Summer Experiment Research Articles

Litter decomposition in a Cerrado savannah stream is retarded by leaf toughness, low dissolved nutrients and a low density of shredders

Summary1. To assess whether the reported slow breakdown of litter in tropical Cerrado streams is due to local environmental conditions or to the intrinsic leaf characteristics of local plant species, we compared the breakdown of leaves from Protium brasiliense, a riparian species of Cerrado (Brazilian savannah), in a local and a temperate stream. The experiment was carried out at the time of the highest litter fall in the two locations. An additional summer experiment was conducted in the temperate stream to provide for similar temperature conditions.2. The breakdown rates (k) of P. brasiliense leaves in the tropical Cerrado stream ranged from 0.0001 to 0.0008 day−1 and are among the slowest reported. They were significantly (F = 20.12, P < 0.05) lower than in the temperate stream (0.0046–0.0055). The maximum ergosterol content in decomposing leaves in the tropical Cerrado stream was 106 μg g−1, (1.9% of leaf mass) measured by day 75, which was lower than in the temperate stream where maximum ergosterol content of 522 μg g−1 (9.5% of leaf mass) was achieved by day 30. The ATP content, as an indicator of total microbial biomass, was up to four times higher in the tropical Cerrado than in the temperate stream (194.0 versus 49.4 nmoles g−1).3. Unlike in the temperate stream, leaves in the tropical Cerrado were not colonised by shredder invertebrates. However, in none of the experiments did leaves exposed (coarse mesh bags) and unexposed (fine mesh bags) to invertebrates differ in breakdown rates (F = 1.15, P > 0.05), indicating that invertebrates were unable to feed on decomposing P. brasiliense leaves.4. We conclude that the slow breakdown of P. brasiliense leaves in the tropical Cerrado stream was because of the low nutrient content in the water, particularly nitrate (0.05 mgN L−1), which slows down fungal activity and to the low density of invertebrates capable of using these hard leaves as an energy source.

Changes in Vegetation Condition and Surface Fluxes during NAME 2004

Abstract The vegetation in the core region of the North American monsoon (NAM) system changes dramatically after the onset of the summer rains so that large changes may be expected in the surface fluxes of radiation, heat, and moisture. Most of this region lies in the rugged terrain of western Mexico and very few measurements of these fluxes have been made in the past. Surface energy balance measurements were made at seven sites in Sonora, Mexico, and Arizona during the intensive observation period (IOP) of the North American Monsoon Experiment (NAME) in summer 2004 to better understand how land surface vegetation change alters energy flux partitioning. Satellite data were used to obtain time series for vegetation indices and land surface temperature for these sites. The results were analyzed to contrast conditions before the onset of the monsoon with those afterward. As expected, precipitation during the 2004 monsoon was highly variable from site to site, but it fell in greater quantities at the more southern sites. Likewise, large changes in the vegetation index were observed, especially for the subtropical sites in Sonora. However, the changes in the broadband albedo were very small, which was rather surprising. The surface net radiation was consistent with the previous observations, being largest for surfaces that are transpiring and cool, and smallest for surfaces that are dry and hot. The largest evaporation rates were observed for the subtropical forest and riparian vegetation sites. The evaporative fraction for the forest site was highly correlated with its vegetation index, except during the dry spell in August. This period was clearly detected in the land surface temperature data, which rose steadily in this period to a maximum at its end.

