bipartite network including 73 orchid species and 95 taxonomic units of mycorrhizal fungi across the natural habitats of Reunion Island. Unlike some recent evidence for nestedness in mycorrhizal symbioses, we found a highly modular architecture that largely reflected an ecological barrier between epiphytic and terrestrial subnetworks. By testing for phylogenetic signal, the overall signal was stronger for both partners in the epiphytic subnetwork. Moreover, in the subnetwork of epiphytic angraecoid orchids, the signal in orchid phylogeny was stronger than the signal in fungal phylogeny. Epiphytic associations are therefore more conservative and may co‐evolve more than terrestrial ones. We suggest that such tighter phylogenetic specialization may have been driven by stressful life conditions in the epiphytic niches. In addition to paralleling recent insights into mycorrhizal networks, this study furthermore provides support for epiphytism as a major factor affecting ecological assemblage and evolutionary constraint in tropical mycorrhizal symbioses.     

The Administration of an α-MSH Analogue Reduces the Serum Release of IL-1α and TNFα Induced by the Injection of a Sublethal Dose of Lipopolysaccharides in the BALB/c Mouse

The injection of α-MSH or of one of its analogues ([Nle₄-D.Phe₇] α-MSH_4–10) reduced, in vivo, the release of two cytokines (IL-1α and TNFα) involved in inflammation. The inflammatory state was induced in BALB/c mice by intraperitoneal injection of a sublethal dose of lipopolysaccharides (LPS). The assay of these cytokines by ELISA showed a reduction of 20% with α-MSH and between 30 and 60% with the α-MSH analogue. The α-MSH or the analogue was administered in one of two ways: intravenously or subcutaneously. The most efficient method seemed to be the subcutaneous one because it improved the activity 10,000 times more than the intravenous method. Moreover, the analogue induced a regression of mortality in the animals treated by the intravenous method. Our results show that α-MSH and one of its analogues inhibit IL-1α and TNFα, and can be used as anti-inflammatory molecules.     

Examination of the 'founder effect' in biodiversity research: patterns and imbalances in the published literature

We reviewed 2524 articles published from 1987 to 1995 in five international journals, Conservation Biology , Biological Conservation , Biodiversity and Conservation , Ecological Applications , and the Journal of Applied Ecology , to assess patterns and imbalances in biodiversity research in the following subject areas: locations where research was conducted, types of organisms studied, types of ecosystems studied, types of methodologies used, and types of stresses investigated. Biodiversity research was found to be narrowly focused with little deviation from its initial course set of being a discipline concerned largely with the implications of forest habitat loss on charismatic terrestrial megafauna; i.e. the 'founder effect' is very much in evidence. The 'sleeping dragon' of ignored marine biodiversity is really symptomatic of a wider problem, and can perhaps be referred to as a 'hibernating hydra' of many imbalances due to, for example, under-representations of research from developing nations, or on amphibians and invertebrates, alpine and arctic systems, sociological components and chemical stresses etc. It is time to take steps to actively awaken the creature so that conservation biology/applied ecology can become more pluralistic in scope.     

The Combined Effect of Hydrogen Peroxide and Ultraviolet Irradiation on Bacterial Spores

Ultra-violet (u.v.) light irradiation of spores of Bacillus subtilis in the presence of hydrogen peroxide produced a rapid kill which was up to 2000-fold greater than that produced by irradiation alone. A kill of 99–99% was produced by 30s u.v. irradiation of spores of 6 strains of Bacillus and Clostridium in the presence of hydrogen peroxide 1.0 g/100 ml but with the more resistant spores of 9 further strains, irradiation in the presence of hydrogen peroxide 2–5 g/100 ml followed by mild heating was required.     

The larval diet of three anisopteran (Odonata) species

SUMMARY.

• 1 Comparisons between larval diets of three anisopteran species (Anax imperator, Aeshna cyanea and Libellula depressa) showed that their food intake changed depending on: (1) predator species, (2) time of year, and (3) developmental stage.
• 2 Although this last factor is not so important, the mean size of prey items and the range of prey species eaten by Auax imperator and Aeshna cyanea larvae increased with predator size.
• 3 Comparisons between prey availability and diets indicated differential selectivity by these predators.

