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1.
Ulf Sperens 《Oecologia》1997,109(3):368-373
Variation in fruit production and pre-dispersal seed predation by Argyresthia conjugella was studied in␣four populations of Sorbus aucuparia in northern Sweden.␣The number of infructescences, fruits per infructescence, consumed seeds and developed unattacked seeds
per fruit were scored in marked trees from 1984 to 1990. The results showed that the number of fruits produced in each population
determined the number of seed predators occurring in the host population, as the yearly number of seed predators was significantly
and positively correlated with yearly number of fruits, in all but one population. The seed predators showed a delay in response
to variation in number of fruits produced. This lag in response resulted in a large proportion of fruits being attacked and
seeds consumed in a bad fruiting year that followed a good fruiting year, and vice versa. The proportion of fruits attacked
and seeds consumed was largest in the population showing the greatest between-year variation in fruit production and lowest
in the population showing the lowest between-year variation in fruit production. Furthermore, the individuals within the former
population were synchronised, while they were not in the latter population. These results contradict one of the possible explanations
of mast-seeding, where large synchronised between-year variation is supposed to reduce pre-dispersal seed predation. Instead,
differences in attraction of the seed predator to differences in fruit crop size could explain the observed difference in
seed predation between the two populations with opposite fruiting patterns. Within each population, irrespective of year,
the proportion of fruits attacked and seeds consumed was independent of a tree's fruiting display. Therefore, trees with high
fruit production, despite harbouring the largest number of seed predators, produced the largest number of developed seeds
in absolute numbers, compared to trees that produced few fruits.
Received: 25 February 1996 / Accepted: 30 November 1996 相似文献
2.
Large floral displays should theoretically provide advantages to plants through increased pollinator visitation and resulting
fruit and seed set. However empirical tests of the response of pollinators to floral display size have been limited by a lack
of direct experimentation, and the results of such studies have been equivocal. In addition, other selective agents such as
pre-dispersal seed predators might modulate effects of floral display on pollination. By artificially altering flower number,
we examined the direct effects of floral display in the monocarpic herb, Ipomopsis aggregata (Polemoniaceae), on visitation rates by broad-tailed and rufous hummingbird pollinators, as well destruction of fruits by
a pre-dispersal seed predator (Hylemya: Anthomyiidae). In addition, we quantified the ultimate effects of flower number on female reproductive success. Plants with
larger floral displays were most likely to be visited first in any given foraging bout (P < 0.01). As expected, plants with more flowers received more total flower visits. However, we found no gain in the proportion
of flowers visited for many- versus few-flowered plants, or the total number of approaches/hour. In fact, a significantly
greater percentage of flowers were visited on few-flowered plants. Plants did not compensate for our reduction in flowers
by increasing investment in the number or proportion of flowers that set fruit, the number of seeds/fruit, or seed weight.
Pre-dispersal seed predation was greater for many- than for few-flowered plants (P < 0.001), but this did not offset the potential fitness gains of producing large displays. Our data support the hypothesis
that large floral displays function primarily in long-distance attraction of pollinators, and enhance maternal success.
Received: 21 March 1996 / Accepted: 24 October 1996 相似文献
3.
We studied the effects of host plant hybridization on the survival and mortality of the leaf-mining moth Phyllonorycter salicifoliella on hybrid and parental willow plants in the field and in a common garden experiment. P. salicifoliella survival differed significantly among three willow taxa in the field in 1994 but not in the field in 1995 or in the common
garden. Parasitism by eulophid wasps differed significantly among taxa in 1994 and appeared to account for the variation in
their survival. In the field in 1995, host feeding predation varied significant among taxa. The theory of tritrophic interactions
predicts that plant genotype can affect natural enemy impact, and this study supports this prediction. Significant variation
in survival and eulophid parasitism was also found among genotypes within taxa in the field in both years and in the common
garden experiment. The common garden results show that genetic differences in plants affect the herbivore-parasitoid interaction.
Variation among years in the patterns of survival and causes of mortality among field plants suggest that genotype by environment
interactions may be important.
Received: 1 March 1996 / Accepted: 4 November 1996 相似文献
4.
