Diel changes in the benthos of stones and of drift in a southern Australian upland stream

Diel changes in the density of the fauna of stones and of drift were investigated in the Toorongo River, an upland river of southern Australia. The densities of the ten most common taxa and of the total fauna in the drift and on the stones were negatively correlated, with 16 out of 33 cases being significant (p < 0.05). Five of the ten most common taxa displayed a general trend of reaching day-time peaks in the benthos (11 out of 15 cases) and night-time peaks in the drift (10 out of 15 cases). The total density on the stones reached a significant peak in the day-time while the total drift density peaked at night.     

The effects of nerve growth factor and dibutyryl cyclic AMP on cytoskeletal densities in cultured sensory ganglia.

The effects of nerve growth factor (NGF) and dibutyryl cyclic AMP (DBC) on the density of cytoskeletal structures in cultured dorsal root ganglia were examined using morphometric techniques. After 24 hr in culture, NGF-treated neurites were longer than either DBC-treated or control neurites. At 48 hr, neurites produced in response to NGF and DBC were of equivalent length, while controls were considerably shorter. Comparison of electron micrographs of neuritic profiles revealed some differences of area and cytoskeletal density between treatment groups. Morphometric analysis was used to determine these differences under several growth conditions, at various rates of elongation and at different neurite lengths. As shown by analysis of variance, both NGF-treated and control neurites tapered in diameter at 48 hr in vitro, while DBC-induced neurites increased in area. An increase in cytoskeletal density for all treatment groups indicated that density was not always correlated with changes in area. An increased density of microtubules as compared to neurofilaments was seen at 24 hr, with equal densities of both cytoskeletal elements present after 48 hr in vitro. Comparisons between individual groups of data indicated that NGF-treated neurites relied primarily on microtubular density at 24 hr in vitro, when NGF induced longer, faster growing neurites. At 48 hr, there was an increase in neurofilaments proximal to the explant in the presence of DBC, implying that DBC may cause increased synthesis and/or transport of these structures. A comparison of microtubule to neurofilament ratios indicated that at 24 hr, there was always a greater density of microtubules. However, after 48 hr, neurofilament density increased such that there were equivalent densities of both cytoskeletal elements, possibly due to the overall increase in length observed in each treatment group. These data imply that 1) neurites with different rates of elongation may exhibit differences in cytoskeletal density; 2) neurites of equivalent lengths may be of differing stabilities; 3) NGF and DBC produce neurites with different cytoskeletal densities, implying divergent mechanisms of neurite induction; 4) the presence or absence of NGF may be partially responsible for variations in cytoskeletal densities observed between peripheral and central processes of DRG during development.     

Diel vertical migration by males,females, copepodids and nauplii in a limnetic population of diaptomus (Copepoda)

Diel vertical migration (DVM) by the sexes and life history stages of the copepod Diaptomus novamexicanus (Herrick) was investigated during two summers in a subalpine lake (Castle Lake, California, USA). Migratory behavior was quantified repeatedly by 1300 and 21–2200 hr sampling in the epilimnion. Population density and vertical distribution were estimated routinely at 1300 hr and at 2200 hr on selected dates. Males had greater night to day biomass differentials and ratios than females. The sexes showed comparable DVM participation (% of total biomass migrating) and amplitudes of migration (distance of ascent). Copepodids displayed higher participation, night/day ratios and amplitudes than younger copepods, but adult participation differed only from that of nauplii. Active participation in high amplitude ascents thus increased with age and was greatest in adult males. Analysis suggests that such relative behaviors probably occur in most limnetic Diaptomus, and that the magnitude of ascent into the epilimnion is associated with daytime vertical distribution.     

