Variation in Outcrossing Rates in Eichhornia paniculata: Temporal Changes in Populations of Contrasting Style Morph Structure

Abstract Surveys of mating-system parameters in populations of the annual, self-compatible, tristylous, emergent aquatic, Eichhornia paniculata (Pontederiaceae) from N.E. Brazil and Jamaica have indicated that the species exhibits a wide range of outcrossing rates. To investigate whether temporal variation in outcrossing rate was also a feature of populations, open-pollinated families were sampled from five populations of contrasting style morph structure from N.E. Brazil over three consecutive years (1987–1989). Multilocus estimates of outcrossing rate ( t ) were obtained from assays of isozyme polymorphisms using starch gel electrophoresis. There was significant variation both among populations and between years in the frequency of outcrossing. Outcrossing in three tristylous populations was high ( t > 0.80), with relatively small fluctuations occurring over the three-year sampling period. In contrast, in a dimorphic and monomorphic population considerable self-fertilization occurred and the frequency of outcrossing declined significantly from 1987 to 1989 in both populations. In the dimorphic population, increased selfing was associated with a marked reduction in population size and an increase in the frequency of selfing variants of the mid-styled morph. The significance of temporal variation in outcrossing frequency in plant populations is discussed in relation to its effect on population genetic structure and recent models of mating-system evolution.     

Influence of ultraviolet-B radiation on the drift response of stream invertebrates

1. Recent studies have shown that ultraviolet (UV) radiation (280–400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet-B (UVB; 280–320 nm) radiation on the drift response of immature stream insects in laboratory microcosms.
2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid-day conditions at Fort Collins, Colorado (longitude 105°30'; latitude 40°35').
3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB-exposed streams may be a behavioural response and/or a result of injury.
4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats.     

The energetic importance of terrestrial arthropod inputs to three warm-water streams

1. Inputs of terrestrial arthropods (number and mass m^–2 d^–1) from riparian corridors to three streams representing different orders were highly variable among seasons and sites, with significantly greater ( P < 0.05) inputs at the headwater stream during summer months, compared with other sites and seasons.
2. No significant differences in estimates of stream retention of terrestrial arthropods (number and mass m^–2 d^–1) were observed among sites; however, retention of terrestrial arthropods at all sites was significantly greater during summer months, compared with other periods.
3. The gravimetric proportion of terrestrial arthropods present in the stomachs of redbreast sunfish ( Lepomis auritus ) and bluegill ( L. macrochirus ) was equivalent among sites. However, estimates of the dietary importance of terrestrial arthropods at all study sites were significantly greater in the summer, compared with other seasons.
4. Estimates of the potential annual energetic contribution (kJ m^–2 d^–1) of terrestrial arthropod inputs to the stream system were comparable with published rates of total annual production of aquatic macroinvertebrates in other Virginia headwater streams.
5. Results of this study supported the hypothesis that terrestrial arthropods represented an important energetic subsidy to stream fish during periods of low aquatic macroinvertebrate availability, and suggest that this component of allochthonous input is a potentially significant, but poorly understood energetic linkage between riparian landscapes and stream ecosystems.     

Microsporidian Spore Discharge and the Transfer of Polaroplast Organelle Membrane into Plasma Membrane

Electron microscopic examinations of Glugea hertwigi and Spraguea lophii spores indicated the presence of a single plasma membrane; however, this membrane remained in the spore during the discharge of the sporoplasm from the spore. Although discharged spores retained the old plasma membrane, the extruded sporoplasms acquired a new plasma membrane. In order to determine where the new plasma membrane came from, we used two fluorescent probes with membrane affinities. The markers were tested on unfired and discharged spores. The probe, N-phenyl-1-naphthylamine (NPN), labeled the polaroplast membrane in addition to the apolar groups in the posterior vacuoles of unfired spores. After spore discharge, NPN label disappeared from the spore ghosts except for a slight fluorescence on residual plasma membranes. Much of the NPN-labeled membrane reappeared after spore discharge on the outer envelope of discharged sporoplasms. The probe chlorotetracycline (CTC) labeled calcium-associated membranes of spore polaroplasts. During spore discharge, the CTC fluorescence shifted from the polaroplast organelle of unfired spores to the outer envelope of discharged sporoplasms. These results indicate that the polaroplast organelle may provide the new plasma membrane for discharged microsporidian sporoplasms.     

Electrical Polarity and Cellular Differentiation in Meroistic Ovaries

SYNOPSIS. In the oocyte-nurse cell syncytium of meroistic insectovaries a gradient in electrical potential is shown to drivea micro-injected basic protein (fluorescein-labeled lysozyme)and its methylcarboxylated, acidic derivative in opposite directions.In the polytrophic Cecropia ovary the electrophoretic effectis greatest in the intercellular bridges, while in the telotrophicRhodnius ovary it is greatest within the nurse chamber. We speculatethat in both systems the potential gradient prevents the freediffusion of cell cycle and differentiative control proteins,while at the same time reinforcing the transport of acidic precursorstoward the ooplasm. Because of its apparent ability to affectthe distribution of polyions that govern nuclear function, electricalpolarity can also be envisioned to have a more general rolein the control of differentiation. The possibility is consideredthat it serves as a relay mechanism for the non-diffusing determinantthat is already known to govern the differentiation of oocytesfrom nurse cells.     

