Absolute thresholds and critical masking ratios were determined behaviorally for the European barn owl (Tyto alba guttata). It shows an excellent sensitivity throughout its hearing range with a minimum threshold of −14.2 dB sound pressure level
at 6.3 kHz, which is similar to the sensitivity found in the American barn owl (Tyto alba pratincola) and some other owls. Both the European and the American barn owl have a high upper-frequency limit of hearing exceeding
that in other bird species. Critical masking ratios, that can provide an estimate for the frequency selectivity in the barn
owl's hearing system, were determined with a noise of about 0 dB spectrum level. They increased from 19.1 dB at 2 kHz to 29.2 dB
at 8 kHz at a rate of 5.1 dB per octave. The corresponding critical ratio bandwidths were 81, 218, 562 and 831 Hz for test-tone
frequencies of 2, 4, 6.3 and 8 kHz, respectively. These values indicate, contrary to expectations based on the spatial representation
of frequencies on the basilar papilla, increasing bandwidths of auditory filters in the region of the barn owl's auditory
fovea. This increase, however, correlates with the increase in the bandwidths of tuning curves in the barn owl's auditory
fovea.
Accepted: 27 November 1997 相似文献
1. Critical thermal maxima (CTMax) and minima (CTMin) were determined for postlarvae and juveniles of Macrobrachium rosenbergii acclimated at 20, 23, 26, 29 and 32±1°C. 2. At each acclimation temperature the CTMax and CTMin for postlarvae were 37.3, 38.3, 39.0, 41.0, 41.6°C and 10.0, 11.0, 13.0, 14.8, 16.8°C respectively and for juveniles 36.5, 38.4, 39.2, 41.5, 42.0 and 10.5, 11.3, 13.3, 14.6, 16.4°C respectively. 3. We found no indication of significant differences (P>0.05) in the CTMax and CTMin of the prawn postlarvae and juveniles. 4. The zone of thermal tolerance base on the CTMax and CTMin boundaries for postlarvae was 821.2°C2 and 816.9°C2 for juveniles, showing a high degree of eurythermality. To cultivate this species it should be done in no less than 16°C (CTMin) and below 42°C. 相似文献
The influence of high temperature (33℃) on embryogenesis in isolated microspore culture of Chinese cabbage (Brassica campestris spp. pekinensis ) was investigated by microscpopy of FDA and DAPI. The microspores cultured at constant temperature of 25 ℃ lost their viability quickly and only few viable microspores were found after 7 days of culture. The morphology of the cultured microspores became as turgescent as the "rugby" which was similar to the mature pollen of the Chinese cabbage. The first nuclear division of the microspores was asymmetric. The microspores lost their capacity of embryogenesis under such condition. In contrast, when the microspores were cultured at 33℃ for 24 h before they were transfered to the culture condition of 25 ℃, their developmental pattern was changed. Some of the microspores could remain viable even for 7 days in culture, they became rounded off. The symmetric nuclear division pattern was induced. The frequency of such division was about 40%. Of the several new cell division types observed, the symmetric type was more frequent (55%) than others. The microspores treated under 33℃ were able to form embryoids via embryogenesis. The critical period of high temperature treatment on microspore culture of Chinese cabbage was about the initial 12 h, if the cell division index of microspore was concerned, but the period was the initial 24 h if the frequency of embryogenesis was considered. 相似文献
Three species of Antarctic mites, Alaskozetes antarcticus, Hydrogamasellus antarcticus and Rhagidia gerlachei, are abundant in the vicinity of Palmer Station, Antarctica. No single mechanism for reducing water stress was shared by
all three species. A. antarcticus and R. gerlachei (both ca. 200 μg) are over twice as large as H. antarcticus (ca. 90 μg), but all had similar body water content (67%) and tolerated a loss of up to 35% of their body water before succumbing
to dehydration. All imbibed free water and had the capacity to reduce water loss behaviorally by forming clusters. Alaskozetes antarcticus was distinct in that it relied heavily on water conservation (xerophilic classification) that was largely achieved by its
thick cuticular armor, a feature shared by all members of this suborder (Oribatida), and abundant cuticular hydrocarbons.