One week of exposure to 50 Hz, vertical magnetic field does not reduce urinary 6-sulphatoxymelatonin excretion of male wistar rats

The effect of exposure to 100 or 50 microT, 50 Hz, vertical magnetic field on the excretion of 6-sulphatoxymelatonin (6SM) in the nocturnal urine of rats was studied. Twelve male Wistar rats were kept under 12:12 hr light:dark conditions. The nocturnal urine of animals was collected in metabolic cages over 4 consecutive weeks. The concentration of 6SM in the rat urine was measured by 125I radioimmunoassay and normalized to creatinine concentration. After the first week of urine collection, 6 rats were exposed to 100 microT or 50 microT flux density magnetic fields (MF) for 8 hr daily for 1 week. It was found that the excretion of the primary metabolite of melatonin in the urine, 6SM, did not show statistically significant changes during and after magnetic field exposure.     

Individual and combined effects of fish predation and bed disturbance on stream benthic communities: a streamside channel experiment

1. The composition and spatiotemporal dynamics of biological communities are influenced by biotic processes, such as predation and competition, but also by physical disturbances, such as floods in running waters. However, the interplay of disturbance with predation is still poorly understood, especially in frequently disturbed streams. Further, different predator species can affect prey communities in different ways depending on their feeding mode and efficiency. 2. We investigated the individual and combined effects of flood‐induced bed disturbance and fish predation on the benthos for 4 weeks in 18 streamside channels fed by a flood‐prone New Zealand river. Bed movements caused by floods were simulated by tumbling the substratum in half the channels. Six channels each were stocked with introduced brown trout (Salmo trutta) or native upland bully (Gobiomorphus breviceps) or had fish excluded. We studied algal biomass and both invertebrate density and daytime activity on surface stones on several dates after the disturbance, invertebrate community composition in the substrata of the entire channels on day 28 and leaf decomposition rates over the 28‐day period. 3. Disturbance affected algal biomass and density, richness and activity of surface stone invertebrates, and overall density and richness of channel invertebrates. Presence or absence of fish, by contrast, did not influence overall invertebrate standing stocks when subsurface substrata were included but did affect invertebrate densities on surface stones in 45% of all analysed cases and invertebrate activity on surface stones in all cases. Leaf decomposition rates were not influenced at all by the experimental manipulations. 4. Native upland bullies featured more often than exotic brown trout in causing invertebrate density changes and equally often in causing changes to grazer behaviour. Overall, our results imply that fish predation can have strong effects on the benthic invertebrate community in frequently disturbed streams, especially via behavioural changes.     

Short-Term Regulation of Crassulacean Acid Metabolism Activity in a Tropical Hemiepiphyte,Clusia uvitana

Diel courses of net CO2 exchange of leaves were studied in Clusia uvitana (Clusiaceae), a tropical Crassulacean acid metabolism (CAM) hemiepiphyte, growing in the crown of a 47-m tall kapok tree on Barro Colorado Island, Panama. Measurements on days without precipitation showed that net uptake of atmospheric CO2 occurred at night, a feature of CAM, as well as in the early morning and late afternoon. During 36 h of almost continuous rainfall, nocturnal net CO2 uptake was abolished and the diel pattern of net CO2 exchange became similar to that of a C3 plant. Exposing well-watered, potted plants of Clusia in the laboratory to temperatures and photosynthetic photon flux densities similar to those during the tropical rainstorm also abolished nocturnal net CO2 uptake. In contrast, Kalanchoe pinnata (Crassulaceae), an obligate CAM plant, still showed net CO2 dark fixation following the same low-light and moderate-temperature conditions, albeit at decreased rates. During these 12-h photoperiods, titratable acidity in Clusia increased slightly above its high level measured at the end of the previous dark period, whereas in Kalanchoe, the acid content decreased by about 40%. A survey among outer canopy leaves of Clusia on Barro Colorado Island showed that leaves that exhibited little or no nocturnal acidification maintained high levels of H+ at dawn and dusk. Progressively lower levels of H+ at dusk were accompanied by progressively higher nocturnal increases in H+. The data suggest that in C. uvitana the rapid switching between CAM- and C3-type carbon fixation that may occur within 24 h in response to environmental changes is controlled by the acidity status of the leaves in the light. Nocturnal CO2 fixation is enhanced by conditions that decrease the organic acid content during the light period.     

