Direct and indirect effects of exotic annual grasses on species composition of a South Australian grassland

Abstract Invasion by Mediterranean annual grasses, such as Avena L. spp. and Bronms L. spp, is one of the major threats to temperate perennial grassland. This study investigated the effects of annual grasses and their litter on the species composition of a grassland near Burra, South Australia. The placement of annual grass litter on soil samples in the glasshouse decreased the establishment or growth of several exotic annual dicots. In the field the addition of annual grass litter slightly decreased the frequency of Danthonia Lam. & DC. tussocks. Furthermore, litter strongly reduced the species richness from 13 species in plots with no litter to nine species in plots with the highest litter level, mainly by decreasing the frequency of common exotic dicots. Native dicot frequency similarly appeared to be decreased by litter addition. In addition to the negative effects of their litter, annual grasses also directly competed with perennial grasses. The magnitude of the competitive effect varied systematically along a slope, suggesting that other factors such as soil properties may control competitive inter actions. The biomass of annual grasses also tended to increase with the addition of their own litter. This combination of positive and negative feedback mechanisms suggests that brief periods favourable for annual grasses, either through management changes or environmental conditions, can lead to persistent changes in the species composition of the system.     

Blood Biochemistry of Sea Turtles Captured in Gillnets in the Lower Cape Fear River,North Carolina,USA

ABSTRACT Mortality due to fisheries interactions has been implicated as a contributor to population decline for several species of sea turtle. The incidental capture of sea turtles in the coastal gillnet fisheries of North Carolina, USA, has received much attention in recent years, and mitigation measures to reduce sea turtle mortality due to gillnet entanglement are a high priority for managers and conservationists. Efforts to evaluate effects of gillnet entanglement on sea turtle populations are complicated by the lack of information on health status of turtles released alive from nets and postrelease mortality. We obtained blood samples from green (Chelonia mydas) and Kemp's ridley (Lepidochelys kempii) sea turtles captured in gillnets for 20–240 minutes to assess the impacts of gillnet entanglement on blood biochemistry and physiological status. We measured concentrations of lactate, corticosterone, ions (Na⁺, K⁺, Cl^-, P, Ca²⁺), enzymes (lactate dehydrogenase [LDH], creatine phosphokinase [CPK], aspartate aminotransferase [AST]), protein, and glucose in the blood and also performed physical examinations of turtles to document external indicators of health status (injuries, lethargy, muted reflexes). We evaluated the effects of entanglement time on blood biochemistry and to look for correlations between blood biochemistry and results of the physical examinations. We observed a significant increase in blood lactate, LDH, CPK, phosphorus, and glucose with increased entanglement time. Alterations in blood biochemistry were generally associated with a decline in health status as indicated by results of the physical examination. Although entanglement time plays an important role in determining the health status of sea turtles upon release from a gillnet, our results suggest that factors such as the depth and severity of entanglement may also have an effect on health status of turtles and the probability of postrelease survival. We were unable to set a maximum unattended gillnet soak time to minimize impacts on captured sea turtles, and therefore recommend that fisheries managers continue to enforce the net attendance regulations currently in place in the lower Cape Fear River, North Carolina, during the summer months.     

Origin and maintenance of sex: the evolutionary joys of self sex

Sex is generally thought of as meiosis, conjugation, and syngamy, with the primary function of sex believed to be genetic mixing. However, conjugation does not occur with complete automixis, whereas syngamy does not occur with restitutional automixis. Self sex in the forms of automixis and autogamy does not include genetic mixing. Yet sex, including self sex, is necessary for most eukaryotic lineages. What is the purpose of sex without genetic mixing? Obligate self sex is not an evolutionary dead end, but holds the key to understanding the evolutionary origin, function, maintenance, and ubiquity of sex. We extend the rejuvenescence hypothesis that sex provides a necessary developmental reset for multicellular eukaryotes and even many unicellular eukaryotes. Sex reduces additive genetic variance of epigenetic signals, especially cytosine methylation, and of ploidy levels. Furthermore, we argue that syngamy is a modified form of meiosis that maintains ploidy and resets epigenetic signals. Epigenetic resetting is consistent with sex being induced by starvation or desiccation. Diminution of additive genetic variance is consistent with the origin and maintenance of an adaptive trait, sex, that has been present for approximately two billion years. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 707–728.     