Influence of Exogenous Triiodothyronine (T3) on Fecal Shedding of Escherichia coli O157 in Cattle

Fecal prevalence of Escherichia coli O157 in ruminants is highest in the summer months and decreases to low or undetectable levels in the winter. We hypothesize that the seasonal variation of this pathogen is a result of physiological responses within the host animal to changing day length. The thyroid is an endocrine gland known to respond to changing day length. Two experiments were conducted to determine if a hyperthyroid status would initiate fecal shedding of E. coli O157 in cattle during the winter when shedding is virtually nonexistent (winter experiment) or influence cattle actively shedding E. coli O157 (summer experiment). Yearling cattle were group-penned under dry-lot conditions, adjusted to a high concentrate ration, and randomly assigned to treatment: control (1 mL corn oil injected s.c. daily) or triiodothyronine (T(3); 1.5 mg suspended in corn oil injected s.c daily). Cattle were individually processed daily for collection of fecal and blood samples. Treatment with exogenous T(3) produced a significant change in serum thyroid hormone concentrations indicative of a hyperthyroid status in both experiments. No differences (P>0.10) were observed in fecal shedding of E. coli O157 in the winter experiment. In the summer experiment, fecal shedding of E. coli O157 was decreased (P=0.05) by administration of T(3) during the treatment period (days 1-10), tended to be lower (P=0.08) during the following 7-day period of no treatment, and was lower (P=0.01) when examined across the entire experimental period. Results of this research indicate that the thyroid or its hormones may be involved in the seasonal shedding patterns of E. coli O157 in cattle.

The effects of amount, timing and distribution of simulated rainfall on the development of Haemonchus contortus to the infective larval stage

Three studies were undertaken to determine the effects of amount, timing and distribution of simulated rainfall on the developmental success of Haemonchus contortus. Faeces containing H. contortus eggs were deposited onto pasture plots under a rainfall-activated retractable roof which eliminated incident rainfall. In October (spring) 2004 and January (summer) 2005, the effects of amount (6, 12, 18 or 24 mm) and timing (1, 4, 8 or 15 days post-faecal deposition) of a single simulated rainfall event was investigated via manual application of water to plots. More H. contortus pre-infective larvae (L1 and L2) developed under the d 1 simulated rainfall treatment than later treatments. There was no effect of rainfall amount on development in either experiment, and negligible development to infective larvae (L3). In February (summer) 2006, the effects of amount (12, 24 or 32 mm) and distribution (single event or three smaller but equal split events over 32 h) of simulated rainfall events was investigated with water applied via sprinkler. In this experiment L3 were recovered from the herbage in one-third of the plots harvested, however recovery was low (0.08% of eggs deposited) and there were no treatment effects. Recovery of L1 and L2 from faeces increased with simulated rainfall amount at d 4, and more L1 and L2 were recovered from the split distribution treatment at d 4. The results indicate that moisture conditions soon after faecal deposition are key determinants of H. contortus development success, with significant penalties on development when simulated rainfall was applied 7 days or more post-deposition, and when the duration of simulated rainfall was short. High rates of evaporation during both summer experiments resulted in rapid drying of the micro-environment and this appears to have limited development to L3.

Effect of outdoor conditions on growth rate and chemical composition of Gelidium crinale in culture

A comprehensive study of the major environmental factors affecting growth and chemical composition of Gelidium crinale is presented here for the first time. The purpose of this study was to analyze the significance of the major growth factors and to formulate them into regression models. For this purpose summer and winter experiments were conducted in small aerated seawater tanks under various light and fertilizer conditions. The effects of carbon source, pH control and microelements were also tested. Finally, an annual growth experiment was conducted in order to support the two-season experiment. The major limiting seasonal factor was found to be temperature, which positively affected weekly growth rate, dry weight and gel strength, while negatively affecting the agar percentage. Ammonium was also revealed as a major limiting factor, positively affecting chlorophyll and protein concentrations, and negatively affecting carbohydrate concentration. Other growth factors, such as light intensity, pH, carbon source and microelements, were less- or non-effective, being already almost optimal under ambient conditions.