Effect of Galactose and Other Monosaccharides on IAA Movement in Bean Hypocotyl Segments

Galactose enhances the production of ethylene gas, and ethylene gas inhibits the movement of IAA in plant tissues. If galactose enhances ethylene production and ethylene inhibits auxin movement, then galactose should inhibit auxin movement. The above hypothesis was examined by observing the effects of d -galactose, d -inannose, d -arabinose, d -glucose, and d xylose on the uptake, presumed decarboxylation, efflux, velocity and metabolism of labeled indole-3-aectic acid in hypocotyl segments of Phaseolus vulgaris L. cv. Pinto. Galactose inhibited, arabinose and glucose enhanced, and mannose and xylose had no effect on partitioning of auxin between tissue and receptor. The reduction of auxin efflux by galactose was related to an increased presumed decarboxylation, reduced uptake and slower velocity of applied auxin. The relationship between galactose-induced growth effects, ethylene production, and auxin migration are discussed.     

Regulation of Internodal Extension in Avena Shoots by the Inflorescence, Nodes, Leaves, and Intercalary Meristem

It has been found in recent studies that the inflorescence and nodes (node-pulvini) are the primary sources for native gibberellins in the Avena shoot, and that GA₃ is the predominant gibberellin in the inflorescence. In the present work, linear growth of next-to-last internode is drastically reduced by removal of the inflorescence and last leaf. This growth is completely abolished when the nodes are also excised. It is restored fully by the addition of GA₃ when the nodes are present, and restored only partially when the nodes are deleted. Internodal growth in Avena stem segments with basal node present is also restored by native GA₃-like substances extracted from Avena inflorescences and partially purified by silica gel partition column chromatography. Evidence from these studies, taken in toto, indicates that the inflorescence, nodes, and leaves supply gibberellins, leaves supply substrate, and nodes modulate the gibberellin growth response in next-to-last Avena internodes.     

Nosema parkeri sp. n., a Microsporidan from the Argasid Tick, Ornithodoros parkeri Cooley

SYNOPSIS. Nosema parkeri sp. n. is described from nymphs and adults of the argasid tick, Ornithodoros parkeri Cooley, from a laboratory colony. Schizogonic and sporogonic stages are described from various tick tissues. Spores are binucleate, measuring 3.2 (3–4) × 1.9 (1.8–2.5) μm. Transmission is transovarial and transstadial. The parasite does not appear to affect adversely the development or reproduction of the tick. Dermacentor andersoni Stiles was experimentally infected. Attempts to infect Swiss mice by tick feeding or by injection of infected tick suspensions were unsuccessful. The microsporidan differs in structure from Encephalitozoon ixodis Weiser) and Nosema slovaca Weiser & Reháček, the only other microsporidans known from ticks.     

Inhibition of Nitrate Assimilation in Roots in the Presence of Ammonium: The Moderating Influence of Potassium

Experiments were conducted to investigate the effect of concentrationof NH₄⁺ in nutrient solution on root assimilation of NO₃^–and to determine whether the NH₄⁺NO₃^– interaction wasmodified in the presence of K⁺. Dark-grown, detopped corn seedlings(cv. Pioneer 3369A) were exposed for 8 h to 0.15 mM Ca(NO₃)₂and varying concentrations of (NH₄)₂SO₄ in the absence or presenceof 0.15 mM K₂SO₄. The accelerated phase of NO₃^– uptakeappeared most sensitive to restriction by additions of 0.15mM (NH₄)₂SO₄. In the absence of K⁺, the restriction increasedonly slightly even when solution (NH₄)₂SO₄, was increased from0.15 mM to 12.5 mM which was accompanied by an increase of NH₄⁺in the tissue from about 7.0 to 35 µmol g^–1 fr.wt. of root. Increasing concentrations of solution NH₄⁺ progressivelyinhibited net K+ uptake. At the highest solution NH₄⁺ concentrations,there was an initial net efflux of K⁺ and no net influx occurredduring the treatment period. The severity of the NH₄)SO₄ restrictionof NO₃^– uptake was moderated considerably in the presenceof K⁺ as long as a net influx of K⁺ occurred. However, net influxof K⁺ was not associated with alteration of NH₄⁺ uptake, assimilation,or accumulation in the root tissue. The lack of correlationbetween the severity of restriction of NO₃^– uptake andendogenous NHJ suggested the restriction resulted from an effectexerted by exogenous NH₄⁺ which tended to saturate at lowersolution NHJ concentrations or by inhibitory factors generatedduring assimilation of NH₄⁺. Several mechanisms were postulatedto account for the moderating influence of K⁺. In all experiments,root NO₃^– reduction was restricted by the presence ofambient NH₄⁺. The quantitative decreases in reduction tendedto be less than decreases in NO₃^– uptake and therefore,could result from inhibition solely of uptake with subsequentlimitation in availability of substrate for the reduction process,but the possibility of a direct effect on reduction could notbe excluded.