Tremorgenic mycotoxins produced by strains of Penicillium spp. isolated from toxic Poa huecu parodi

Seventeen strains of Penicillium spp. have been isolated from Poa huecu Parodi from the Zapala zone, exhibiting toxicity to sheet. The following strains have been identified: P. crustosum, cyclopium, notatum, palitans, puberulum, verrucosum, viridicatum and Penicillium spp. The toxigenic capacity of the strains was studied after growing them under suitable conditions. Toxins produced were analysed by thin layer chromatography (TLC). Penitrem A (PA) and Penitrem B (PB) neurotoxins were identified and quantitated in twelve strains; verruculogen (VERR) and fumitremorgen B (FTB) being present in one of them. The effect of these mycotoxins was studied in mice. Neurological symptoms characteristic of the intoxication by tremorgenic toxins and similar to those observed in sheep suffering from huecu's disease were observed. The possible role of these toxins as causative agents of huecu's disease is discussed.     

Home range of newborn blacktip reef sharks (Carcharhinus melanopterus), as estimated using mark-recapture and acoustic telemetry

Coral Reefs - Sharks play important functional roles in coral reef ecosystems. Studying reef shark populations’ spatial ecology also contributes important data for effective conservation...     

A Surface-Induced Asymmetric Program Promotes Tissue Colonization by Pseudomonas aeruginosa

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Extended phenotypes and foraging restrictions: ant nest entrances and resource ingress in leaf‐cutting ants

Several factors may restrict the acquisition of food to below the levels predicted by the optimization theory. However, how the design of structures that animals build for foraging restricts the entry of food is less known. Using scaling relationships, we determined whether the design of the entrances of leaf‐cutting ant nests restricts resource input into the colony. We measured nests and foraging parameters in 25 nests of Atta cephalotes in a tropical rain forest. Ant flux was reduced to up to 60% at nest entrances. The width of all entrances per nest increased at similar rates as nest size, but the width of nest entrances increased with the width of its associated trail at rates below those expected by isometry. The fact that entrance widths grow slower than trail widths suggests that the enlargement of entrance holes does not reach the dimensions needed to avoid delays when foraging rates are high and loads are big. The enlargement of nest entrances appears to be restricted by the digging effort required to enlarge nest tunnels and by increments in the risk of inundation, predator/parasitoid attacks and microclimate imbalances inside the nest. The design of the extended phenotypes can also restrict the ingress of food into the organisms, offering additional evidence to better understand eventual controversies between empirical data and the foraging theory. Abstract in Spanish is available with online material.     

A network-based approach to integrate nutrient microenvironment in the prediction of synthetic lethality in cancer metabolism

Synthetic Lethality (SL) is currently defined as a type of genetic interaction in which the loss of function of either of two genes individually has limited effect in cell viability but inactivation of both genes simultaneously leads to cell death. Given the profound genomic aberrations acquired by tumor cells, which can be systematically identified with -omics data, SL is a promising concept in cancer research. In particular, SL has received much attention in the area of cancer metabolism, due to the fact that relevant functional alterations concentrate on key metabolic pathways that promote cellular proliferation. With the extensive prior knowledge about human metabolic networks, a number of computational methods have been developed to predict SL in cancer metabolism, including the genetic Minimal Cut Sets (gMCSs) approach. A major challenge in the application of SL approaches to cancer metabolism is to systematically integrate tumor microenvironment, given that genetic interactions and nutritional availability are interconnected to support proliferation. Here, we propose a more general definition of SL for cancer metabolism that combines genetic and environmental interactions, namely loss of gene functions and absence of nutrients in the environment. We extend our gMCSs approach to determine this new family of metabolic synthetic lethal interactions. A computational and experimental proof-of-concept is presented for predicting the lethality of dihydrofolate reductase (DHFR) inhibition in different environments. Finally, our approach is applied to identify extracellular nutrient dependences of tumor cells, elucidating cholesterol and myo-inositol depletion as potential vulnerabilities in different malignancies.     