Habitat‐Specific Growth in Juvenile Pinfish

AbstractUnderstanding how certain fish species utilize estuarine habitats is critical for future conservation and management efforts. Habitats with various types of structure, including seagrass, marsh, oyster reef, and nonvegetated bottom, provide transient juvenile fishes with food and refuge from predation. Relative growth rates and survival of species like the pinfish Lagodon rhomboides should depend on the distribution and relative abundance of such habitats within and among bay systems. In many bays, marsh makes up a larger proportion of habitat area than the more often‐studied seagrass, but habitat‐specific comparisons of fish growth have rarely included marsh. Using field enclosures, we compared relative growth of juvenile pinfish in marsh, oyster, and nonvegetated bottom habitats in Grand Bay National Estuarine Research Reserve, Mississippi. Mean growth rates of pinfish juveniles in two summer experiments were 0.39, 0.20, and 0.04 mm/d in marsh, oyster, and nonvegetated bottom habitats, respectively. Growth in marsh habitat was significantly higher than growth in oyster and nonvegetated bottom habitats and was consistent across the two summers of our experiments. From available literature, juvenile pinfish densities are consistently higher in vegetated habitats (marsh and seagrass) than in nonvegetated habitats. Our results indicate that marsh habitat may also provide better foraging options for juvenile pinfish. When combined with evidence from other studies, our results suggest that marsh habitat provides a critical nursery function for juvenile pinfish, especially in estuaries such as Grand Bay, where seagrass habitat is limited.

Sunlight inactivation of Campylobacter jejuni and Salmonella enterica, compared with Escherichia coli, in seawater and river water

The inactivation of Campylobacter jejuni and Salmonella enterica, compared with Escherichia coli, was determined in 100 l chambers of seawater and river water located at an outdoor site. The chambers (paired with dark controls) were seeded with waste stabilization pond effluent and laboratory-cultured pathogens, and exposed to sunlight in summer and winter experiments. All sunlight inactivation (k(S)) rates, as a function of cumulative global solar radiation (insolation), were far higher than the corresponding dark (k(D)) rates, with a ranking (and average k(S) rates for seawater and river water, respectively) of: C. jejuni (3.23; 2.34)>S. enterica (0.51; 0.37)>E. coli (0.34; 0.26). All the T(90) (time to 90% inactivation) values were higher in winter than in summer, but there was far greater similarity between the summer and winter S(90) (insolation needed for 90% inactivation) values. The rapid inactivation of C. jejuni was attributed to a high susceptibility to photooxidative damage. The results suggest that, in sunlight-exposed waters, E. coli will be a more conservative indicator for C. jejuni than for S. enterica, and C. jejuni transmission as a pathogenic agent is less likely than for S. enterica.

Human trampling as short-term disturbance on intertidal mudflats: effects on macrofauna biodiversity and population dynamics of bivalves.

The effect of physical disturbance in the form of trampling on the benthic environment of an intertidal mudflat was investigated. Intense trampling was created as unintended side-effect by benthic ecologists during field experiments in spring and summer 2005, when a mid-shore area of 25 × 25 m was visited twice per month by on average five researchers for a period of 8 months. At the putatively-impacted location (I) (25 × 25 m) and two nearby control locations (Cs) (25 × 25 m each), three sites (4 × 4 m) were randomly selected and at each site, three plots (50 × 50 cm) were sampled after 18 and 40 days from the end of the disturbance. Multivariate and univariate asymmetrical analyses tested for changes in the macrofaunal assemblage, biomass of microphytobenthos and various sediment properties (grain-size, water content, NH4 and NO3 concentrations in the pore water) between the two control locations (Cs) and the putatively-impacted location (I). There were no detectable changes in the sediment properties and microphytobenthos biomass, but variability at small scale was observed. Microphytobenthos and NH4 were correlated at I to the number of footprints, as estimated by the percentage cover of physical depressions. This indicated that trampling could have an impact at small scales, but more investigation is needed. Trampling, instead, clearly modified the abundance and population dynamics of the clam Macoma balthica (L.) and the cockle Cerastoderma edule (L.). There was a negative impact on adults of both species, probably because footsteps directly killed or buried the animals, provoking asphyxia. Conversely, trampling indirectly enhanced recruitment rate of M. balthica, while small-sized C. edule did not react to the trampling. It was likely that small animals could recover more quickly because trampling occurred during the growing season and there was a continuous supply of larvae and juveniles. In addition, trampling might have weakened negative adult-juvenile interactions between adult cockles and juvenile M. balthica, thus facilitating the recruitment. Our findings indicated that human trampling is a relevant source of disturbance for the conservation and management of mudflats. During the growing season recovery can be fast, but in the long-term it might lead towards the dominance of M. balthica to the cost of C. edule, thereby affecting ecosystem functioning.

