Sperm chemotaxis in the hydromedusae. II. Some chemical properties of the sperm attractants

Gel filtration on highly cross-linked molecular sieves of the sperm attractants of some hydromedusae revealed that the active agents differ in their molecular weights. These differences fall roughly along taxonomic lines, at least at the order level. Anthomedusae have attractants with molecular weights greater than 5,000, while the Leptomedusae attractants have weights less than 1,000. The Limnomedusae and Trachymedusae attractants have weights above 5,000. All the attractants are heat-stable, but only those of the Leptomedusae can pass across a dialysis membrane with a molecular weight cut-off of 14,000.     

Widespread mass mortalities of the green sea urchin in Nova Scotia,Canada

Mass mortalities of sea urchins exceeding 84 000 t live weight or 2 900 t organic weight occurred during the autumns of 1980 and 1981 along the southern coast of Nova Scotia, Canada. The kill was nearly complete along 160 km of shoreline (straight-line distance) and was inter-mittent along another 280 km. Sea urchins in a variety of rocky habitats were affected, including areas exposed to and sheltered from ocean swell, with both dense and no macrophyte cover, and from 0–13 m depth. The cause of the mortalities was presumed to be a biological agent and was transferable in the laboratory. Colonization of the habitat by subtidal macroalgae and a subsequent large increase in benthic primary production is expected to follow.     

Dynamics of prion disease transmission in mule deer.

Chronic wasting disease (CWD), a contagious prion disease of the deer family, has the potential to severely harm deer populations and disrupt ecosystems where deer occur in abundance. Consequently, understanding the dynamics of this emerging infectious disease, and particularly the dynamics of its transmission, has emerged as an important challenge for contemporary ecologists and wildlife managers. Although CWD is contagious among deer, the relative importance of pathways for its transmission remains unclear. We developed seven competing models, and then used data from two CWD outbreaks in captive mule deer and model selection to compare them. We found that models portraying indirect transmission through the environment had 3.8 times more support in the data than models representing transmission by direct contact between infected and susceptible deer. Model-averaged estimates of the basic reproductive number (R0) were 1.3 or greater, indicating likely local persistence of CWD in natural populations under conditions resembling those we studied. Our findings demonstrate the apparent importance of indirect, environmental transmission in CWD and the challenges this presents for controlling the disease.     

Timing of sperm shedding and release of aggregates in the salp Thalia democratica (Urochordata: Thaliacea)

Many holoplanktonic forms, such as medusae, spawn in response to environmental cues such as light or temperature. Few observations of the time of reproduction have been made in salps. Small groups of mature aggregates of the salp Thalia democratica (Forskal, 1775), collected off the Great Barrier Reef of Australia, were held under constant light in early to mid-December in the years 1990, 1993 and 1994. Sperm were shed between 0300 and 0600 hrs each day with a mean time of about 0450 hrs for all individuals for all years combined. Solitary stages released chains of fertilizable female individuals between 0500 and 0700 hrs each day, with a mean time of 0540 hrs. Field observations suggested that similar timing occurred in nature. Advancing the time of dusk from 1900 to 1700 or 1800 hrs. did not significantly alter the mean time of sperm shedding or chain release. T. democratica aggregates, collected in the Mediterranean Sea in 1995 and maintained in constant light, had a broader distribution of individual spawning times, with a mean time of 0625 hrs, which differed significantly from that of the Australian population. Coordination of the events of sexual reproduction in T. democratica may improve fertilization success and be responsible for recognizable age cohorts within blooms of this species. Received: 27 May 1997 / Accepted: 20 June 1997     

Sperm chemotaxis in the hydromedusae. I. Species-specificity and sperm behavior

Egg extracts from 32 species of marine hydromedusae, siphonophores and sessile hydroids were tested for sperm attracting activity using the sperm of all species in both homo- and heterospecific combinations. Species-specific sperm chemotaxis could be demonstrated in nearly every species tested. Of the 1,024 possible combinations, 272 could not be attempted for lack of material. Of the 752 which were carried out, only 13 heterospecific cross-reactions were found. The bulk of these involved reactions which were either weaker in the heterospecific direction or unidirectional. The sperm behavior in response to both homospecific and heterospecific egg extracts is described. In the latter case, no changes in sperm motility or direction of movement were observed. In the former case, the sperm show turning behavior which brings them closer to the source of the extract. Since most of the Hydrozoa tested share the same habitat and are reproductively active at the same time of year, it appears that species-specific sperm chemotaxis may be a significant mechanism for both ensuring fertilization in an environment which subjects the gametes to massive dilution and preventing hybridization.     

Effects of rhizobium, arbuscular mycorrhizal fungi and anion content of simulated rain on subterranean clover

