Fly pollination of Linum lewish (Linaceae)

This study examines the reproductive biology of Linum lewisii Pursh. (Linaceae), a polyphilic species visited by small bees and generalist flies in montane Colorado. L. lewisii plants growing at different sites experience large temporal and spatial variations in pollinator visits. Their ability to attract both dipteran and hymenopteran pollinators allows pollination under varying conditions as pollinator pool composition changes. Although L. lewisii is self-compatible, hand-pollination studies indicate that insects are required for seed production. The relative effectiveness of fly and bee pollinators is assessed in terms of per-visit pollen deposition. Insect visitation patterns are combined with per-visit effectiveness data to evaluate the relative importance of different pollinator groups. Overall, bees tend to be more effective than flies in depositing pollen. However, in many instances flies appear to be responsible for more pollen deposition due to their higher visitation rates.     

The benefit to some minnows of spawning in the nests of other species

Synopsis Fishes that act as nest associates spawn simultaneously with nest-building hosts and then abandon their eggs. The proposed benefit for this behavior is increased brood survivorship, arising from the physical environment provided by the nest or the parental care provided by the host. Field and enclosure experiments indicated that associates benefit from the parental care provided by the host, and not from the physical environment provided by the nests of hosts. This information, along with the effect of nest association on host reproductive success, is necessary before the nature of this nesting symbiosis can be characterized.     

How does the G protein,Gi2, transduce mitogenic signals?

Serpentine receptors coupled to the heterotrimeric G protein, G_i2, are capable of stimulating DNA synthesis in a variety of cell types. A common feature of the G_i2-coupled stimulation of DNA synthesis is the activation of the mitogen-activated protein kinases (MAPKs). The regulation of MAPK activation by the G_i2-coupled thrombin and acetylcholine muscarinic M₂ receptors occurs by a sequential activation of a network of protein kinases. The MAPK kinase (MEK) which phosphorylates and activates MAPK is also activated by phosphorylation. MEK is phosphorylated and activated by either Raf or MEK kinase (MEKK). Thus, Raf and MEKK converge at MEK to regulate MAPK. G_i2-coupled receptors are capable of activating MEK and MAPK by Raf-dependent and Raf-independent mechanisms. Pertussis toxin catalyzed ADP-ribosylation of α_i2 inhibits both the Raf-dependent and-independent pathways activated by G_i2-coupled receptors. The Raf-dependent pathway involves Ras activation, while the Raf-independent activation of MEK and MAPK does not involve Ras. The Raf-independent activation of MEK and MAPK most likely involves the activation of MEKK. The vertebrate MEKK is homologous to the Ste11 and Byr2 protein kinases in the yeast Saccharomyces cerevisiae and Schizosaccharomyces pombe, respectively. The yeast Ste11 and Byr2 protein kinases are involved in signal transduction cascades initiated by pheromone receptors having a 7 membrane spanning serpentine structure coupled to G proteins. MEKK appears to be conserved in the regulation of G protein-coupled signal pathways in yeast and vertebrates. Raf represents a divergence in vertebrates from the yeast pheromone-responsive protein kinase system. Defining MEKK and Raf as a divergence in the MAPK regulatory network provides a mechanism for differential regulation of this system by G_i2-coupled receptors as well as other receptor systems, including the tyrosine kinases.     

Pollination success in a population of dioecious rain forest trees

Pollination success in female trees was determined for a population of Neolitsea dealbata (R. Br.) Merr., a locally abundant dioecious tree pollinated by small, unspecialized insects in northern Queensland rain forest, Australia. The population consisted of a clustered group of trees with a mean male-to-female distance of 4.5 m and more isolated individuals, including females more than 90 m away from the nearest pollen source. A map of all reproductive trees was produced to determine accurate male-to-female distances. The size of the pollen source available to females was defined as a function of the distance to the nearest ten male trees and their sizes (male neighbourhood index). The rate of pollen movement to females was measured by counting pollen tubes (and the number of tubes per style) in female trees 6 days after the commencement of population flowering. The pollination rate decreased steeply to less than half when the nearest male was only 6.5 m away. Although pollen reached a female 330 m away from the nearest pollen source, only 10% of receptive flowers had been pollinated. The short flowering period (2–3 weeks) combined with the the slow rate of pollen movement means that a large proportion of flowers in isolated trees are unpollinated, confirming an earlier finding that isolated females set fewer fruits than gregarious females. The reliability of pollen transfer to females was determined by quantifying insects and their pollen loads trapped at female trees with a range of male neighbourhood indices. Quantities of insects and pollen were significantly correlated with the size of the male neighbourhood index, indicating a strong density-dependent response by vectors to flowering. Pollen was also collected from insect visitors to non-flowering trees. Females with large male neighbourhood indices received more pollen than non-flowering trees with equivalent male neighbourhood indices. However, when the male neighbourhood indices were small for both female and non-flowering trees, the changces of pollinators encountering female and non-flowering trees were similar, suggesting random movements of pollinators in sparse-flowering sub-populations. The dioecious breeding system, brief, synchronous flowering period, clustered population structure and random, opportunistic foraging behaviour of vectors interacted in a way that reduced reproduction in relatively isolated trees. These results demonstrate a mechanism for differential breeding success between trees in natural populations and emphasize the possible impact of logging regimes on pollen flow between trees. Large interconspecific distances in species-rich environments may have been a factor in the selection for synchronous flowering between trees in outcrossing tree species with generalist insect pollinators.     

