C : N : P stoichiometry of dominant riparian trees and arthropods along the Middle Rio Grande

1. We examined the role of flooding on the leaf nutrient content of riparian trees by comparing the carbon : nitrogen : phosphorus (C : N : P) ratio of leaves and litter of Rio Grande cottonwood (Populus deltoides ssp. wislizenii) in flood and non‐flood sites along the Middle Rio Grande, NM, U.S.A. The leaf C : N : P ratio was also examined for two non‐native trees, saltcedar (Tamarix chinensis) and Russian olive (Elaeagnus angustifolia), and six species of dominant riparian arthropods. 2. Living leaves and leaf litter of cottonwoods at flood sites had a significantly lower leaf N : P ratio and higher %P compared with leaves and litter at non‐flood sites. A non‐flood site downstream from wastewater effluent had a significantly lower litter C : N ratio than all other sites, suggesting N fertilisation through ground water. The non‐native trees, saltcedar and Russian olive, had higher mean leaf N content, N : P ratio, and lower C : N ratio compared with cottonwoods across study sites. 3. Riparian arthropods ranged from 5.2 to 7.1 for C : N ratio, 56–216 for C : P ratio, and 8.9–34 for N : P ratio. C content ranged from 25 to 52% of dry mass, N content from 4.7 to 10.8%, and P content from 0.59 to 1.2%. Differences in stoichiometry between high C : nutrient leaf litter and low C : nutrient invertebrates suggests possible food‐quality constraints for detritivores. 4. These results suggest that spatial and temporal variation in the C : N : P ratio of cottonwood leaves and leaf litter is influenced by surface and subsurface hydrologic connection within the floodplain. Reach‐scale variation in the elemental composition of riparian organic matter inputs may have important implications for decomposition, nutrient cycling, and food webs in river floodplain systems.     

Parthenogenetic development of dwarf surf dam,Mulinia lateralis,oocytes treated with polar body suppressing agents

Summary

Parthenogenesis following oocyte activation has been observed in a number of marine invertebrates, but the fate of parthenogenesis in bivalve mollusc embryos is unclear. We used the dwarf surf clam, Mulinia lateralis, to examine parthenogenetic development of KC1-activated oocytes using the polar body suppressing agents caffeine and heat or cytochalasin B. Development was followed by epifluorescence microscopy and flow-cytometric analysis using the DNA-specific fluorochrome DAPI. All agents suppressed polar body formation to some degree, putatively increasing the ploidy level and retaining a meiotic centrosome in the zygote; but the zygotes failed to develop normally. Failure of the zygotes to develop suggests that the meiotic centrosome is incapable of participating in mitosis in bivalves.     

Regulation of maturation-promoting factor by protein kinase C in Chaetopterus oocytes

Summary

We present the results of a variety of studies showing that activation of protein kinase C (PKC) in oocytes of Chaetopterus pergamentaceus results in germinal vesicle breakdown (GVBD). Phorbol esters and diacylglycerol can initiate a morphologically normal GVBD accompanied by a spectrum of associated biochemical processes, including increased protein phosphorylation, a shift in protein synthesis and activation of a protein kinase, maturation promoting factor (MPF). MPF activation is essential for GVBD in response to phorbol esters. In addition, inhibitors of PKC can block naturally-induced GVBD. We also present evidence that PKC can phosphorylate p34^cde2, the catalytic subunit of MPF and that phosphorylation by PKC increases the histone H1 kinase activity of immunoprecipitated MPF. Immunoblot studies show that Chaetopterus oocyte p34^cdc2 is not tyrosine phosphorylated prior to the initiation of GVBD, indicating that activation of MPF at GVBD in this species does not require p80^cdc25, the activator of MPF at mitosis. These results suggest that PKC is an essential regulator of GVBD which can directly phosphorylate and regulate p34^cdc2. Since PKC is the intracellular receptor for and is directly activated by tumor-promoters, tumor promotion might involve acceleration of the cell cycle through modification of the enzymatic activity of MPF by PKC.     

Mosquito and West Nile virus surveillance in northeast Montana,U.S.A., 2005 and 2006