Elevated temperature and light enhance progression and spread of black band disease on staghorn corals of the Great Barrier Reef

Rates of progression and transmission of black band disease (BBD) on the staghorn coral, Acropora muricata, were compared between months for seasonal in situ studies and between temperature treatments in experimental aquaria manipulations at Lizard Island on the Great Barrier Reef (GBR). In situ field experiments demonstrated that BBD progressed along branches approximately twice as fast (1.7–2.4 times) during the austral summer month of January (0.99 ± 0.04 cm/day) than in the cooler months of July (0.58 ± 0.04 cm/day) and May (0.41 ± 0.07 cm/day). Transmission of BBD between colonies was also accelerated in warmer months, with signs of infection becoming visible 1.2 days earlier in January compared to May. The greater seawater temperatures by ∼2 to 3°C and light intensities by up to 650 μE/m2/s in January, suggest that rates of progression and transmission of BBD are linked to one or both of these parameters. Manipulative experiments in summer provide corroborative evidence that elevated temperatures increase rates of BBD progression, with the disease progressing 1.3 times more rapidly in the 32°C elevated temperature treatment than in the 30°C ambient treatment (1.17 ± 0.06 cm/day versus 0.92 ± 0.07 cm/day; F2,6 = 7.66, P = 0.022). In contrast, although a trend for greatest BBD progression was measured in elevated temperature treatments of 29°C (0.46 ± 0.07 cm/day) and 31°C (0.52 ± 0.06 cm/day) in winter, these rates did not differ significantly (F3,7 = 1.72, P = 0.249) from those measured for the ambient 27°C treatment (0.37 ± 0.06 cm/day) or the field controls (0.41 ± 0.09 cm/day). The lower rates of BBD progression in the 31°C winter treatment (0.52 ± 0.06 cm/day) than in the 30°C (0.92 ± 0.07 cm/day) summer treatment, may have been a response to 28-fold decreased light irradiance in the former, suggesting that high irradiance in combination with elevated temperatures may promote progression of BBD. Results from this study indicate that the impact of elevated temperature on BBD progression is complex with a combination of environmental factors including temperature and light playing key roles in progression and transmission of the disease.

THE ENERGY BALANCE DERIVED FROM COMPREHENSIVE OUTDOOR SCALE MODEL EXPERIMENT (COSMO)

Datasets of energy fluxes and surface temperature were obtained from Comprehensive Outdoor Scale Model Experiment (COSMO) in winter and spring-early summer. Daytime and daily total statistics of the ratio of heat storage (dQs) to net all-wave radiation (Q*) were investigated. We obtained following major findings. i) Daytime (Q* ≥ 0) dQs/Q* in winter were larger than those of spring-early summer. ii) Daytime dQs/Q* was slightly dependent on wind velocity and decreased with increasing wind velocity. iii) Daily total dQs/Q* was negative in winter and positive in summer, since daily total Q* was positive regardless of seasons while daily total dQs was negative in winter and positive in summer. The value of daily total dQs was strongly related to net daily increment of surface temperature.