Background matching might lower the risk of seeds being eaten by seed predators that search visually. In aviary experiments,
we analyzed the selection of diff erent-colored seeds by ground-feeding finches (Fringillacoelebs and F.montifringilla) against four naturally occurring forest soil substrates. The substrates were fresh burn (black), 6-year-old burn (brown),
mineral soil (pale yellow) and Pleuroziumschreberi feather moss (green). We used color-sorted seeds of Pinussylvestris, a species with a large natural variation in seed color, ranging from pale yellow to black. Although seeds were scattered
on the substrates at a density of only 91 seeds m−2, birds removed seeds effectively. Both bird species found more pale than dark seeds on the fresh burn substrate. F. montifringilla also recovered more pale than dark seeds on the old burn, and more dark than pale seeds on mineral soil. In moss, the birds
found very few seeds compared to the other substrates, and there was no color discrimination. P.sylvestris is frequently regenerating after fire, suggesting that dark seeds would be favored under selection from visually searching
predators. Fire-adapted conifers with serotinous cones, e.g., Pinuscontorta ssp. latifolia, which spread their seeds primarily on freshly burnt surfaces, produce uniformly black or dark brown seeds. However, regeneration
of the non-serotinous P.sylvestris is often extended for several years after a fire, during which substrate color and structure change. This may have helped
to maintain variation in seed color. When regeneration of a plant species occurs on a substrate of uniform color, we believe
that selection by visually searching seed predators will result in the evolution of cryptic seed color.
Received: 16 August 1996 / Accepted: 30 November 1996 相似文献
5.
6.
Jonas Dahl 《Oecologia》1998,117(1-2):217-226
I assessed the impact of both vertebrate and invertebrate predators on a lotic benthic community in a 1-month-long experiment,
using enclosures containing cobble/gravel bottoms, with large-mesh netting that allowed invertebrates to drift freely. Brown
trout (Salmo trutta) and leeches (Erpobdella octoculata) were used as predators and four treatments were tested: a predator-free control, leeches only, trout only, and leeches and
trout together. A density of 26.7 leeches/m2 (20 leeches/enclosure) and 1.3 trout/m2 (one trout per enclosure) was stocked into the enclosures. The total biomass of invertebrate prey was significantly lower
in the trout and trout plus leech treatments than in the leech and control treatments, which were due to strong negative effects
of trout on Gammarus. On the individual prey taxon level, both trout and leeches affected the abundance of Asellus
,
Baetis and Ephemerella, whereas the abundance of Gammarus was only affected by trout, and the abundance of Orthocladiinae and Limnephilidae was only affected by leeches. In the treatment
with trout and leeches together, the abundance of Ephemerella and Baetis was higher than when trout or leeches were alone, which was probably due to predator interactions. Leeches and trout had
no effects on prey immigration but did affect per capita emigration rates. Both trout and leeches indirectly increased periphyton
biomass in enclosures, probably due to their strong effects on grazers. Both trout and leeches were size-selective predators,
with trout selecting large prey, and leeches selecting small prey. Size-selective predation by trout and leeches affected
the size structure of five commonly consumed prey taxa. Trout produced prey populations of small sizes owing to consumption
of large prey as well as increased emigration out of enclosures by these large prey. Leech predation produced prey assemblages
of larger size owing to consumption and increased emigration of small prey. These results suggest that in lotic habits, predatory
invertebrates can be as strong interactors as vertebrate predators.
Received: 23 June 1997 / Accepted: 4 May 1998 相似文献
7.