Mosquito and West Nile virus (WNV) surveillance was conducted on a national wildlife refuge in northeast Montana in 2005 and 2006, during which outbreaks of WNV in a colony of American white pelicans (Pelecanus erythrorhynchos Gmelin) (Pelecaniformes: Pelecanidae) resulted in juvenile mortality rates of ～ 31%. Both years, floodwater species Ochlerotatus dorsalis (Meigen) (Diptera: Culicidae), Aedes vexans (Meigen) (Diptera: Culicidae) and Ochlerotatus flavescens (Muller) (Diptera: Culicidae) comprised 78% of the total collection and heightened host‐seeking activity was observed from mid‐June to mid‐July. Culex tarsalis Coquillett (Diptera: Culicidae) was most active from mid‐July to mid‐August and comprised 18% of the collection in 2005 and 20% in 2006. However, fewer than 10% of the Cx. tarsalis females collected in 2006 were obtained adjacent to the pelicans' nesting grounds. Minimum infection rates per 1000 Cx. tarsalis tested for WNV were 1.36 in 2005 and 1.41 in 2006. All pools in which WNV was detected in 2006 were composed of females collected 10 km from the nesting grounds. Substantial juvenile pelican mortality in 2006 despite reductions in the population of the primary vector and in mosquito infection rates near the colony suggests that the methods used to detect the introduction of WNV were too coarse and that amplification of the virus within the colony may reflect causes other than mosquito infection.     

A clinally varying promoter polymorphism associated with adaptive variation in wing size in Drosophila

Body size often shows adaptive clines in many ectotherms across altitude and latitude, but little is known about the genetic basis of these adaptive clines. Here we identify a polymorphism in the Dca (Drosophila cold acclimation) gene in Drosophila melanogaster that influences wing size, affects wing:thorax allometry and also controls a substantial proportion of the clinal wing‐size variation. A polymorphism in the promoter region of Dca had two common alleles showing strong reciprocal clinal variation in frequency with latitude along the east coast of Australia. The Dca‐237 allele increased towards the tropics where wing size is smaller. A within‐population association study highlighted that an increase in the frequency of this allele decreased wing size but did not influence thorax size. A manipulated increase in the level of expression of Dca achieved through UAS‐GAL4 was associated with a decrease in wing size but had no effect on thorax size. This was consistent with higher Dca expression levels in family lines with higher frequency of the Dca‐237 allele. Genetic variation in the promoter region of the Dca gene appears to influence adaptive size variation in the eastern Australian cline of Drosophila melanogaster and accounts for more than 10% of the genetic variation in size within and between populations.     

A New Malaria Parasite Plasmodium (Sauramoeba) heischi in Skinks (Mabuya striata) from Nairobi, with a Brief Discussion of the Distribution of Malaria Parasites in the Family Scincidae

ABSTRACT. A new species of malaria parasite, Plasmodium (Sauramoeba) heischi , is described from African skinks (Mabuya striata). Eleven individuals of 90 specimens collected in Nairobi were found to be infected. The new parasite is a large species, characterized by spindle-shaped gametocytes, the female often with a subterminal nucleus. The schizonts produce up to 65 nuclei and cause great hypertrophy and distortion of the host cell. Although similar to P. (Sauramoeba) giganteum in dimensions and merozoite numbers, P. heischi is easily distinguished by gametocyte and schizont shapes.     

Use of Shields stress to reconstruct and forecast changes in river metabolism

1. Discharge patterns of streams and rivers may be substantially affected by changes in water management, land use, or climate. Such hydrological alterations are likely to influence biotic processes, including overall ecosystem metabolism (photosynthesis and respiration). One regulator of aquatic ecosystem metabolism directly tied to hydrology is movement of bed sediments. 2. We propose that ecosystem metabolism can be reconstructed or predicted for any suite of hydrological conditions through the use of quantitative relationships between discharge, bed movement and metabolism. We tested this concept on a plains reach of the South Platte River in Colorado. 3. Movement of bed sediments was predicted from river discharge and the Shields stress, a ratio of velocity‐induced stress to sediment grain size. Quantitative relationships were established empirically between metabolic response to bed movement and recovery from bed movement, thus linking metabolism to hydrology. 4. The linkage of metabolism to hydrology allowed us to reconstruct daily photosynthesis and respiration over the 70‐year period for which discharge is known at our study site on the South Platte River. The reconstruction shows major ecological change caused by hydrological manipulation: the river has lost two‐thirds of its photosynthetic potential, and the ratio of photosynthesis to respiration is now much lower than it was prior to 1960. 5. The same approach could be used to anticipate ecological responses to proposed hydrological manipulations, to quantify benefits of hydrological restoration, or to illustrate potential effects of change in climate or land use on flowing‐water ecosystems.     