An experiment was conducted to determine the extent to which rhizobia, mycorrhizal fungi, and anions in simulated rain affect plant growth response to acid deposition. Germinating subterranean clover seeds were planted in steam-pasteurized soil in pots and inoculated with Rhizobium leguminosarum, Glomus intraradices, Glomus etunicatum, R. leguminosarum + G. intraradices, R. leguminosarum + G. etunicatum, or no microbial symbionts. Beginning 3 weeks later, plants and the soil surface were exposed to simulated rain in a greenhouse on 3 days week(-1) for 12 weeks. Rain solutions were deionized water amended with background ions only (pH 5.0) or also adjusted to pH 3.0 with HNO3 only, H2SO4 only, or a 50/50 mixture of the two acids. Glomus intraradices colonized plant roots poorly, and G. intraradices-inoculated plants responded like nonmycorrhizal plants to rhizobia and rain treatments. Variation in plant biomass attributable to different rain formulations was strongest for G. etunicatum-inoculated plants, and the effect of rain formulation differed with respect to nodulation by rhizobia. The smallest plants at the end of the experiment were noninoculated plants exposed to rains (0.38 g mean dry weight total for 3 plants pot(-1)). Among nonnodulated plants infected by G. etunicatum, those exposed to HNO3 rain were largest, followed by plants exposed to HNO3 + H2SO4, pH 5.0, and H2SO4 rain, in that order. Among plants inoculated with both R. leguminosarum + G. etunicatum, however, the greatest biomass occurred with pH 5.0 rains, resulting in the largest plants in the study (1.00 g/3 plants). Treatment-related variation among root and shoot biomass data reflected those for whole-plant biomass. Based on quantification of biomass and N concentrations in shoot and root tissues, total N content of plants inoculated with G. etunicatum alone and exposed to the HNO3 + H2SO4 rains was approximately the same as plants inoculated with R. leguminosarum + G. entunicatum and exposed to pH 5 rains. Thus, the acid-mixture rains and rhizobia under no acid deposition provided approximately equal amounts of N in biomass. The significant interactions among rain formulation and the symbiotic status of the plants suggest that conclusions concerning the impact of acid deposition on plants in the environment cannot be considered reliable because most experiments on which such assessments are based have not tested confounding influences of microorganisms and precipitation characteristics.     

An environmental decision-making tool for evaluating ground-level ozone-related health effects

A computer model called the Ozone Risk Assessment Model (ORAM) was developed to evaluate the health effects caused by ground-level ozone (O3) exposure. ORAM was coupled with the U.S. Environmental Protection Agency's (EPA) Third-Generation Community Multiscale Air Quality model (Models-3/CMAQ), the state-of-the-art air quality model that predicts O3 concentration and allows the examination of various scenarios in which emission rates of O3 precursors (basically, oxides of nitrogen [NOx] and volatile organic compounds) are varied. The principal analyses in ORAM are exposure model performance evaluation, health-effects calculations (expected number of respiratory hospital admissions), economic valuation, and sensitivity and uncertainty analysis through a Monte Carlo simulation. As a demonstration of the system, ORAM was applied to the eastern Tennessee region, and the entire O3 season was simulated for a base case (typical emissions) and three different emission scenarios. The results indicated that a synergism occurs when reductions in NOx emissions from mobile and point sources were applied simultaneously. A 12.9% reduction in asthma hospital admissions is expected when both mobile and point source NOx emissions are reduced (50 and 70%, respectively) versus a 5.8% reduction caused by mobile source and a 3.5% reduction caused by point sources when these emission sources are reduced individually.     

Airborne observations of vegetation and implications for biogenic emission characterization

Measuring hydrocarbons from aircraft represents one way to infer biogenic emissions at the surface. The focus of this paper is to show that complementary remote sensing information can be provided by optical measurements of a vegetation index, which is readily measured with high temporal coverage using reflectance data. We examine the similarities between the vegetation index and in situ measurements of the chemicals isoprene, methacrolein, and alpha-pinene to estimate whether the temporal behavior of the in situ measurements of these chemicals could be better understood by the addition of the vegetation index. Data were compared for flights conducted around Houston in August and September 2000. The three independent sets of chemical measurements examined correspond reasonably well with the vegetation index curves for the majority of flight days. While low values of the vegetation index always correspond to low values of the in situ chemical measurements, high values of the index correspond to both high and low values of the chemical measurements. In this sense it represents an upper limit when compared with in situ data (assuming the calibration constant is adequately chosen). This result suggests that while the vegetation index cannot represent a purely predictive quantity for the in situ measurements, it represents a complementary measurement that can be useful in understanding comparisons of various in situ observations, particularly when these observations occur with relatively low temporal frequency. In situ isoprene measurements and the vegetation index were also compared to an isoprene emission inventory to provide additional insight on broad issues relating to the use of vegetation indices in emission database development.     

Solubilities of hydrophobic compounds in aqueous-organic solvent mixtures

Solubilities of several hydrophobic organic substances (paradichlorobenzene, endrin, naphthalene, and dibutyl phthalate) in aqueous solutions containing up to 0.10 mole fraction of common alcohols and ketones, were measured by gas chromatography. The solubilities are significantly increased by the alcohols and ketones. The results are interpreted in terms of the association of n molecules of alcohol or ketone with each hydrophobic organic molecule. Values of n and the equilibrium constant for this association are reported for each hydrophobic organic-alcohol and organic-ketone combination. The implications of these results for the disposal of toxic wastes by landfilling is discussed.     

An approach to the assessment of the quality of environmental monitoring data

This paper reports an approach to the assessment of the validity of environmental monitoring data--a 'data filter'. The strategy has been developed through the UK National Marine Analytical Quality Control (AQC) Scheme for application to data collected for the UK National Marine Monitoring Plan, although the principles described are applicable more widely. The proposed data filter is divided into three components: Part A, 'QA/QC'--an assessment of the laboratory's practices in Quality Assurance/Quality Control; Part B, 'fitness for purpose'--an evaluation of the standard of accuracy that can be demonstrated by activities in (A), in relation to the intended application of the data; and Part C, the overall assessment on which data will be accepted as usable or rejected as being of suspect quality. A pilot application of the proposed approach is reported. The approach described in this paper is intended to formalise the assessment of environmental monitoring data for fitness for a chosen purpose. The issues important to fitness for purpose are discussed and assigned a relative priority order on which to judge the reliability/usefulness of monitoring data.