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.     

Use-dependent block of the voltage-gated Na+ channel by tetrodotoxin and saxitoxin: Effect of pore mutations that change ionic selectivity

Voltage-gated Na⁺ channels (NaV channels) are specifically blocked by guanidinium toxins such as tetrodotoxin (TTX) and saxitoxin (STX) with nanomolar to micromolar affinity depending on key amino acid substitutions in the outer vestibule of the channel that vary with NaV gene isoforms. All NaV channels that have been studied exhibit a use-dependent enhancement of TTX/STX affinity when the channel is stimulated with brief repetitive voltage depolarizations from a hyperpolarized starting voltage. Two models have been proposed to explain the mechanism of TTX/STX use dependence: a conformational mechanism and a trapped ion mechanism. In this study, we used selectivity filter mutations (K1237R, K1237A, and K1237H) of the rat muscle NaV1.4 channel that are known to alter ionic selectivity and Ca²⁺ permeability to test the trapped ion mechanism, which attributes use-dependent enhancement of toxin affinity to electrostatic repulsion between the bound toxin and Ca²⁺ or Na⁺ ions trapped inside the channel vestibule in the closed state. Our results indicate that TTX/STX use dependence is not relieved by mutations that enhance Ca²⁺ permeability, suggesting that ion–toxin repulsion is not the primary factor that determines use dependence. Evidence now favors the idea that TTX/STX use dependence arises from conformational coupling of the voltage sensor domain or domains with residues in the toxin-binding site that are also involved in slow inactivation.     

Predictive Dynamics of Human Pain Perception

While the static magnitude of thermal pain perception has been shown to follow a power-law function of the temperature, its dynamical features have been largely overlooked. Due to the slow temporal experience of pain, multiple studies now show that the time evolution of its magnitude can be captured with continuous online ratings. Here we use such ratings to model quantitatively the temporal dynamics of thermal pain perception. We show that a differential equation captures the details of the temporal evolution in pain ratings in individual subjects for different stimulus pattern complexities, and also demonstrates strong predictive power to infer pain ratings, including readouts based only on brain functional images.     

THE TIME AND SITE OF THE SEMIDOMINANT LETHAL ACTION OF “Wo” IN LYCOPERSICON ESCULENTUM

Huang , P. C. (California Inst. Technol., Pasadena), and E. F. Paddock . The time and site of the semidominant lethal action of “Wo” in Lycopersicon esculentum. Amer. Jour. Bot. 49(4): 388–393. Illus. 1962.—The semidominant lethal gene, Wo (Woolly), in Lycopersicon esculentum has been investigated with specific attention to its lethal action. The primary lethal action is believed to occur prior to the torpedo stage of embryonic development (approximately 22 days after anthesis). The presumed WoWo embryos cease to grow before any cambial differentiation or organogenesis can be recognized. Their accompanying endospermous cells, however, continue to divide, this resulting in full-sized seeds. The death of these embryos probably occurs near the time of maturation of the seeds (approximately 52 days after anthesis or when the ovulary turns orange-red). The mechanism of death of the embryo apparently lies in and is specific to the embryo; hence, this is a case of autogenously determined embryonic lethality.     

Cloning and characterization of a 9-lipoxygenase gene induced by pathogen attack from <Emphasis Type="Italic">Nicotiana benthamiana</Emphasis>for biotechnological application

Background  

Plant lipoxygenases (LOXs) have been proposed to form biologically active compounds both during normal developmental stages such as germination or growth as well as during responses to environmental stress such as wounding or pathogen attack. In our previous study, we found that enzyme activity of endogenous 9-LOX in Nicotiana benthamiana was highly induced by agroinfiltration using a tobacco mosaic virus (TMV) based vector system.     

Toxicity of Blastomyces dermatitidis

Following injections of the insoluble portion of disrupted yeast cells ofBlastomyces dermatitidis animals exhibited a biphasic pyrogenic response, a decrease in total serum proteins, and there was no release of interferon.     

Nucleotide sequence and properties of the cohesive DNA termini from bacteriophage HP1c1 of Haemophilus influenzae Rd

The termini of the mature DNA of phage HP1c1 of Haemophilus influenzae Rd have been characterized by DNA ligation, nucleotide sequencing, and deoxynucleotide incorporation experiments. A hybrid plasmid containing the joined phage termini (the cos site) inserted into pBR322 has been constructed. The phage DNA has cohesive termini composed of complementary 5' single-stranded extensions which are seven residues long. The left cohesive terminal extension consists only of pyrimidines and the right only of purines. When the ends of the phage are joined, the terminal sequences constitute the central 7 bp of an 11 bp sequence containing only purines on one strand and pyrimidines on the other strand. This oligopyrimidine/oligopurine sequence does not possess rotational symmetry. A 10-bp sequence and its inverted repeat are located approx. 20 bp to the left and right of the fused ends.     

Nucleotide sequence and topography of chicken c-fps. Genesis of a retroviral oncogene encoding a tyrosine-specific protein kinase

We isolated molecular clones of chicken DNA that carry portions of the cellular proto-oncogene c-fps and then determined the nucleotide sequence of all regions of the gene that are related to the retroviral oncogene v-fps. The homology of v-fps within c-fps resides on at least 19 interspersed segments, 17 of which represent complete exons and two of which may represent only portions of exons. Fusion of these segments reconstructs a facsimile of v-fps. The arrangement of introns and exons within c-fps differs from that of the related proto-oncogene c-src in the domains of the two genes that encode tyrosine-specific protein kinase activity. It therefore appears likely that the introns arose subsequent to the gene duplication that engendered c-src and c-fps. The data also reveal potential junctions between viral and cellular domains in the genomes of two independently isolated avian sarcoma viruses (the PRCII and Fujinami strains). The lefthand junctions can be well defined: they occur at the same position in c-fps but at different positions in the viral gene gag. The righthand junctions cannot be defined as precisely because they include a sequence of 10 to 15 nucleotides whose origin is not known. In the genome of PRCII virus, the composition of this sequence suggests that it arose from the polyadenylated 3' terminus of the c-fps messenger RNA. If this deduction proves to be correct, the data will provide direct evidence that the righthand recombination during transduction by retroviruses occurs between RNA intermediates. Irrespective of these ambiguities, both junctions are located within exons of c-fps, and both may have been formed by non-homologous recombination (although the evidence for the latter statement is not decisive). A sequence of 1020 nucleotides has been deleted from the transduced version of c-fps in the genome of PRCII virus, apparently by homologous recombination between sequences repeated within c-fps. Fujinami virus may contain the entire coding domain of c-fps, but mutations have created 26 amino acid substitutions in the viral version of the gene. By contrast, the partially deleted version of c-fps in PRCII virus contains no mutations that would alter the amino acid sequence.