Design criteria for in-buoy geoacoustic inversion using ship noise

Recent analysis of the ship noise data from R/V Oceanus, collected during the RAGS03 winter and base 2007 summer experiments, showed that robust geoacoustic inversions are possible under both winter and summer conditions. In littoral waters, fast‐traveling surface ships provide an excellent (broadband) source of opportunity to characterize the sea floor with a lightly populated vertical array. A well‐mixed and stable water‐column during the winter provides robust geoacoustic inversions up to 20 km in range. Under summer conditions, robust inversions are only possible up to 5 km in range, due to the near‐surface mixed‐layer and highly‐dynamic water‐column effects of internal waves. Matched‐field inversion results from both RAGS03 and Base07 experiments are presented using noise data from different ships at different ranges. Design criteria of a distributed system using single‐element receiver nodes for geoacoustic inversion and oceanographic monitoring are also discussed. [Work supported by ONR.]

Effect of melatonin on dopamine secretion in the hypothalamus of mature female common carp, Cyprinus carpio L

Background. The work was the continuation of previous study, which indicated that melatonin influences the inhibition of hypothalamic dopamine secretion in vitro. In the presently reported study, the influence of melatonin injection into the third cerebral ventricle on the release of dopamine was tested. The aim of this study was to investigate if and how melatonin affects dopamine secretion in the hypothalamus of mature female carp. Materials and methods. The concentration of dopamine in hypothalamic tissue was determined radioenzymatically. The experimental groups were fish deprived of melatonin by pinealectomy, fish that received intraventricular injections of melatonin, fish that received intraventricular injections of physiological saline, and intact fish (control treatment). The study was carried out in the summer during spawning and in the winter when fish gonads were regressed. Results. Melatonin injection resulted in an increase in dopamine concentration in the hypothalamus, which indicates that melatonin influenced aminergic nuclei inhibiting secretion of dopamine. Dopamine probably remained unreleased in the hypothalamic tissue, whereas in pinealectomized fish the lack of melatonin influenced continuous dopamine secretion, what was shown as the low dopamine level in the hypothalamus. The results confirmed the previous study effect of melatonin in mature female carp, and point to an inhibitory effect of intraventricularly injected melatonin on the release of dopamine from the hypothalamus. This effect occurred only in the summer experiment, indicating a seasonal impact of melatonin on the dopaminergic system. Conclusion. By inhibiting the release of hypothalamic dopamine, which blocks gonadotropin secretion, melatonin has a potential stimulatory effect on the release of LH and in this way may be involved in control of reproduction in carp.

Relative Salt Tolerance of Five Herbaceous Perennials

Use of recycled water to irrigate urban landscapes may be inevitable, because the freshwater supply has been diminishing and the population continues to grow in the arid and semiarid southwestern United States. However, little information exists on the performance of landscape plants irrigated with nonpotable water. Two greenhouse studies were conducted during the summer and the fall to characterize the relative salt tolerance of five herbaceous perennials by irrigating the plants with a saline solution at an electrical conductivity (EC) of 0.8 dS·m–1 (tap water), 2.0 dS·m–1, or 4.0 dS·m–1. In the summer study, after 10 weeks of treatment, Achillea millefolium L., Gaillardia aristata Foug., and Salvia coccinea Juss ex J. had an aesthetically acceptable appearance for landscape performance (visual quality scores of 4 points or more), whereas Agastache cana (Hook.) Woot. & Standl. and Echinacea purpurea (L.) Moench had relatively low tolerance to salinity. Dry weight of shoots of A. millefolium, A. cana, and G. arstata was lower at elevated salinity levels. In the fall study, A. millefolium, E. purpurea, G. arstata, and S. coccinea had acceptable growth and visual quality at elevated salinity levels, whereas A. cana had lower quality and reduced growth. Dry weight of shoots was lower in G. arstata and A. millefolium at an EC of 2.0 dS·m–1 or 4.0 dS·m–1. Leaf osmotic potential of all species in the summer experiment was significantly lower at higher salinity compared with the control. In the fall experiment, leaf osmotic potential in A. millefolium, E. purpurea, and G. aristata at 4 dS·m–1 was lower compared with lower salinity treatment and the control. Leaf osmotic potential in the fall was higher than that of the same species at the same salinity level in the summer experiment, indicating that plants in the fall were less stressed than in the summer. Combined the results from both experiments, the authors concluded that A. millefolium, G. arstata, and S. coccinea had a relatively high salt tolerance (as much as 4 dS·m–1 of irrigation water under greenhouse conditions) among the tested species, whereas A. cana and E. purpurea were not tolerant to salt and should not be irrigated with low-quality water.