The mechanisms of iron isotope fractionation produced during dissimilatory Fe(III) reduction by Shewanella putrefaciens and Geobacter sulfurreducens

Microbial dissimilatory iron reduction (DIR) is widespread in anaerobic sediments and is a key producer of aqueous Fe(II) in suboxic sediments that contain reactive ferric oxides. Previous studies have shown that DIR produces some of the largest natural fractionations of stable Fe isotopes, although the mechanism of this isotopic fractionation is not yet well understood. Here we compare Fe isotope fractionations produced by similar cultures of Geobacter sulfurreducens strain PCA and Shewanella putrefaciens strain CN32 during reduction of hematite and goethite. Both species produce aqueous Fe(II) that is depleted in the heavy Fe isotopes, as expressed by a decrease in ⁵⁶Fe/⁵⁴Fe ratios or δ⁵⁶Fe values. The low δ⁵⁶Fe values for aqueous Fe(II) produced by DIR reflect isotopic exchange among three Fe inventories: aqueous Fe(II) (Fe(II)_aq), sorbed Fe(II) (Fe(II)_sorb), and a reactive Fe(III) component on the ferric oxide surface (Fe(III)_reac). The fractionation in ⁵⁶Fe/⁵⁴Fe ratios between Fe(II)_aq and Fe(III)_reac was –2.95‰, and this remained constant over the timescales of the experiments (280 d). The Fe(II)_aq – Fe(III)_reac fractionation was independent of the ferric Fe substrate (hematite or goethite) and bacterial species, indicating a common mechanism for Fe isotope fractionation during DIR. Moreover, the Fe(II)_aq – Fe(III)_reac fractionation in ⁵⁶Fe/⁵⁴Fe ratios during DIR is identical within error of the equilibrium Fe(II)_aq – ferric oxide fractionation in abiological systems at room temperatures. This suggests that the role of bacteria in producing Fe isotope fractionations during DIR lies in catalyzing coupled atom and electron exchange between Fe(II)_aq and Fe(III)_reac so that equilibrium Fe isotope partitioning occurs. Although Fe isotope fractionation between Fe(II)_aq and Fe(III)_reac remained constant, the absolute δ⁵⁶Fe values for Fe(II)_aq varied as a function of the relative proportions of Fe(II)_aq, Fe(II)_sorb, and Fe(III)_reac during reduction. The temporal variations in these proportions were unique to hematite or goethite but independent of bacterial species. In the case of hematite reduction, the small measured Fe(II)_aq – Fe(II)_sorb fractionation of −0.30‰ in ⁵⁶Fe/⁵⁴Fe ratios, combined with the small proportion of Fe(II)_sorb, produced insignificant (<0.05‰) isotopic effects due to sorption of Fe(II). Sorption of Fe(II) produced small, but significant effects during reduction of goethite, reflecting the higher proportion of Fe(II)_sorb and larger measured Fe(II)_aq – Fe(II)_sorb fractionation of –0.87‰ in ⁵⁶Fe/⁵⁴Fe ratios for goethite. The isotopic effects of sorption on the δ⁵⁶Fe values for Fe(II)_aq were largest during the initial stages of reduction when Fe(II)_sorb was the major ferrous Fe species during goethite reduction, on the order of 0.3 to 0.4‰. With continued reduction, however, the isotopic effects of sorption decreased to <0.2‰. These results provide insight into the mechanisms that produce Fe isotope fractionation during DIR, and form the basis for interpretation of Fe isotope variations in modern and ancient natural systems where DIR may have driven Fe cycling.     

Do invasive ants respond more strongly to carbohydrate availability than co‐occurring non‐invasive ants? A test along an active Anoplolepis gracilipes invasion front

Invasions by non‐native insects can have important ecological impacts, particularly on island ecosystems. However, the factors that promote the success of invaders relative to co‐occurring non‐invasive species remain unresolved. For invasive ants, access to carbohydrate resources via interactions with both extrafloral nectary‐bearing plants and honeydew‐excreting insects may accelerate the invasion process. A first step towards testing this hypothesis is to determine whether invasive ants respond to variation in the availability of carbohydrate resources, and whether this response differs from that of co‐occurring, non‐invasive ants. We investigated the effect of carbohydrate subsidies on the short‐term foraging and hemipteran‐tending behaviours of the invasive ant Anoplolepis gracilipes (Formicidae) and co‐occurring ant species on an extrafloral nectary‐bearing plant by experimentally manipulating carbohydrate levels and tracking ant recruitment. We conducted experiments in 2 years at two sites: one site was invaded by A. gracilipes prior to 2007 and the other became invaded during the course of our study, allowing pre‐ (2007) and post‐invasion (2009) comparisons. Short‐term increases in carbohydrate availability increased the density of A. gracilipes workers on plants by as much as 400% and reduced tending of honeydew‐excreting insects by this species by up to 89%, with similar responses across years. In contrast, ants at the uninvaded site in 2007 showed a weak and non‐significant forager recruitment response. Across all sites, A. gracilipes workers were the only ants that responded to carbohydrate manipulations in 2009. Furthermore, ant–carbohydrate dynamics at a site newly invaded by A. gracilipes quickly diverged from dynamics at uninvaded sites and converged on those of the site with an established invasion. These findings suggest that carbohydrate resources may be particularly important for A. gracilipes invasions, and underscore the importance of species interactions, particularly putative mutualisms, in facilitating exotic species invasions.