Post-dispersal seed predation and the establishment of vertebrate dispersed plants in Mediterranean scrublands 总被引:4,自引:0,他引:4
Philip E. Hulme 《Oecologia》1997,111(1):91-98
The post-dispersal fate of seeds and fruit (diaspores) of three vertebrate-dispersed trees, Crataegus monogyna, Prunus mahaleb and Taxus baccata, was studied in the Andalusian highlands, south-eastern Spain. Exclosures were used to quantify separately the impact of
vertebrates and invertebrates on seed removal in relation to diaspore density and microhabitat. The three plant species showed
marked differences in the percentage of diaspores removed, ranging from only 5% for C. monogyna to 87% for T. baccata. Although chaffinches (Fringilla coelebs) fed on diaspores, rodents (Apodemus sylvaticus) were the main vertebrate removers of seed and fruit. Two species of ant (Cataglyphis velox and Aphaenogaster iberica) were the only invertebrates observed to remove diaspores. However, the impact of ants was strongly seasonal and they only
removed P. mahaleb fruit to any significant extent. While removal of seed by rodents was equivalent to predation, ants were responsible for
secondary dispersal. However, their role was limited to infrequent, small-scale redistribution of fruit in the vicinity of
parent trees. Rodents and ants differed in their use of different microhabitats. Rodents foraged mostly beneath trees and
low shrubs and avoided open areas while the reverse was true of ants. Thus, patterns of post-dispersal seed removal will be
contigent on the relative abundance and distribution of ants and rodents. Studies which neglect to quantify separately the
impacts of these two guilds of seed removers may fail to elucidate the mechanisms underlying patterns of post-dispersal seed
removal. The coincidence of both increased seed deposition by the main avian dispersers (Turdus spp.) and increased seed predation with increasing vegetation height suggested that selection pressures other than post-dispersal
seed predation shape the spatial pattern of seed dispersal. Rather than providing a means of escaping post-dispersal seed
predators, dispersal appears to direct seeds to microhabitats most suitable for seedling survival. Nevertheless, the reliance
of most vertebrate-dispersed trees on regeneration by seed and the absence of persistent soil seed banks imply that post-dispersal
seed predators may exert a strong influence on the demography of the plants whose seeds they consume. Even where microsites
are limited, the coincidence of the most suitable microhabitats for seedling establishment with those where seed predation
is highest provide a means by which selective seed predators can influence community composition.
Received: 19 August 1996 / Accepted: 25 January 1997 相似文献
8.
V. M. King B. K. Follett 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(5):541-551
c-fos induction was investigated as a potential component in the avian photic entrainment pathway and as a possible means of locating
the central pacemaker in birds. In both quail (Coturnix coturnix japonica) and starlings (Sturnus vulgaris) exposure to 1 h of light induced Fos-lir in the visual suprachiasmatic nucleus but not in the medial suprachiasmatic nucleus. However, the degree of c-fos induction in the visual suprachiasmatic nucleus was similar at different circadian times despite the fact that the light
pulses caused differential phase shifts in the locomotor rhythm. For golden hamsters the same experiment resulted in significantly
different levels of Fos-lir in the suprachiasmatic nucleus, as well as different phase shifts. Starlings and hamsters were also entrained to T-cycles that caused a large daily phase shift (T = 21.5 h in starlings, T = 22.67 hours in hamsters), or no daily phase shift (T = free running period). No difference in the induced levels of Fos-lir in the visual suprachiasmatic nucleus region was observed between the two groups of starlings, but in hamsters there were
significantly different levels of Fos-lir in the suprachiasmatic nucleus between the two groups.
Accepted: 15 November 1996 相似文献
9.
We investigated how infection by the mermithid nematode Gasteromermis sp. affected predation on its nymphal mayfly host, Baetisbicaudatus, by two invertebrate predators – the stonefly nymphs of Kogotusmodestus and the caddisfly larvae of Rhyacophilahyalinata. Predation trials and behavioral observations were conducted in stream-side, flow-through experimental chambers. When parasitized
and unparasitized prey were offered in equal numbers, K. modestus consumed significantly more parasitized than unparasitized nymphs. R. hyalinata consumed equal numbers of both prey types. Behavioral observations of foraging K.␣modestus on parasitized and unparasitized prey suggested that the increased consumption of parasitized nymphs was due to differences
in the behavior of infected mayflies in response to the predator. Specifically, parasitized nymphs drifted less often to escape
an approaching predator (non-contact encounters) compared to unparasitized nymphs, which increased the number of contact encounters
and attacks that occurred between K.␣modestus and parasitized prey. Because all hosts are castrated, these behavioral alterations affect only the fitness of the parasite,
which is killed along with its host by invertebrate predation. We present a number of hypotheses to explain why the parasite
causes increased predation on its host. These include the large size of the parasite affecting the sensory abilities of the
host, the larger energetic costs of escape behavior for parasitized individuals, and natural selection from fish predation
against drifting behavior by parasitized individuals.
Received: 27 May 1996 / Accepted: 30 September 1996 相似文献
10.