Pituitary prolactin concentrations associated with daily prolactin surges in pseudopregnant rats

During pseudopregnancy (PSP) two surges of prolactin (PRL) secretion from the pituitary are observed, the nocturnal surge at dawn and the diurnal surge in the evening. An attempt was made to clarify the correlation between changes in serum and pituitary PRL concentrations on day 5-6 of PSP. During the nocturnal surge, pituitary PRL concentration decreased significantly from 0000 hr to 0300-0600 hr. On the other hand, the high pituitary PRL concentration remained unchanged during the diurnal surge from 1200 hr to 1800 hr. These findings suggest that the nocturnal and diurnal PRL surges are regulated by separate controlling mechanisms.     

Observations of daily activity patterns in two captive short-nosed echidnas,Tachyglossus aculeatus

Daily activity patterns of a pair of short-nosed echidnas, Tachyglossus aculeatus, at the Topeka Zoo were observed once monthly for 1 year. These echidnas remained primarily nocturnal throughout the year. In observations when both echidnas exhibited extended periods of activity (5 hours or more) there was a high correlation in times activity began between the two animals. Activity patterns varied throughout the year possibly associated with changes in temperature and/or photoperiod. Diel temperature changes and noise levels did not appear to be major factors influencing activity in this study.     

COLONIZATION AND STANDING CROPS OF EPILITHIC ALGAE IN THE SUSQUEHANNA RIVER,PENNSYLVANIA1

A SCUBA diver, using a bar-clamp sampler, collected quantitative epilithic algae samples from artificial substrates (slate and acrylic plates) and river stones at two stations on the Susquehanna River bottom in 1974. At Falls, Pennsylvania, algal colonization on monthly plates (submerged for ca. 30 day periods) was most rapid between September and October. In winter, when algal density on cumulative plates (submerged 2–13 mo) and on stones present in the river peaked at 18,100 and 21,900 units/ mm², respectively, colonization of clean monthly plates nearly ceased. Similar colonization patterns were observed in a portion of the river polluted by coal mine drainages (SSES), but expansion of the algae population at SSES was inhibited by iron in the effluents, and densities never exceeded 2,400 units/mm² on stones or plates. Diatoms composed 95% of the overall standing crop at Falls and 65% at SSES.     

The feeding relationships of two invertebrate predators in a New Zealand river

The size frequency distributions and foods of the larvae of Archichauliodes diversus (Megaloptera: Corydalidae) and Stenoperla prasina (Plecoptera: Eustheniidae) were studied for a year in the Glentui River, South Island, New Zealand. These two species are the largest invertebrate predators inhabiting streams and rivers in New Zealand, where they are the only carnivorous members of their respective orders. Both species occupied the same habitat with A. diversus being slightly more abundant in most months. Many small larvae occurred within the sediments of the stream bed, whereas more larger larvae were found on stones lying on the surface. A wide size range of larvae was present throughout the year and the median size (in terms of head width) of both species was similar in most months. Larval growth could not be determined from field data and the life cycles of both species can be described as non-seasonal. Quantitative sampling in 5 months provided estimates of population densities. These were maximal in December when values of 136/m² for A. diversus and 114/m² for S. prasina were obtained. Larval Chironomidae and mayflies of the genus Deleatidium were the most frequently taken prey of both predators in all months, and no strong relationship between size or species of predator and size of prey was found. Caseless trichopteran larvae formed a less important component of the diets of both species and detritus was ingested by some individuals. No instances of cannibalism and only one example of cross-predation by each predator was seen. Diel sampling in November showed that large Deleatidium larvae were relatively more abundant in the guts of insect predators and in nocturnal drift samples than in the benthos. This suggests that their greater activity at night may increase their susceptibility to predation by nocturnal feeders. No clear ecological segregation of the two species with respect to habitat or prey utilization was found and there was no obvious interspecific competition for food, which appeared to be abundant at all times. Finally, the prevalence of non-seasonal life cycles in New Zealand aquatic insects is discussed in relation to the low degree of speciation in several groups.     

