In vitro Inhibition of Oocyte and Follicular Maturation and Spawning in Starfish (Asterias forbesi) by 2-4-Dinitrophenol

The in vitro effects of 2-4-dinitrophenol (DNP) on spawning and follicular and oocyte maturation in starfish ovaries and its various cellular components were investigated. Spawning and oocyte and follicular maturation induced by starfish gonadotropin radial nerve factor (RNF) in isolated ovarian fragments were all inhibited by appropriate doses of DNP. DNP inhibits processes which occur shortly after addition of the gonadotropin; in ovarian fragments insensitivity to DNP inhibition occurred shortly after addition of RNF but prior to initiation of spawning. Spontaneous follicular and oocyte maturation which occurred following release of ovarian follicles into sea water was prevented by DNP. In non-spontaneously maturing follicles released from the ovary, DNP inhibited both follicle and oocyte maturation induced by the secondary stimulator of spawning and maturation, 1-methyladenine (1-MA). DNP also inhibited 1-MA induced meiotic maturation in isolated immature oocytes incubated in the absence of follicle cells. Inhibition of oocyte maturation was not associated with inhibition of ³H-1-MA incorporation by isolated oocytes. Immature oocytes incubated in the presence of DNP underwent maturation following washing and subsequent exposure to 1-MA. Immature oocytes initially exposed to both 1-MA and DNP, however, showed decreased maturation responsiveness following washing and re-exposure to 1-MA. The results suggest that the inhibitory effects of DNP on spawning and oocyte maturation are the result of direct effects on the oocytes and possibly other cells and tissues within the ovary.     

Century‐scale records of coral growth rates indicate that local stressors reduce coral thermal tolerance threshold

Coral bleaching, during which corals lose their symbiotic dinoflagellates, appears to be increasing in frequency and geographic extent, and is typically associated with abnormally high water temperatures and solar irradiance. A key question in coral reef ecology is whether local stressors reduce the coral thermal tolerance threshold, leading to increased bleaching incidence. Using tree‐ring techniques, we produced master chronologies of growth rates in the dominant reef builder, massive Montastraea faveolata corals, over the past 75–150 years from the Mesoamerican Reef. Our records indicate that the 1998 mass bleaching event was unprecedented in the past century, despite evidence that water temperatures and solar irradiance in the region were as high or higher mid‐century than in more recent decades. We tested the influence on coral extension rate from the interactive effects of human populations and thermal stress, calculated here with degree‐heating‐months (DHM). We find that when the effects of chronic local stressors, represented by human population, are taken into account, recent reductions in extension rate are better explained than when DHM is used as the sole predictor. Therefore, the occurrence of mass bleaching on the Mesoamerican reef in 1998 appears to stem from reduced thermal tolerance due to the synergistic impacts of chronic local stressors.     

Biofuels agriculture: landscape‐scale trade‐offs between fuel,economics, carbon,energy, food,and fiber

First‐generation biofuels are an existing, scalable form of renewable energy of the type urgently required to mitigate climate change. In this study, we assessed the potential benefits, costs, and trade‐offs associated with biofuels agriculture to inform bioenergy policy. We assessed different climate change and carbon subsidy scenarios in an 11.9 million ha (5.48 million ha arable) region in southern Australia. We modeled the spatial distribution of agricultural production, full life‐cycle net greenhouse gas (GHG) emissions and net energy, and economic profitability for both food agriculture (wheat, legumes, sheep rotation) and biofuels agriculture (wheat, canola rotation for ethanol/biodiesel production). The costs, benefits, and trade‐offs associated with biofuels agriculture varied geographically, with climate change, and with the level of carbon subsidy. Below we describe the results in general and provide (in parentheses) illustrative results under historical mean climate and a carbon subsidy of A$20 t^?1 CO₂^?e. Biofuels agriculture was more profitable over an extensive area (2.85 million ha) of the most productive arable land and produced large quantities of biofuels (1.7 GL yr^?1). Biofuels agriculture substantially increased economic profit (145.8 million $A yr^?1 or 30%), but had only a modest net GHG abatement (?2.57 million t CO₂^?e yr^?1), and a negligible effect on net energy production (?0.11 PJ yr^?1). However, food production was considerably reduced in terms of grain (?3.04 million t yr^?1) and sheep meat (?1.89 million head yr^?1). Wool fiber production was also substantially reduced (?23.19 kt yr^?1). While biofuels agriculture can produce short‐term benefits, it also has costs, and the vulnerability of biofuels to climatic warming and drying renders it a myopic strategy. Nonetheless, in some areas the profitability of biofuels agriculture is robust to variation in climate and level of carbon subsidy and these areas may form part of a long‐term diversified mix of land‐use solutions to climate change if trade‐offs can be managed.     

Species-richness of the Anopheles annulipes complex (Diptera: Culicidae) revealed by tree and model-based allozyme clustering analyses

The Australasian Anopheles annulipes complex contains at least ten sibling species, some of which are important vectors of myxomatosis in rabbits. We aimed to establish how many species occurred among specimens from 61 sites throughout Australia, scored for 32 putative allozyme loci. We compared the number of species predicted from tree-based clustering of operational taxonomic units (OTUs) with that from a novel model-based Bayesian clustering approach for individual genotypes. We rejected the hypothesis of conspecificity of OTUs if they differed by at least 20% fixed differences and 0.300 Nei's standard genetic distance D . According to these criteria, 18–25 species occur, making this the most species-rich anopheline complex known to date. A conservative estimate from the Bayesian analysis was 15–20 species. There was large overlap in the assignment of individuals to clusters inferred from the Bayesian and tree-based analyses. The genetic clustering of northern and southern distributed species and an apparent cline in alleles of the enzyme glucose phosphate isomerase suggest that a latitude-dependent factor, such as temperature, may have played a role in speciation and the subsequent distribution of species. Ecological niche modelling of clusters predicted that none occur in New Guinea, emphasizing that additional, as yet unsampled, species may occur.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 523–539.     