Many studies have experimentally addressed the effects of a particular predator species on prey behavior. In nature, however,
prey frequently face multiple species of predators that often vary in their predatory mode and in their level of predation
risk. Relatively few studies have considered prey responses under these complex conditions. In Kentucky, the stream-dwelling
water strider (Aquariusremigis) coexists with many potentially dangerous predators, two of which are the green sunfish (Lepomiscyanellus) and the fishing spider (Dolomedesvittatus). Green sunfish occupy stream pools and attack water striders from below. In contrast, fishing spiders hunt along stream
shorelines where they perch on overhanging vegetation or rocks and attack water striders near shore. We compared how A. remigis individuals respond to these two very different predators in pools with one or both predators. The presence of sunfish in
pools had strong effects on male water strider behavior, including increased use of three types of refuge from sunfish (riffles,
climbing out of the water, sitting on the water but at the edges of pools), decreased activity and a decreased number of aggressive
males on the water. Spiders also influenced water strider behavior; male water striders avoided spiders by shifting away from
the edges of pools. Comparisons of the effects of the two predator species showed that in general, antipredator responses
by male water striders were stronger in pools with fish alone than in those with spiders alone. In the presence of both predators,
male water strider behavior (microhabitat use and activity) was generally similar to behavior in the presence of fish alone.
In contrast, female water striders showed no significant response to the presence of sunfish, and little response to the presence
of spiders. This lack of response could be because females spent much of their time in refuges even in the absence of predators
(apparently hiding from harassment by males). Both spiders and fish caused decreases in water strider mating activity. The
presence of fish reduced both the number of matings per pool (mating frequency), and mean mating durations. Spiders induced
a decrease in mean mating duration, but not in mating frequency. The largest reductions in mating activity occurred in pools
with both predators present. Pools with either spiders or fish alone suffered 15–20% water strider mortality during our experiment
(versus no mortality in predator-free pools). Extant theory suggests that when prey face conflicting microhabitat responses
to two predators (as in this study), the predators should have facilitative effects on predation rates (i.e., prey that avoid
one predator are often killed by the other and vice versa). Mortality rates in pools with both predators present, however,
were not significantly different from that predicted by a null model of multiple predator effects. The lack of predator facilitation
can be explained by the compensatory reductions in water strider activity and mating activity in the presence of both predators.
Received: 26 August 1996 / Accepted: 12 June 1998 相似文献
11.
A.-W. Pan J. He Y. Kinouchi Hisao Yamaguchi Hiroshi Miyamoto 《European journal of applied physiology and occupational physiology》1997,75(5):388-395
The present study investigated the mechanism of diving bradycardia. A group of 14 healthy untrained male subjects were examined
during breath-holding either out of the water (30–33°C), in head-out immersion, or in whole-body submersion (27–29°C) in a
diving pool. Blood velocity, blood volume flow in the carotid artery, diastolic blood pressure and electrocardiogram were
measured and recorded during the experiments. The peak blood velocity increased by 13.6% (P < 0.01) and R-wave amplitude increased by 57.1% (P < 0.005) when the subjects entered water from air. End-diastolic blood velocity in the carotid artery increased significantly during breath-holding, e.g. increased from 0.20 (SD 0.02) m · s−1 at rest to 0.33 (SD 0.04) m · s−1 (P < 0.001) at 50.0 s in breath-hold submersion to a 2.0-m depth. Blood volume flow in the carotid artery increased by 26.6%
(P < 0.05) at 30 s and 36.6% (P < 0.001) at 40 s in breath-hold submersion to a 2.0-m depth. Diastolic blood pressure increased by 15.4% (P < 0.01) at 60 s during breath-holding in head-out immersion. Blood volume flow, and diastolic blood pressure increased significantly more and faster during breath-holding in submersion than out of the
water. There was a good negative correlation with the heart rate: the root mean square correlation coefficient r was 0.73 (P < 0.001). It was concluded that an increased accumulation of blood in the aorta and arteries at end-diastole and decreased
venous return, caused by an increase in systemic peripheral resistance during breath-holding, underlies diving bradycardia.
Accepted: 22 November 1996 相似文献
12.
Malcolm S. Hill 《Oecologia》1998,117(1-2):143-150
Competition for space is an important process on tropical coral reefs. Few studies have examined the role sponges play in
community structure despite the fact that many sponges are competitively superior to reef-building corals in space acquisition.