Temperature and Antarctic plankton community respiration

Antarctic plankton community respiration rates were determinedfrom in vitro changes in dissolved oxygen. Oxygen consumptionrates, measured at in situ temperatures between 0 and 6°C,were found to lie in the range 0.3–3.7 µmol O₂ l^–1per 24 h. Water samples were collected between East FalklandIsland and South Georgia, South Atlantic Ocean, and incubatedshipboard in the dark at up to 36 temperatures between –2and 14–C. A respiration rate at each temperature was thendetermined and used to calculate the temperature coefficient(Q₁₀) of Antarctic planktonic community respiration from theArrhenius equation. Fourteen Q₀ values lay in the range 1–3,with four further values >5. This range of temperature coefficientvalues for community respiration is comparable to the publishedrange of values for plankton photosynthesis. Frequency distributionsof temperature coefficients for the two processes show similarmodal Q₁₀5 of 2–3. Thus, this study does not lend supportto the hypothesis of a differential response of photosynthesisand community respiration to low temperature.     

Measures of food quality as demographic predictors in freshwater copepods

This study examines the ability of a number of short-term measuresof algal food quality to predict longer term demographic parametersfor two species of freshwater calanoid copepods, Diaptomus minuiusand Epischura lacustris. Food quality of two species of algaethat are usually considered highly edible (Cryptomonas erosavar. reflexa and Chlamydomonas reinhardtii) are compared withrespect to: (i) the biochemical constituents of the algae (totalN, total C and protein); (ii) short-term foraging responsesby D.minutus to either algal species (e.g. clearance, ingestionand assimilation rates); (iii) longer term demographic responses(e.g. survivorship and reproduction) by both D.minutus and E.lacustrisfed a diet of either algal species. Demographic responses ofthe two copepod species indicate that C.erosa is a higher qualityfood. In fact, survival and reproduction of both copepod speciesfed C.reinhardtii were not different from starved treatments.Cryptomonas erosa treatments also had greater C, N and protein.However, D.minutus ingested five times more C.reinhardtii thanC.erosa, indicative of ‘compensatory feeding’ inthe presence of poor-quality food. Based upon these higher ingestionrates, individuals fed C.reinhardai actually ingested greateramounts of C, N and protein. Hence, ingestion rates taken aloneor coupled with biochemical parameters are not reliable predictorsof consumer demographic response. Assimilation rate, which waspositive for C.erosa and zero for C.reinhardtii, was the singlebest short-term predictor of food quality.     

鄂东南地区下侏罗统武昌组的双壳类化石

湖北蒲圻车埠和大冶金山店下侏罗统武昌组的双壳类化石可划分为２个组合,武昌组中部Ｑｉｙａｎｇｉａ－Ａｐｓｅｕｄｏｃａｒｄｉｎｉａ组合和武昌组上部Ｈｕｂｅｒｉｃｏｎｃｈａ－Ｋｉｊａ（Ｗｕｃｈａｎｇｅｌｌａ）组合,前者时代为早侏罗世中晚期;后者暂归于早侏罗世最晚期。文中描述２新属１新亚属以及１５新种。     

Effects of Environmental and Nutritional Factors on Production of the Polyketide Phytotoxin Coronatine by Pseudomonas syringae pv. Glycinea

Pseudomonas syringae pv. glycinea PG4180 produces the polyketide phytotoxin coronatine. The effects of environmental, nutritional, and host factors on growth and coronatine production by PG4180 were examined by varying the components of a defined basal medium which contained the following nutrients per liter: glucose (10 g), NH₄Cl (1 g), MgSO₄ · 7H₂O (0.2 g), KH₂PO₄ (4.1 g), K₂HPO₄ · 3H₂O (3.6 g), and FeCl₃ (2 μM). Bacterial growth was recorded as dry weight, and coronatine production was measured by high-performance liquid chromatography. Both growth and the quantity of coronatine synthesized were significantly affected by carbon source, nutrient levels (glucose, NH₄Cl, phosphate, Mg, and SO₄), amino acid supplements, and the presence of complex carbon and nitrogen sources. The yield of coronatine generally declined when conditions were varied from those in the basal medium. Coronatine production and growth were not affected when the pH was adjusted from 6.5 to 7.8. Increases in the osmolarity of the basal medium significantly decreased coronatine production without affecting growth. The addition of plant extracts, plant-derived secondary metabolites, or zinc did not affect growth or coronatine production, while the addition of millimolar levels of KNO₃ or micromolar levels of FeCl₃ significantly enhanced coronatine production. The yield of coronatine was maximized after a 7-day incubation at 18°C and 280 rpm. The results of the present study were used to formulate a medium which allowed for enhanced coronatine production in nearly all strains of P. syringae tested. A rapid method for extracting coronatine from small volumes of culture supernatant was also developed.