Male-limited evolution suggests no extant intralocus sexual conflict over the sexually dimorphic cuticular hydrocarbons of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Sexually dimorphic traits are likely to have evolved through sexually antagonistic selection. However, recent empirical data suggest that intralocus sexual conflict often persists, even when traits have diverged between males and females. This implies that evolved dimorphism is often incomplete in resolving intralocus conflict, providing a mechanism for the maintenance of genetic variance in fitness-related traits. We used experimental evolution in Drosophila melanogaster to directly test for ongoing conflict over a suite of sexually dimorphic cuticular hydrocarbons (CHCs) that are likely targets of sex-specific selection. Using a set of experimental populations in which the transmission of genetic material had been restricted to males for 82 generations, we show that CHCs did not evolve, providing experimental evidence for the absence of current intralocus sexual conflict over these traits. The absence of ongoing conflict could indicate that CHCs have never been the target of sexually antagonistic selection, although this would require the existing dimorphism to have evolved via completely sexlinked mutations or as a result of former, but now absent, pleiotropic effects of the underlying loci on another trait under sexually antagonistic selection. An alternative interpretation, and which we believe to be more likely, is that the extensive CHC sexual dimorphism is the result of past intralocus sexual conflict that has been fully resolved, implying that these traits have evolved genetic independence between the sexes and that genetic variation in them is therefore maintained by alternative mechanisms. This latter interpretation is consistent with the known roles of CHCs in sexual communication in this species and with previous studies suggesting the genetic independence of CHCs between males and females. Nevertheless, direct estimates of sexually antagonistic selection will be important to fully resolve these alternatives.     

Activity of the Pentose Phosphate and Glycolytic Pathways During Anaerobic Germination of Echinochloa crus-galli (barnyard grass) Seeds

Changes in the activity of key enzymes in glycolysis and theoxidative pentose phosphate pathway were studied in Echinochloacrus-galli (L.) Beauv. var. oryzicola seeds during germinationin air or nitrogen. In addition, the metabolism of specificallylabelled [^I4C]glucose was followed to evaluate the activityof both pathways during anaerobic germination. During the 7 d time period studied there was no difference betweenair and nitrogen in phosphofructokinase activity. Under anaerobicconditions, fructose-1, 6-bisphosphate aldolase increased morethan two-fold in 7 d; whereas in air, it decreased. The activityof the pentose phosphate pathway enzyme, glucose-6-phosphatedehydrogenase, increased under N₂ until day three, when it levelledoff, whilst it continued to increase up to day seven in air. Incubation of Echinochloa seedlings with specifically labelledglucose also resulted in differences between anaerobic- andair-grown seedlings. Labelling of phosphorylated sugars andlipids predominated under N₂; whereas in air, malate and fumaratewere the most heavily labelled compounds. In both air and N₂,there was a greater percentage of label in CO2 from [l-¹⁴C]glucose,while [6-14C] resulted in a greater percentage label in ethanol.These differences were more pronounced under N2, especiallyduring the first 24 h of imbibition, suggesting increased activityof the pentose phosphate pathway. Key words: Echinochloa, Anaerobic metabolism, Oxidative pentose phosphate pathway     

Encystment of Pythium aphanidermatum Zoospores is Induced by Root Mucilage Polysaccharides, Pectin and a Monoclonal Antibody to a Surface Antigen

The infection of roots by the pathogenic Oomycete Pythium aphanidermatuminvolves interactions between the fungal zoospores and rootsurface mucilage polysaccharides. After initial recognitionat the root surface the zoospores are triggered to encyst duringwhich adhesive glycoproteins are secreted followed by a fibrillarcyst wall. In this paper a simple in vitro assay has been usedto assess the ability of a variety of macromolecules to inducezoospore encystment. Mucilage polysaccharides of the cress rootsurface trigger encystment. Whole mucilage was fractionatedby gel filtration and a fraction low in uronic acid, containing5% fucose, was shown to be more effective in triggering encystmentthan a uronic acid-rich fraction. Encystment can also be inducedby commercial pectin. The lectin Con A, and PA1, one of a rangeof monoclonal antibodies specific for zoospore surface antigens,also triggered encystment. In Western blotting experiments PA1recognizes protein epitopes of a 75 kDa surface antigen. Theresults suggest that at least one mechanism of zoospore triggeringmay involve a specific zoospore surface receptor. Key words: Pythium aphanidermatum, recognition, encystment, zoospore, mucilage, root, monoclonal antibodies, polysaccharides     

The visual system of the alligator

The eye tissues and liver of the alligator contain vitamin A₁ alone. The retina contains rhodopsin, typical in absorption spectrum (λ_max 500 mµ); but synthesized in solution from neo-b retinene and opsin much more rapidly than are the frog, mammalian, or chicken rhodopsins previously examined. In this regard alligator rhodopsin resembles the rhodopsins and porphyropsins of fishes, all of which so far investigated are synthesized rapidly in solution. The rates of synthesis in vitro of frog and alligator rhodopsins are matched closely by the rates of rod dark adaptation in living frogs and alligators, measured electrophysiologically at the same temperature. Alligator rods dark-adapt, and alligator rhodopsin is synthesized in solution, at rates characteristically associated with cones and cone pigments in frogs, mammals, and birds.