Fate of cyromazine applied in nutrient solution to a gerbera ( Gerbera jamesonii) crop grown in a closed hydroponic system

Cyromazine was applied at two doses (375 and 750 mg l −1) via the nutrient solution in a winter crop of gerbera ( Gerbera jamesonii) grown on pumice in a closed-loop system. The persistence of cyromazine in the system and its uptake and distribution within the plant were studied for a period of 121 days by regularly collecting and analysing samples of nutrient solution, drainage solution, substrate, roots, leaves, and flowers. The residues of cyromazine in leaf were further studied in a summer experiment which lasted 50 days. The concentration of cyromazine fluctuated within a relatively high range in both the drainage solution and the nutrient solution supplied to the plants during the first day after its application but declined progressively thereafter. Nevertheless, 37 days after application, mean concentrations of 6.2 and 10.9 mg l −1 cyromazine were found in the drainage solution at low and high doses, respectively. The corresponding cyromazine concentrations 121 days after its application were 0.02 and 0.03 mg l −1. Similar values were measured also in the nutrient solution. The adsorption of cyromazine by the pumice was lower than 0.02 mg kg −1. The half-life time of cyromazine in the closed system was 9.65 days. In the winter experiment, the highest cyromazine concentrations were determined 17 days after application in root and 56 days in leaf and flower, regardless of the dose, while on day 121 the leaf concentrations were 52 and 62 mg kg −1 fresh weight (f. wt) at the low and the high dose, respectively. In the summer experiment, the leaf concentration of cyromazine reached a maximum (232 mg kg −1 f. wt) 14 days after its application and decreased only slightly on day 24, but dropped rapidly to 66 mg kg −1 f. wt on day 50. The above results indicate that cyromazine applied via the nutrient solution may persist for more than 120 days in closed hydroponic systems, while its maximum concentration in the plant tissues occurs several days after application.

Effects of artificial ultraviolet‐B radiation on growth and fatty acid composition of duckweed (Lemna minor)

Summary1. Duckweed (Lemna minor), collected either in summer or early fall was exposed under laboratory conditions to control (photosynthetically active and UV‐A radiation) or experimental (control plus UV‐B radiation) conditions.2. Growth and survival were determined by counting the number of green, and brown/white fronds following 1–5 or 11 days of irradiation. Growth of duckweed was impaired by exposure to UV‐B radiation in the fall experiment but not in the summer.3. Fatty acid compositions were analysed following 5 or 11 days of irradiation and a recovery period of 0, 5, 29 or 40 h. Concentrations of the major fatty acids, palmitic, linoleic (LA) and α‐linolenic (ALA) acids were similar in the summer and fall duckweed collections, but the summer samples had higher concentrations of the desaturation products of LA and ALA.4. UV‐B exposure had small, but significant, and contrasting effects on duckweed fatty acid concentrations. In the summer experiment, duckweed exposed to UV‐B had slightly lower concentrations of major fatty acids than control duckweed, while the reverse was true in the fall experiments.5. These minor effects of UV‐B on concentrations of LA and ALA would be unlikely to have a major impact on the supply of these essential fatty acids from duckweed to freshwater food webs.