Temporal change in the genetic structure between and within cohorts of a marine fish,Diplodus sargus,induced by a large variance in individual reproductive success

Temporal changes at 16 allozyme loci in the Diplodus sargus population of Banyuls-sur-Mer (Mediterranean Sea, France) were monitored. Temporal genetic variation within a single population was examined over two temporal scales: (i) among three year-classes sampled at the same age, and (ii) within a single year-class sampled three times over a two-year period. We observed a significant change in the genotypic structure within the same cohort during the first two years following settlement and before recruitment into the adult population. In addition, comparison of year-classes showed that cohorts differed significantly one year after settlement, whereas they became similar later on before recruitment into the adult population. The observed changes in the genetic structure within and between year-classes may be the result of complex selective processes or genetic drift. Linkage disequilibrium and genetic relatedness data suggest that these changes are due to large variation in reproductive success, followed by homogenization through adult movement. Overall, these results demonstrated a rapid genetic change within a population.     

Genetic evidence of closed life-cycles for some coral reef fishes within Taiaro Lagoon (Tuamotu Archipelago, French Polynesia)

 Taiaro Lagoon has no permanent or regular connection with the ocean (ingress is restricted to episodes of high sea-level and/or strong wave action) raising the question of how fish populations with normally dispersive larvae are maintained inside this lagoon. We compared the genetic population structures of two coral reef fishes, Acanthurus triostegus and Chaetodon ulietensis, present on both sides of the atoll rim to determine whether there is evidence of reproductive isolation. Genetic surveys showed that the lagoonal and oceanic populations were statistically different at five loci (AAT ^* -3, GDA ^*, HPD ^*, MDH ^* and SDH ^*) in A. triostegus and three loci (PGI-2^*, IDH ^* and PGD ^*) in C. ulietensis, producing high F _st values of 0.055 and 0.021, respectively. Our genetic and demographic data on these species suggest that both may be completing their life-cycles inside the lagoon, which leads us to question the common assumption that coral reef fishes require oceanic conditions for larval development. Accepted: 28 August 1997     

Inferring gene flow in coral reef fishes from different molecular markers: which loci to trust?

Contrasting results are usually reported in the literature regarding the factors influencing observed structuring of genetic variability. The goals of this study were, for five coral reef fishes in French Polynesia, (1) to infer the theoretical variance of single locus F(ST) estimates expected under neutrality in order to exclude outlier loci before inferring gene flow and (2) to test thereafter whether species laying pelagic eggs effectively disperse more than species laying benthic eggs in this system. For this purpose, a total of 952 individuals from five species belonging to two families (Chaetodontidae and Pomacentridae) were screened among populations sampled within a 60-600 km spatial range for intron length polymorphism at 11 loci in order to illuminate contrasting results previously published on allozymes and mitochondrial DNA (mtDNA) control region polymorphisms. Statistically speaking, among the five species, four loci (three allozymes and one intron) were identified as outliers and discarded before interpretation of genetic differentiation in terms of effective dispersal. Biologically speaking, our results suggest that the observed genetic structure is not significantly related to the reproductive strategy of coral reef fish in the island system we analysed and that observed random genetic differentiation accommodates Wright's island model in all five species surveyed. Overall, our study emphasizes how cautious one has to be when trying to interpret present-day genetic structure in terms of gene flow while using a limited number of loci and/or different sets of loci.     

Recovering metabolic pathways via optimization

A metabolic pathway is a coherent set of enzyme catalysed biochemical reactions by which a living organism transforms an initial (source) compound into a final (target) compound. Some of the different metabolic pathways adopted within organisms have been experimentally determined. In this paper, we show that a number of experimentally determined metabolic pathways can be recovered by a mathematical optimization model.     

Individual-based analysis opens new insights into understanding population structure and animal behaviour

Studying the movement of individuals in the wild has always been a challenge in ecology. However, estimating such movement is essential in life sciences as it is the base-line for evaluating connectivity, a major component in developing management and conservation plans. Furthermore, movement, or migration, is an essential parameter in population genetics, as it directly affects genetic differentiation. The development of highly variable markers has allowed genetic discrimination between individuals within populations and at larger scales, and the availability of high-throughput technologies means that many samples and hence many individuals can be screened. These advances mean that we can now use genetic identification for tracking individuals, and hence follow both survival and reproductive output through the life cycle. The paper by Morrissey & Ferguson (2011, this issue) is a demonstration of this new capability, as authors were able to infer the movement of salmonid fish initially captured as juveniles, and later as reproductively mature adults.