     

Size-dependent reproduction in Australian alpine Ranunculus

Abstract The effect of plant size on reproduction in four species of alpine Ranunculus (R. muelleri, R. dissectifolius, R. graniticola and R. niphophilus) was investigated in two sites over two seasons in the field on a total of 190 plants. The effects of plant size (number of leaves) and number of flowers on the number of anthers, ovules and seed per flower and per plant were determined. There was a positive relationship between several measures of reproduction and plant size in all four species, indicating that reproduction is size-dependent. All the results indicate that the main factor controlling the amount of seed produced by alpine Ranunculus is the size of the plant. Specifically, bigger plants produced more seed by producing more flowers, not by producing more ovules per flower, or higher seed set per flower. Correspondingly, bigger plants produced more anthers by producing more flowers, rather than by producing flowers with more anthers. The total number of seeds produced by a plant was directly proportional to plant size in the four species. Therefore, reproductive effort should not vary with plant size in the four species.     

Primary Structure and Phylogenetic Relationships of Glyceraldehyde-3-Phosphate Dehydrogenase Genes of Free-Living and Parasitic Diplomonad Flagellates

ABSTRACT. Complete nucleotide sequences have been established for two genes (gap1 and gap2) coding for glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) homologs in the diplomonad Giardia lamblia. In addition, almost complete sequences of the GAPDH open reading frames were obtained from PCR products for two free-living diplomonad species, Trepomonas agilis and Hexamita inflata, and a parasite of Atlantic salmon, an as yet unnamed species with morphological affinities to Spironucleus. Giardia lamblia gap 1 and the genes from the three other diplomonad species show high similarity to each other and to other glycolytic GAPDH genes. All amino-acyl residues known to be highly conserved in this enzyme are also conserved in these sequences. Giardia lamblia gap2 gene is more divergent and its putative translation reveals the presence of a cysteine and serine-rich insertion resembling a metal binding finger. This motif has not yet been noted in other GAPDH molecules. All sequences contain an S-loop signature with characteristics close to those of eukaryotes. In phylogenetic reconstructions based on the derived amino acid sequences with neighborjoining, parsimony and maximum-likelihood methods the four typical GAPDH sequences of diplomonads cluster into a single clade. Within this clade, G. lamblia gap1 shares a common ancestor with the rest of the genes. The latter are more closely related to each other, indicating an early separation of the lineage leading to the genus Giardia from the lineage encompassing the morphologically less differentiated genera, Trepomonas, Hexamita and that of the unnamed species. This result is discordant with the orthogonal evolution of diplomonads suggested on the basis of comparative morphology. In neighbor-joining reconstructions G. lamblia gap2 occupies a variable position, due to its great divergence. In parsimony and maximum likelihood analysis however, it shares a most recent common ancestor with the typical G. lamblia gap1 gene, suggesting that it diverged after the separation of the Giardia lineage. The position of the diplomonad clade in broader phylogenetic reconstructions is firmly within the typical cytosolic glycolytic representatives of GAPDH of eukaryotes.     

Ecdysteroids During Embryogenesis in Locusta migratoria

SYNOPSIS. Ovaries of Locusta migratoria synthesize large amountsof ecdysteroids at the end of oöcyte maturation. The predominantecdysteroids in mature ovaries are conjugated 2-deoxyecdysone(100 µM) and conjugated ecdysone (50 µM) which outnumberthe corresponding free compounds by 50–100 fold. Thesevarious ecdysteroids persist during ovulation and are recoveredfrom newly-laid eggs. The conjugated maternal ecdysteroids aregradually metabolized as embryonic development proceeds; theyhave disappeared as such on day 6 after oviposition, that isafter blastokinesis and shortly after dorsal closure. Concomitantlyto this metabolism of the maternal conjugated ecdysteroids,other ecdysteroid conjugates appear in the eggs which have differentchromatographic behaviors and some of which are conjugates ofecdysone metabolites formed by the embryo. The data availableso far are compatible with the hypothesis that the maternalconjugates are hydrolysed to free 2-deoxyecdysone and ecdysoneby the embryo during early stages of development and subsequentlyconjugated to inactivation compounds. During the later stagesof embryonic development however, a de novo synthesis of ecdysoneis probable, the maternal conjugates having been metabolizedduring the earlier stages.