The use of in situ and stream microcosm experiments to assess population‐ and community‐level responses to metals

We conducted field and stream microcosm experiments to assess population-level (density, size distribution) and community-level (species richness metrics, multivariate analysis of community composition) responses of macroinvertebrates to heavy metals in the Arkansas River, a mining-polluted stream in Colorado, USA. Experiments were conducted in spring and summer to coincide with early and late developmental stages (i.e., instars) of the mayfly Rhithrogena hageni. Results of field experiments showed significant mortality at metal-contaminated sites during summer when mayfly populations were dominated by small, early instars (mean dry wt = 0.13 mg). In contrast, no significant mortality was observed in spring when organisms were larger (mean dry wt = 1.78 mg). Multivariate analyses based on abundance of dominant taxa clearly separated reference and metal-impacted stations in summer experiments but showed little separation in spring. We observed no significant effects of metals on species richness, number of mayfly species, or EPT (species richness of Ephemeroptera, Plecoptera, and Trichoptera) in.either field experiment. Using stream microcosms, we established concentration-response relationships between heavy metals and R. hageni density, species richness, mayfly richness, and EPT. Density of R. hageni was generally more sensitive to metals than measures of species richness, and summer populations of R. hageni were more sensitive to metals than spring populations. Because the presence of large, relatively tolerant individuals in spring coincided with periods of higher metal concentrations, R. hageni was protected from toxic effects in this system. We conclude that phenology and developmental stage are important factors influencing responses of some aquatic macroinvertebrates to metals. Thus, timing bioassessments to coincide with the presence of these sensitive life stages can improve our ability to detect subtle contaminant effects.

Interactive influences of nutrient loading, zooplankton grazing, and microcystin synthetase gene expression on cyanobacterial bloom dynamics in a eutrophic New York lake

We investigated the dynamics and toxicity of cyanobacteria populations in Lake Agawam, a eutrophic New York lake, and concurrently conducted experiments to evaluate the contrasting effects of zooplankton (mesozooplankton and microzooplankton) grazing and nutrient loading on the abundance and toxin content of cyanobacteria populations. Molecular techniques were used to assess the presence and expression of the microcystin synthetase gene. Lake Agawam hosted dense blooms (>10 5 cells mL −1) of Microcystis sp. and Anabaena sp. with consistently elevated levels of microcystin (1.0–25 μg L −1) and lower levels of anatoxin-a (∼1.0 μg L −1 during late summer only). Polymerase chain reaction (PCR) analysis targeting the microcystin synthetase gene ( mcyE) indicated that Microcystis sp., and not Anabaena sp., was responsible for microcystin production in this system. Moreover, reverse transcriptase PCR (RT-PCR) indicated that the Microcystis population expressed the mcyE gene during summer months, but that gene expression declined to undetectable levels during the fall as in situ cell densities in the lake declined. During summer, when there was elevated Microcystis densities (>8 × 10 4 cells mL −1) expressing mcyE, experimental Daphnia sp. enrichment did not alter algal biomass (100% of experiments; n = 6). However, during fall months when the mcyE gene expression was not detected and Microcystis densities were lower and declining (4 × 10 3 to 5 × 10 4 cells mL −1), zooplankton enrichment yielded significantly reduced ( p < 0.05) cyanobacteria biomass relative to control treatments in most experiments (80%; n = 4). In contrast to mesozooplankton, microzooplankton actively grazed algal biomass at significant rates (1.2 ± 0.3 day −1) throughout the study. Microcystis and other cyanobacterial populations did not respond to nutrient amendments during early summer but experienced significantly increased growth rates and toxin concentrations (microcystin and anatoxin-a) during late summer and early fall nitrogen enrichment experiments. As such, the dominance of Microcystis sp. blooms during the summer was linked to nutrient replete conditions and the suppression of mesozooplankton (but not microzooplankton) grazing which itself appeared to be influenced by cellular toxin synthesis by Microcystis. The demise of the bloom was associated with N-limitation which reduced growth rates and toxin production by Microcystis and in turn may have permitted zooplankton to graze cells.

Is lack of mating competitiveness in spring linked to mating asynchrony between wild and mass‐reared codling moths from an operational sterile insect programme?