Habitat structure,resources and diversity: the separate effects of surface roughness and macroalgae on stream invertebrates

Habitat structure has pervasive effects on community composition and diversity, with physically complex habitats often containing more species than physically simple ones. What factors or mechanism drive this pattern is little understood, but a complicating problem is that different sources of habitat structure can be confounded in both surveys and experiments. In this study, we carried out an experiment in which two sources of habitat structure, attached macroalgae and substrate surface texture, were separately manipulated to discern their joint and separate effects upon the diversity and composition of colonizing macroinvertebrates in a stony, upland stream. Because stream algae vary markedly in abundance in both space and time, we also sampled the epilithon of stream stones at two spatial scales on eight dates over 2 years to gain some preliminary data on how stream algae vary between individual substrata over time. Experimental substrata had either a smooth (siltstones, sandstones, crystal-poor felsic volcanics, plain paving bricks) or rough (granodiorites, crystal-rich felsic volcanics, sand-blasted paving bricks) surface. We allowed these substrata to be colonized naturally by macroalgae, mostly the filamentous red alga Audouinella hermannii. Half of each of the rough and smooth substrata were selected at random and the macroalgae gently sheared off. All substrata were defaunated with a household insecticide with little field persistence, set out randomly through the study riffle, and invertebrates allowed to colonize them for 14 days. Some substrata were sampled immediately to check the efficacy of faunal and algal removals, which proved to be successful. Experimental results showed that both surface texture and macroalgae increase species richness independently of each other. Surface texture had no effect on densities, while macroalgae increased colonization densities, but rarefaction showed that both sources of habitat structure increased species richness above values expected simply on the basis of the numbers of colonists. However, reference stones with high macroalgal cover had the same species richness as those with low cover, suggesting that the effects of macroalgae on species richness are transient relative to those associated with surface texture. Epilithon samples taken at different times suggest that the magnitude of spatial variation in plant growth alters with time. If plants generally recolonize rough surfaces more quickly than smooth, then the effects of habitat structure on macroinvertebrates ought to be strongest after major disturbances during growing seasons of plants. Received: 1 September 1999 / Accepted: 10 January 2000     

Effect of density on magnitude of directional selection on seed mass and emergence time in Plantago wrightiana Dcne. (Plantaginaceae)

Although population density is believed to be an important factor influencing evolutionary processes, surprisingly few studies have documented the existence or nature of density-dependent selection. We quantified the effects of density on directional selection on seed mass (the mass of a sown seed) and emergence time in the greenhouse and field for the annual plant Plantago wrightiana. In the greenhouse, we quantified selection on seed mass and emergence time at each of five planting densities (1 m^–2 to 10,000 m^–2) using the relationship between final plant mass and each trait at each density. We observed no significant selection on either seed mass or emergence time when plants were grown alone. At all higher densities, there was significant selection favoring early emergence and large seed mass, but there were no significant differences among the selection gradients determined at densities greater than individually grown plants. In the field, we detected no relationship between the magnitude of selection for early emergence and density. Our results suggest that selection on seed mass and time of emergence is density dependent, but the relationship between density and the magnitude of directional selection on these traits is not continuously increasing. Over broad ranges of density in the greenhouse and in the field, there was no detectable relationship between density and the magnitude of directional selection.     

巢湖微囊藻和浮游甲壳动物昼夜垂直迁移的初步研究

2002年10月进行了巢湖微囊藻和几种优势浮游甲壳动物的昼夜垂直变化的研究,结果表明:微囊藻具有明显的昼夜垂直变化现象。白天上层水中的微囊藻密度显著高于下层水中,夜晚逐渐下沉使得下层水中的密度相对高于上层水。微囊藻与叶绿素a、水温、溶解氧和pH等均呈显著的正相关(p<0.01)。几种优势浮游甲壳动物的昼夜垂直迁移存在较大的差异。短尾秀体溞和角突网纹溞白天在下层水(1.5m和2.5m)中的密度较高,夜晚则倾向于在上层水(0m和0.5m)中活动。相反,卵形盘肠溞白天在上层水中密度较高,象鼻溞则在11:00和15:00时各水层中的密度显著高于夜晚。汤匙华哲水蚤和广布中剑水蚤白天倾向于在下层水中活动,夜晚则逐渐迁移到上层水中。许水蚤在夜晚和凌晨3:00时各水层中的密度显著高于白天。中华窄腹剑水蚤昼夜垂直变化不明显。微囊藻与短尾秀体溞密度呈显著的负相关,而与象鼻溞和卵形盘肠溞呈显著的正相关(p<0.01)。     