Surveys conducted throughout the Florida Keys indicated that Chondrilla nucula was involved in about 30% of all coral-sponge interactions; this sponge has also been observed in 40–50% of coral-sponge
interactions on other Caribbean reefs. C. nucula is also the top prey item of the Hawksbill turtle, and among the preferred prey of several spongivorous fish. I examined
how predation influenced sponge competitive abilities (particularly those of C. nucula), and whether this type of indirect effect had important consequences for community dynamics in the Florida Keys. Exclusion
of sponge predators (primarily angelfish) resulted in increased sponge overgrowth, with a subsequent greater loss of coral
cover, compared to uncaged pairwise interactions. When caged, the corals Dichocoenia stokesii and Siderastrea sideraea lost significantly greater surface area and number of polyps to the sponge C. nucula compared to uncaged interactions. For caged interactions involving the sponge Ectyoplasia ferox, there was a trend for greater loss of S. sideraea surface area and polyps compared to uncaged interactions. Predation had a greater affect on C. nucula than on any of the other sponges examined. Predator exclusion experiments performed with naturally occurring coral-sponge
interactions demonstrated a significant decrease in total coral cover compared to uncaged controls. It is proposed that indirect
effects arising from spongivory (especially consumption of C. nucula) may have large community consequences. Species diversity on Caribbean reefs may be maintained, at least in part, by spongivores.
Received: 28 January 1998 / Accepted: 22 June 1998 相似文献
13.
Stem respiration of ponderosa pines grown in contrasting climates: implications for global climate change 总被引:7,自引:0,他引:7
We examined the effects of climate and allocation patterns on stem respiration in ponderosa pine (Pinus ponderosa) growing on identical substrate in the cool, moist Sierra Nevada mountains and the warm, dry, Great Basin Desert. These environments
are representative of current climatic conditions and those predicted to accompany a doubling of atmospheric CO2, respectively, throughout the range of many western north American conifers. A previous study found that trees growing in
the desert allocate proportionally more biomass to sapwood and less to leaf area than montane trees. We tested the hypothesis
that respiration rates of sapwood are lower in desert trees than in montane trees due to reduced stem maintenance respiration
(physiological acclimation) or reduced construction cost of stem tissue (structural acclimation). Maintenance respiration
per unit sapwood volume at 15°C did not differ between populations (desert: 6.39 ± 1.14 SE μmol m−3 s−1, montane: 6.54 ± 1.13 SE μmol m−3 s−1, P = 0.71) and declined with increasing stem diameter (P = 0.001). The temperature coefficient of respiration (Q
10) varied seasonally within both environments (P = 0.05). Construction cost of stem sapwood was the same in both environments (desert: 1.46 ± 0.009 SE g glucose g−1 sapwood, montane: 1.48 ± 0.009 SE glucose g−1 sapwood, P = 0.14). Annual construction respiration calculated from construction cost, percent carbon and relative growth rate was greater
in montane populations due to higher growth rates. These data provide no evidence of respiratory acclimation by desert trees.
Estimated yearly stem maintenance respiration was greater in large desert trees than in large montane trees because of higher
temperatures in the desert and because of increased allocation of biomass to sapwood. By analogy, these data suggest that
under predicted increases in temperature and aridity, potential increases in aboveground carbon gain due to enhanced photosynthetic
rates may be partially offset by increases in maintenance respiration in large trees growing in CO2-enriched atmospheres.
Received: 4 November 1996 / Accepted: 23 January 1997 相似文献
14.
S. Ohshima M. Murata W. Sakamoto Y. Ogura F. Motoyoshi 《Molecular & general genetics : MGG》1997,254(2):186-194
The Arabidopsis gene Terminal Flower 1 (TFL1) controls inflorescence meristem identity. A terminal flower (tfl1) mutant, which develops a terminal flower at the apex of the inflorescence, was induced by transformation with T-DNA. Using
a plant DNA fragment flanking the integrated T-DNA as a probe, a clone was selected from a wild-type genomic library. Comparative
sequence analysis of this clone with an EST clone (129D7T7) suggested the existence of a gene encoding a protein similar to
that encoded by the cen gene which controls inflorescence meristem identity in Antirrhinum. Nucleotide sequences of the region homologous to this putative TFL1 gene were compared between five chemically induced tfl1 mutants and their parental wild-type ecotypes. Every mutant was found to have a nucleotide substitution which could be responsible
for the tfl1 phenotype. This result confirmed that the cloned gene is TFL1 itself. In our tfl1 mutant, no nucleotide substitution was found in the transcribed region of the gene, and the T-DNA-insertion site was located
at 458 bp downstream of the putative polyadenylation signal, suggesting that an element important for expression of the TFL1 gene exists in this area.