AbstractMating competitiveness and pheromone trap catches of mass‐reared, male codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), from the Osoyoos, British Columbia, Canada, mass‐rearing facility operated by the Okanagan‐Kootenay Sterile Insect Release Board, were compared to wild males using mark–release–recapture field experiments in spring, summer, and autumn at Summerland, British Columbia. In spring, significantly more wild diapause males mated with tethered, wild females than did non‐irradiated (0 Gy) or irradiated (100 or 250 Gy) non‐diapause, mass‐reared males. A lower dose of radiation did not improve mating competitiveness, nor catches of mass‐reared males released in spring. Median mating time for wild males was approximately 45 min earlier than mass‐reared males with most wild males (70.5%) mating before sunset and mass‐reared males mating at or shortly after sunset in spring. Superior mating competitiveness of wild males in spring was mirrored by greater recapture rates in pheromone‐baited traps. In summer, mating competitiveness of mass‐reared moths improved relative to wild males and there was a significant inverse relationship between radiation dose (0, 100, and 250 Gy) and competitiveness of mass‐reared males. In autumn, untreated, wild males were significantly more responsive to pheromone traps than non‐diapausing mass‐reared males receiving 250 Gy of radiation. Mass‐reared males, subjected to diapause‐inducing conditions as larvae and emerged from diapause before this irradiation treatment, were recaptured significantly more often than similarly irradiated, non‐diapause, mass‐reared males, but not more than untreated, diapause wild males. We hypothesize that differences between wild and mass‐reared males in daily timing or speed of responses to natural or synthetic pheromone sources under montane weather patterns typical of spring in British Columbia may partially explain poor activity of sterile males, and low sterile : wild overflooding ratios during spring when measured using pheromone traps by the sterile insect release programme in British Columbia.

Water‐Stress‐Induced Changes in Resin and Rubber Concentration and Distribution in Greenhouse‐Grown Guayule

Guayule (Parthenium argentatum A. Gray) is naturally subject to periods of water stress in its native habitat. It has been shown that, under cultivation, rubber yields increase with increasing irrigation, but rubber concentration per plant decreases. The effect of irrigation on resin concentration is unclear. The purpose of this study was to understand how resin concentration is affected by water stress, and why water stress increases rubber concentration. Greenhouse‐grown guayule plants were subjected to water stress in four experiments, each of 3 mo duration. Two experiments were conducted in the summer, the active growth period, and two experiments were conducted in the winter. The water‐stressed plants were irrigated when the average soil water potential reached either −0.6 MPa (first summer experiment) or −0.3 MPa (all subsequent experiments). Water‐stress effects were monitored by measuring growth, C exchange, biomass, and resin and rubber production. Water‐stressed plants had lower C exchange, growth, and leaf‐to‐stem ratio than well‐watered plants. Resin concentration did not respond consistently to water stress. Rubber concentration was generally higher in the water‐stressed plants than in the well‐watered plants as a result of decreased leaf biomass in both the summer (33 vs. 45 g kg−1) and winter (36 vs. 52 g kg−1) and decreased stem diameter in the summer (8.1 vs. 11.0 mm). Rubber is deposited mainly in the bark; therefore, reduced leaf biomass and stem diameter contribute to higher rubber concentration in the water‐stressed plants by increasing the relative amount of bark.

Effects of Faster Airflows on Human Thermal Comfort in Summer

A same comfort condition for the majority of people in temperate and tropical areas can be obtained with air-conditioning using a faster air velocity and a higher air temperature. This leads to more economical energy consumption. Thus, a location on a body was identified where comfort was attained efficiently by local airflow. The present study examined if any difference existed in subjects perception of the airflow between the back of the necks and ankles when local airflows of varying temperatures and velocities were directed at the two locations. The subjective responses in the summer experiments were discussed. The results indicate that the airflows caused stronger thermal sensation and airflow perception at the necks more so than at the ankles. The higher temperature airflow was evaluated to be more comfortable than the lower temperature airflow at both locations. The percentages dissatisfied (PDs) were smaller at the necks than the ankles.