Ontogenetic changes in retinal structure and visual acuity: a comparative study of coral-reef teleosts with differing post-settlement lifestyles

Changes in retinal structure during settlement were investigated in four species of tropical reef-associated teleost fishes with differing periods of planktonic duration and post-settlement lifestyles. They were: Apogon doederleini (Apogonidae), a nocturnal planktivore; Stethojulis strigiventer (Labridae), a diurnal microcarnivore; Upeneus tragula (Mullidae), a carnivore which uses chin barbels to disturb invertebrates from the sediment; and Pomacentrus moluccensis (Pomacentridae), a diurnal herbivorous planktivore. The densities of cones, rods, cells in the inner nuclear layer and cells in the ganglion cell layer were estimated in a size range of each species. Visual acuity was calculated using cone densities and lens diameter. The ontogenetic sequence of changes in cell density was similar in all species but interspecific variation in the timing and rates of change was found and could be related to lifestyle. For example, cone densities decreased and rod densities increased most rapidly in the nocturnal species, A. doederleini, during settlement. In contrast, high cone densities were maintained in the species adopting a diurnal lifestyle. Theoretical visual acuity was found to increase rapidly as lens size increased, but was similar for all species at similar lens sizes, indicating the importance of larger eye size as a means for improving resolution during early stages of eye growth. It was concluded that for the species undergoing abrupt lifestyle changes at settlement, structural re-organisation of the retina is important for the survival of the fish as they leave the pelagic environment and take up their reef-associated lifestyle.     

Diel emigration and colonization responses of blackfly larvae (Diptera: Simuliidae) to ultraviolet radiation

1. Total counts of blackfly larvae densities over 30- and 57-h periods in experimental channels during May of 1996 & 1997 indicate that ultraviolet radiation (UV; 290–400 nm) may be important in stimulating emigration.
2. Under experimentally controlled solar UV exposure, larval densities at dawn in UV-shielded channels were 161% and 168% higher than in the UV-exposed channels. Larval densities in UV-exposed channels then decreased by 68.2% and 81.1% between dawn and early afternoon of the two days; density decreases in UV-shielded channels were slight, and not statistically significant, during the same periods.
3. Larvae within UV-exposed channels occupied shaded microhabitats during hours of intense solar radiation, suggesting that simuliid larvae can detect and respond to UV radiation over very short periods of time.
4. A cyclical pattern of UV-induced emigration during hours of increasing solar flux (06.30–13.30) and net immigration in the hours of decreasing solar flux and at night emerged. Thus stream invertebrates may be very sensitive to environmental changes, resulting in either increased UV flux or decreased shading of streams. Diel cycles in invertebrate densities should be taken into account in research designs and sampling protocols in order to identify and interpret correctly results of both periodic surveys and experiments.     

Assessing peridomestic entomological factors as predictors for Lyme disease.

The roles of entomologic risk factors, including density of nymphal blacklegged ticks (Ixodes scapularis), prevalence of nymphal infection with the etiologic agent (Borrelia burgdorferi), and density of infected nymphs, in determining the risk of human Lyme disease were assessed at residences in the endemic community of South Kingstown, RI. Nymphs were sampled between May and July from the wooded edge around 51 and 47 residential properties in 2002 and 2003, respectively. Nymphs were collected from all residences sampled. Tick densities, infection rates, and densities of infected nymphs were all significantly higher around homes reporting Lyme disease histories in 2003, while only infection rates were significantly higher in 2002. However, densities of infected nymphs did not significantly predict the probability of Lyme disease at a residence (by logistic regression) in either year. There were no significant differences in entomologic risk factors between homes with state-confirmed Lyme disease histories and homes with self-reported cases (not reported to the state health department). Therefore, although entomologic risk factors tended to be higher at residences with cases of Lyme disease, entomological indices, in the absence of human behavior measures, were not useful predictors of Lyme disease at the scale of individual residences in a tick-endemic community.     