In comparison to the other two species, A. antarcticus was coated with 2–3× the amount of cuticular hydrocarbons, had a 20-fold reduction in net transpiration rate, and had a critical
transition temperature (CTT) that indicates a pronounced suppression in activation energy (Ea) at temperatures below 25°C. In contrast, H. antarcticus and R. gerlachei lack a CTT, have lower amounts of cuticular hydrocarbons and have low Eas and high net transpiration rates, classifying them as hydrophilic. Only H. antarcticus was capable of utilizing water vapor to replenish its water stores, but it could do so only at relative humidities close
to saturation (95–98 %RH). Thus, H. antarcticus and R. gerlachei require wet habitats and low temperature to counter water loss, and replace lost water behaviorally through predation. Compared
to mites from the temperate zone, all three Antarctic species had a lower water content, a feature that commonly enhances
cold tolerance. 相似文献
King penguins (Aptenodytes patagonicus) can fast for over a month. However, they return to sea to forage before their body mass reaches a critical value (cMb),
beyond which there is an increase in rate of mass loss and in protein catabolism, termed phase III of fasting. Thus when studying
king penguins onshore, accurate estimation of their cMb and, in turn, the date at which that body mass would be reached, will
be informative to behavioural and physiological data being collected. For penguins being studied during fasts in captivity,
knowing cMb is particularly important because of the need to release the birds back into their colony while they are still
in good nutritional condition. The present study investigates the validity of using measures of beak, flipper and foot length
together to estimate cMb in king penguins and provides a simple and effective prediction equation for researchers. The three
morphometric measurements, along with body mass just prior to going to sea after the moult fast (taken to represent cMb),
were obtained for nine king penguins in a colony at the Crozet Archipelago. A multiple linear regression of the three morphometric
measurements against cMb provided an R2 of 71.2%. Mean absolute percentage error of the estimate of cMb over the nine birds was 8.82 ± 1.20%. The described technique
could probably be employed for estimating cMb in other long-fasting seabirds. 相似文献
Previous studies have failed to identify an activational role for estradiol in the paternal behavior of Phodopus campbelli fathers. However, none of these studies addressed a developmental role that estradiol might play in establishing paternal behavior in this species. Males were orally administered the aromatase inhibitor letrozole (1 mg/kg/day) for three days at 18, 34, or 90 days of age. As adults, males were tested for paternal and sexual behavior. Letrozole treatment at 18 days resulted in males that spent less time huddling over pups during the birth, and had higher pup losses and male-biased pup survival for the first litter. Letrozole treatment at 34 days resulted in males that had altered sexual behavior; males had a longer interval between mounts and between intromissions, and took longer to achieve ejaculations over the first three ejaculatory series. Furthermore, these males sired smaller first litters and produced second litters with a male-biased sex ratio. Males treated with letrozole as adults showed a modest increase in paternal care during the birth, but pup development and survival were not altered. There was no effect of treatment on attack or retrieval behavior either as sexually naive adults or as new fathers. Thus, the results of the present study suggest that estradiol acts during adolescence to establish the normal expression of midwifery behavior and sexual behavior during adulthood. 相似文献
Denitrification efficiency [DE; (N2 − N/(DIN + N2 − N) × 100%)] as an indicator of change associated with nutrient over-enrichment was evaluated for 22 shallow coastal ecosystems
in Australia. The rate of carbon decomposition (which can be considered a proxy for carbon loading) is an important control
on the efficiency with which coastal sediments in depositional mud basins with low water column nitrate concentrations recycle
nitrogen as N2. The relationship between DE and carbon loading is due to changes in carbon and nitrate (NO3) supply associated with sediment biocomplexity. At the DE optimum (500–1,000 μmol m−2 h−1), there is an overlap of aerobic and anaerobic respiration zones (caused primarily by the existence of anaerobic micro-niches
within the oxic zone, and oxidized burrow structures penetrating into the anaerobic zone), which enhances denitrification
by improving both the organic carbon and nitrate supply to denitrifiers. On either side of the DE optimum zone, there is a
reduction in denitrification sites as the sediment loses its three-dimensional complexity. At low organic carbon loadings,
a thick oxic zone with low macrofauna biomass exists, resulting in limited anoxic sites for denitrification, and at high carbon
loadings, there is a thick anoxic zone and a resultant lack of oxygen for nitrification and associated NO3 production. We propose a trophic scheme for defining critical (sustainable) carbon loading rates and possible thresholds
for shallow coastal ecosystems based on the relationship between denitrification efficiency and carbon loading for 17 of the
22 Australian coastal ecosystems. The denitrification efficiency “optimum” occurs between carbon loadings of about 50 and
100 g C m−2 year−1. Coastal managers can use this simple trophic scheme to classify the current state of their shallow coastal ecosystems and
for determining what carbon loading rate is necessary to achieve any future state.
Guest editors: J. H. Andersen & D. J. Conley
Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of
Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark 相似文献
This paper compared two general methods for assessing critical fusion frequency in hens (gallus gallus domesticus). The first method was a conditional discrimination procedure with the stimuli presented successively. The second was a two-alternative forced-choice procedure with the stimuli presented simultaneously. It was found that both methods of stimulus presentation gave comparable results suggesting that either method is useful when investigating psychophysics in animals. The results also show that hens’ critical fusion frequency is considerably higher than that of humans which may account for hens’ inability to recognise images presented on standard computer or television monitors. 相似文献
Since the results of the women health initiative study showing an overall negative risk-benefit ratio with 0.625 mg of conjugated estrogens plus 2.5 mg of medroxyprogesterone acetate, the use of the lowest effective dose of steroids in hormone replacement therapy (HRT) is recommended.
A low-dose regimen appears to induce less side effects such as breast tenderness or leg pain than do higher dose preparations.
The decrease in hot flashes with low-dose estrogens, range 60–70%, is less than the 80–90% reduction with standard dosing. But this mean that 60–70% of menopausal women do not need higher doses.
The same applies to bone preservation which is dose dependent: the number of non-respondant women will be higher than with standard doses. However, randomized double-blind, placebo controls trials have defined positive effects on bone of low doses of HRT with adequate calcium and Vitamin D in elderly women. The use of bone densitometry and of biochemical markers of bone turnover is mandatory in women using low or ultra-low-dose preparations.
In spite of the lack of trials conducted with low-dose HRT, this treatment seems to be safer:
• the plasma levels of estradiol are lower; as far as breast cancer risk is concerned, the decrease of this subrogate marker is considered as favourable;
• the increase in breast density is less pronounced;
• the nurses's health study found a dose relationship for stroke, with no increase in risk with low-dose of estrogens;
• the effects on subrogate markers of cardiovascular risk seem to be more favourable.
Beside the low-dose HRT, one must consider some other facts:
• the “critical window” theory: it is biologically plausible that HRT, if started early after the menopause can slow the progression of coronary atherosclerosis;
• the way of administration of HRT: some observational studies have shown no increase in the risk of venous thromboembolism risk among women treated with transdermal estrogens;
• the progestogen used: a French cohort study recently performed found no increase in breast cancer risk with the use of micronized progesterone meanwhile the increase in risk observed with other progestogens was similar to the findings of the WHI study.
In the future, it is conceivable that more comprehensive pharmacogenomic studies will lead to effective algorithms for individualizing the right dose of steroids to be used in HRT. 相似文献