Temperature and the effects of elemental food quality on Daphnia

1. We examined the responses of two species of Daphnia to changes in food phosphorus (P) content, with animals reared at three different water temperatures. Specifically, we measured mass‐specific growth rate (MSGR), body P content and respiration rate of Daphnia magna and Daphnia pulex acclimatised to 10, 17.5 and 25 °C and fed food carbon : phosphorus (C : P) ratios of either 150 or 500. 2. The responses of these three physiological variables to temperature–food quality interactions were species‐specific. There was a significant interactive effect of temperature and food quality on D. magna, as the greatest proportional effect of food quality on growth was observed at 10 °C and reductions in body P because of low food P content were relatively greater at 25 °C. These effects may reflect the temperature dependence of mechanisms that reduce elemental constraints associated with food quality in D. magna. By contrast, there were no interactive effects between food quality and temperature on MSGR, body P or mass‐specific respiration of D. pulex. 3. It thus appears that temperature can alter food quality effects on Daphnia but the nature of these alterations depends upon the daphniid species and its thermal adaptability. Significant temperature–food quality interactions will complicate efforts to understand zooplankton nutrition in nature and warrant future consideration.     

Another quarter century of great progress in understanding the biological properties of plant viruses

The last quarter century saw a massive application of new molecular and cell biological, and molecular genetical, techniques in research on plant viruses. Hundreds of complete virus genomic nucleotide sequences were analysed, their constituent genes and control elements identified, and similarities and differences revealed in genome organisation, so justifying the modern taxonomic classification of the viruses. Numerous virus replication systems were described and some viral replicases isolated. Especially good progress was made in understanding cell‐to‐cell and long‐distance virus transport within plants; in cloning dominant and recessive plant genes controlling virus resistances, and identifying the cognate viral avirulence factors; in unraveling mechanisms of virus transmission by invertebrate and plasmodiophorid vectors; and in showing through these advances how viruses utilise and subvert endogenous eukaryotic processes. The discovery of gene silencing, and of viral silencing‐suppressor proteins, transformed ideas on how virus replication is controlled, and explained the phenomena of recovery from disease, cross‐protection between virus strains and synergy between unrelated viruses. Transgenic, virus‐resistant plants were created, tested successfully in field conditions and a few commercialised. Factors underlying the appearance of new disease epidemics were identified. Genetic recombination was reported and found to make an important contribution to generating virus variation, and some major virus evolutionary pathways were recognised by comparative genome analysis. The scene is set for further major advances in the coming decades.     

Two's company,three's a crowd: new insights on spruce budworm species boundaries using genotyping‐by‐sequencing in an integrative species assessment (Lepidoptera: Tortricidae)

Species delimitation requires an assessment of varied traits that can contribute to reproductive isolation, as well as of the permanence of evolutionary differentiation among closely related lineages. Integrative taxonomy, including the combination of genome‐wide molecular data with ecological data, offers an effective approach to this issue. We use genotyping‐by‐sequencing together with a review of ecological divergence to assess the traditionally recognized species status of three closely related members of the spruce budworm species complex, Choristoneura fumiferana (Clemens), C. occidentalis Freeman (=C. freemani Razowski) and C. biennis Freeman, each of which is a major defoliator of conifer forests. We sampled a broad region of overlap between these three taxa in Alberta and British Columbia (Canada) where potential for gene flow provides a strong test of the durability of divergence among lineages. A total of 2218 single nucleotide polymorphisms (SNPs) were assayed, and patterns of differentiation were evaluated under the biological, ecological, genotypic cluster and phylogenetic species concepts. Choristoneura fumiferana was genetically distinct with substantial barriers to genetic exchange with C. occidentalis and C. biennis. Conversely, divergence between C. occidentalis and C. biennis was limited to a small subset of outlier loci and was within the range observed within any one of the taxa. Considering both population genetic and ecological patterns of divergence, C. fumiferana should continue to be recognized as a distinct species, and C. biennis ( syn.n. ) should be treated as a subspecies (C. occidentalis biennis Freeman, 1967) of C. occidentalis, thereby automatically establishing the nominate name C. occidentalis occidentalis Freeman, 1967 for univoltine populations of this species.     

Management and Conservation Article

Abstract Despite increased knowledge about environmental toxins and changes in lead use (i.e., the mandated use of nonlead paint, gasoline, and shotgun pellets used for hunting waterfowl on federal lands), lead poisoning continues to occur in terrestrial birds. The degree of exposure and its demographic effect, however, continue to be described, emphasizing the growing concern over lead exposure. We examined 302 blood samples from common ravens (Corvus corax) scavenging on hunter-killed large ungulates and their offal piles to determine if lead rifle-bullet residuum was a point source for lead ingestion in ravens. We took blood samples during a 15-month period spanning 2 hunting seasons. Of the ravens tested during the hunting season, 47% exhibited elevated blood lead levels (≥ 10 μg/dL) whereas 2% tested during the nonhunting season exhibited elevated levels. Females had significantly higher blood lead levels than did males. Our results confirm that ravens are ingesting lead during the hunting season and are likely exposed to lead from rifle-shot big-game offal piles.