Seasonality of serum testosterone levels and sperm density in Tursiops truncatus

We trained a mature male bottlenose dolphin, Tursiops truncatus, to provide semen samples on command. After completion of the 10-week training period, semen was collected twice weekly and blood was sampled twice monthly for a period of 28 months. Total sperm per ejaculate ranged from near 0 to 54.6 x 10(9) (n = 1332). Sperm densities from each session ranged from no sperm to 1,587 x 10(6)/ml (n = 241). Testosterone levels ranged from 1.1 to 54.4 ng/ml (n = 79). Seasonal variations were observed in total sperm per ejaculate, sperm density per ml of ejaculate, and in serum testosterone levels. Peak sperm densities were detected during September and October of three consecutive breeding seasons. Serum testosterone levels peaked in June, decreased during July and August, and were lowest in September and October, the period of greatest sperm density. Peak sperm production and density were coincident with the peak period of breeding activity but at a time when serum testosterone levels were lowest.     

Composition and structure of the molluscan assemblage associated with a Cymodocea nodosa bed in south-eastern Spain: seasonal and diel variation

The molluscan taxocoenosis associated with a Cymodocea nodosa seagrass bed was studied throughout 1?year in Genoveses Bay, in the MPA “Parque Natural Cabo de Gata-Níjar” (south-eastern Spain). A total of 64,824 individuals were collected and 54 species identified. The molluscan fauna was mainly composed of gastropods (99.56% of individuals, 43 spp.). The families Rissoidae (72.98%, 11 spp.) and Trochidae (16.93%, 7 spp.) were the most abundant and diversified in terms of number of species. Rissoa monodonta (47.1% dominance), Rissoa membranacea (25.1%) and Gibbula leucophaea (11.6%) proved the top dominant species in both diurnal and nocturnal samples. Bivalves (0.41%, 10 species) and cephalopods (0.03%, 1 species) represented only a low percentage of the molluscan taxocoenosis. The molluscan assemblage was mainly composed of species with a wide geographical distribution in Europe, followed by strictly Mediterranean species. The abundance was significantly higher in the cold (December, March) than in the warm months (June, July). Species richness (S) was higher in nocturnal than in diurnal samples, reaching maximal values in diurnal samples of March and June. Shannon–Wiener diversity (H′) values were generally higher in nocturnal samples than in diurnal ones, displaying minimum values in December and June, respectively. Evenness was similar in diurnal and nocturnal samples, with maximum values in July in both groups. S and H′ were also significantly different between diurnal and nocturnal samples. Multivariate analyses based on both qualitative and quantitative data showed a significant seasonal and diel variation. Diel changes revealed to be more distinct than seasonal ones.     

Physiological Responses in Wild Broodstocks of the Caspian Kutum (Rutilus frisii kutum) Subjected to Transportation Stress

Caspian Kutum (Rutilus frisii kutum) broodstocks in the wild were subjected to 2 different densities (100 and 300 kg m^?3) for 2 hr of transport, and their physiological responses were examined. Fifteen fish were placed into the plastic container for each replicate and blood was taken at 0, 10, 30, 60, and 120 min after transportation in different densities. Mean levels of cortisol and glucose as primary and secondary responses to the stress were significantly different between densities. Significant differences in both densities were observed in cortisol for all times and glucose levels at 30 and 120 min after transportation, and the highest values were found in both densities at 120 min. Testosterone concentrations declined considerably in the first 10 min, and then they showed a gradual decrease with a significant difference between 2 densities at 10 and 30 min after transportation. Serum estradiol reached the lowest level at 120 min after transportation, and differences were significant between the 2 densities after 30 min. Based on the results, it was concluded that Kutum broodstocks are sensitive to transport, especially at high density. Therefore, welfare during transport should be considered.