Marine incursions,cryptic species and ecological diversification in Amazonia: the biogeographic history of the croaker genus Plagioscion (Sciaenidae)

Aim We propose a phylogenetic hypothesis for the marine‐derived sciaenid genus Plagioscion in the context of geomorphology and adaptation to freshwaters of South America, and assess the extent to which contemporary freshwater hydrochemical gradients influence diversification within a widely distributed Plagioscion species, Plagioscion squamosissimus. Location Amazon Basin and South America. Methods Using nuclear and mitochondrial DNA sequence data, phylogenetic analyses were conducted on the five nominal Plagioscion species, together with representatives from Pachyurus and Pachypops, using character and model‐based methods. Genealogical relationships and population genetic structure of 152 P. squamosissimus specimens sampled from the five major rivers and three hydrochemical settings/‘colours’ (i.e. white, black and clear water) of the Amazon Basin were assessed. Results Phylogenetic analyses support the monophyly of Plagioscion in South America and identify two putative cryptic species of Plagioscion. Divergence estimates suggest that the Plagioscion ancestor invaded South America via a northern route during the late Oligocene to early Miocene. Within P. squamosissimus a strong association of haplotype and water colour was observed, together with significant population structure detected between water colours. Main conclusions Our analyses of Plagioscion are consistent with a biogeographic scenario of early Miocene marine incursions into South America. Based on our phylogenetic results, the fossil record, geomorphological history and distributional data of extant Plagioscion species, we propose that marine incursions into western Venezuela between the late Oligocene and early Miocene were responsible for the adaptation to freshwaters in Plagioscion species. Following the termination of the marine incursions during the late Miocene and the establishment of the modern Amazon River, Plagioscion experienced a rapid diversification. Plagioscion squamosissimus arose during that time. The formation of the Amazon River probably facilitated population and range expansions for this species. Further, the large‐scale hydrochemical gradients within the Amazon Basin appear to be acting as ecological barriers maintaining population discontinuities in P. squamosissimus even in the face of gene flow. Our results highlight the importance of divergent natural selection through time in the generation and maintenance of sciaenid diversity in Amazonia.     

Growth Phase-Dependent Regulation of Vsr Endonuclease May Contribute to 5-Methylcytosine Mutational Hot Spots in Escherichia coli

Using rabbit polyclonal antibodies, we have shown that the Dcm cytosine methylase of Escherichia coli is maintained at a constant level during cell growth, while Vsr endonuclease levels are growth phase dependent. Decreased production of Vsr relative to Dcm during the log phase may contribute substantially to the mutability of 5-methylcytosine.     

3-Mercaptopropionic acid administration increases the affinity of [H]Quinuclidinyl benzilate binding to membranes of the striatum and cerebellum

It is known that quinuclidinyl benzilate (QNB) binds specifically and with high affinity to the cholinergic muscarinic receptor and that behaves as a potent antagonist of this receptor.

We have analysed -[³H]QNB binding to rat CNS membranes after the administration of the convulsant 3-mercaptopropionic acid (MP) (150 mg·kg⁻¹, i.p.). The studies were done in rats killed at two stages: during and after seizures. No changes in [³H]QNB binding to hippocampus and cerebral cortex membranes were found. [³H]QNB binding increased about 40 and 80% in striatum and cerebellum membranes, respectively. The changes were observed both in seizure and postseizures states. The study was extended to the assay of [³H]QNB binding kinetic constants in the anatomical areas modified by the convulsant. The analysis of the saturation curves indicated an increase in the binding affinity but no change in the number of binding sites. Hill number values were near the unit suggesting a non-cooperative interaction between the ligand and the receptor, and the labelling of a homogeneous population of receptor sites.

The results suggest the participation of some cholinergic pathways in the development and maintenance of MP-induced seizures.     

Nitrogen Source Regulates Glutamate Dehydrogenase NADP Synthesis in Neurospora crassa

Neurospora crassa glutamate dehydrogenase-NADP (EC 1.3.1.3) has a higher activity when mycelium is grown on ammonium or nitrate as nitrogen source than when grown on glutamate or glutamine. Quantitative immunoelectrophoresis established that, under all conditions, enzyme activity corresponded to enzyme concentration. Isotope incorporation studies demonstrated that the nitrogen source exerts its regulation at the level of de novo enzyme synthesis.     

Establishment of transformed root cultures of Perezia cuernavacana producing the sesquiterpene quinone perezone

Summary The sesquiterpene quinone currently known as perezone is abundantly produced by the roots of Perezia cuernavacana. This compound is of biotechnological interest since it may be used as a pigment and has several pharmacological properties. In this work we demonstrate that perezone is also produced in transformed root cultures of P. cuernavacana. Hairy roots were induced by inoculation of internodal segments of sterile plants of P. cuernavacana with Agrobacterium rhizogenes AR12 strain. The axenic liquid MS medium cultures of the hairy roots isolated from the internodes showed active growth in the absence of growth regulators. The transformed nature of the tissue was confirmed by genomic integration (PCR and slot blot hybridization) and expression (enzyme activity) of the marker gus-gene. The production of perezone by a transformed root culture was evidenced by IR spectroscopy. Our results offer an alternative for enhanced production of perezone and represent an advantage over its extraction from natural plant populations which present problems in their agronomic culture.     

Permineralized seed fern cupules from the Triassic of Antarctica: implications for cupule and carpel evolution

In this paper we describe the first anatomically preserved Mesozoic seed fern cupule–Petriellaea. The multiovulate cupules were produced singly at the end of a short dichotomizing axis. Cupules are bilateral with a dorsal groove and transverse narrow ventral opening. The vascular system of the cupule consists of a series of traces that extend up the dorsal surface of the cupule and down the ventral face. Ovules are orthotropus, sessile, and borne on the adaxial surface of the leaflike cupule either singly or in multiple rows. They are up to 1.5 mm long, triangular in transverse section, and characterized by a multilayered integument. Nucellus and integument are fused throughout their length, but no pollen chamber is present. In the chalaza is a small vascular disc of transfusion tracheids that represents the extent of the ovule vascular system. Ovules are interpreted as being fossilized at a prepollination stage, although a few possess some evidence of a cellularized megagametophyte. These permineralized cupules indicate that in at least one Mesozoic seed fern group, ovule enclosure resulted from the transverse folding (tip to petiole) of a megasporophyll bearing adaxial ovules. Cupule morphology and ovule enclosure in other Late Paleozoic and Mesozoic seed ferns is discussed.     

Diet ofColobus polykomos on Tiwai Island: Selection of food in relation to its seasonal abundance and nutritional quality

A group of Colobus polykomosat Tiwai, Sierra Leone, demonstrated seasonal flexibility in its diet, with seeds, young leaves, and mature leaves each dominating the diet at different times. Comparison of food consumption with phenological data indicates that seeds are eaten whenever available and are preferred to other foods, while young leaves are preferred to mature leaves. Colobus polykomosalso prefer liane to tree leaves, despite the relatively high quality of mature tree foliage at the Tiwai site. Analysis of protein, fiber, and energy values of foods selected and items available, but not eaten, suggests that preference is related to protein and energy maximization. Leguminous plants, especially Papilionaceae and Mimosaceae, are highlighted as important food sources for C. polykomos;seeds and leaves from these families have a high nitrogen content, and the protein content of leguminous seeds often equals or exceeds that found in leaves. It is predicted, therefore, that colobines living in habitats with a high density of legumes will feed heavily on seeds, subject to constraints such as seasonal availability. Where suitable leguminous species are less common, a mixture of fruits, seeds, and young or mature leaves or both is likely to be selected. The results of this and other recent studies of colobines do not support the notion that colobines are specialist folivores.     

Meiotic recombination in an Irish family with beta-thalassaemia

Using the technique of allele-specific priming of the polymerase chain reaction (PCR), the C-T substitution in codon 39 was identified as the cause of -thalassaemia in an Irish family. Analysis of the restriction fragment length polymorphisms (RFLPs) in the -globin gene cluster established linkage of the -thalassaemia mutation to a particular -haplotype but indicated that a recombinational event had occurred in the paternal chromosome in the younger of two affected children. Non-paternity was excluded by DNA fingerprinting analysis with hypervariable minisatellite probes. This is the fourth case of recombination in the -globin gene cluster to be reported. The event has occurred 5 of the polymorphic RsaI site at position-550 bp upstream of the -globin gene mRNA Cap site, within the 9.1-kb region that has been shown to be a hot spot for recombination in the -globin gene cluster.     

An endogenous factor which interacts with synaptosomal membrane Na+, K+-ATPase activation by K+

In previous papers, the isolation of brain soluble fractions able to modify neuronal Na⁺, K⁺-ATPase activity has been described. One of those fractions-peak I-stimulates membrane Na⁺, K⁺-ATPase while another-peak II-inhibits this enzyme activity, and has other ouabain-like properties. In the present study, synaptosomal membrane Na⁺, K⁺-ATPase was analyzed under several experimental conditions, using ATP orp-nitrophenylphosphate (p-NPP) as substrate, in the absence and presence of cerebral cortex peak II. Peak II inhibited K⁺-p-NPPase activity in a concentration dependent manner. Double reciprocal plots indicated that peak II uncompetitively inhibits K⁺-p-NPPase activity regarding substrate, Mg²⁺ and K⁺ concentration. Peak II failed to block the known K⁺-p-NPPase stimulation caused by ATP plus Na⁺. At various K⁺ concentrations, percentage K⁺-p-NPPase inhibition by peak II was similar regardless of the ATP plus Na⁺ presence, indicating lack of correlation with enzyme phosphorylation. Na⁺, K⁺-ATPase activity was decreased by peak II depending on K⁺ concentration. It is postulated that the inhibitory factor(s) present in peak II interfere(s) with enzyme activation by K⁺.