Received: 14 November 1996 / Accepted: 29 November 1996 相似文献
15.
S. R. Soffe 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(6):711-715
Young Xenopus tadpoles were used to test whether the pattern of discharge in specific sensory neurons can determine the motor response
of a whole animal. Young Xenopus tadpoles show two main rhythmic behaviours: swimming and struggling. Touch-sensitive skin sensory neurons in the spinal cord
of immobilised tadpoles were penetrated singly or in pairs using microelectrodes to allow precise control of their firing
patterns. A single impulse in one Rohon-Beard neuron (= light touch) could sometimes trigger “fictive” swimming. Two to six
impulses at 30–50 Hz (= a light stroke) reliably triggered fictive swimming. Neither stimulus evoked fictive struggling. Twenty-five
or more impulses at 30–50 Hz (= pressure) could evoke a pattern of rhythmic bursts, distinct from swimming and suitable to
drive slower, stronger movements. This pattern showed some or all the characteristics of “fictive” struggling. These results
demonstrate clearly that sensory neurons can determine the pattern of motor output simply by their pattern of discharge. This
provides a simple form of behavioural selection according to stimulus.
Accepted: 28 November 1996 相似文献
16.
The unstable linear chromosome of Streptomyces lividans was circularized by homologous recombination and its terminal inverted repeats deleted. Strains with circularized chromosomes
showed no obvious phenotypic disadvantages compared to the wild type. However, they segregated about 20 times more chloramphenicol-sensitive
mutants than the wild type (24.3% vs. 1.4%), due to a higher incidence of large deletions. In addition, in all circularized
chromosomes amplification of 30–60 kb fragments was observed at the new chromosomal junction, to levels of approximately 10
copies per chromosome. Arginine auxotrophs that arose spontaneously among the progeny of strains with a circularized chromosome
showed high-copy-number amplification of the DNA element AUD1, as also seen in mutants of the wild type. These observations
demonstrate that the circular form of the Streptomyces chromosome is more unstable than the linear one.
Received: 28 July 1996 / Accepted: 18 November 1996 相似文献
17.
Isabelle Sendowski Gustave Savourey Yves Besnard Jacques Bittel 《European journal of applied physiology and occupational physiology》1997,75(6):471-477
To study the physiological responses induced by immersing in cold water various areas of the upper limb, 20 subjects immersed
either the index finger (T1), hand (T2) or forearm and hand (T3) for 30 min in 5°C water followed by a 15-min recovery period.
Skin temperature of the index finger, skin blood flow (Qsk) measured by laser Doppler flowmetry, as well as heart rate (HR) and mean arterial blood pressure (ˉBPa) were all monitored during the test. Cutaneous vascular conductance (CVC) was calculated as Qsk / ˉBPa. Cold induced vasodilatation (CIVD) indices were calculated from index finger skin temperature and CVC time courses. The
results showed that no differences in temperature, CVC or cardiovascular changes were observed between T2 and T3. During T1,
CIVD appeared earlier compared to T2 and T3 [5.90 (SEM 0.32) min in T1 vs 7.95 (SEM 0.86) min in T2 and 9.26 (SEM 0.78) min
in T3, P < 0.01]. The HR was unchanged in T1 whereas it increased significantly at the beginning of T2 and T3 [+13 (SEM 2) beats · min−1 in T2 and +15 (SEM 3) beats · min−1 in T3, P < 0.01] and then decreased at the end of the immersion [−12 (SEM 3) beats · min−1 in T2, and −15 (SEM 3) beats · min−1 in T3, P < 0.01]. Moreover, ˉBPaincreased at the beginning of T1 but was lower than in T2 and T3 [+9.3 (SEM 2.5) mmHg in T1, P < 0.05; +20.6 (SEM 2.6) mmHg and 26.5 (SEM 2.8) mmHg in T2 and T3, respectively, P < 0.01]. The rewarming during recovery was faster and higher in T1 compared to T2 and T3. These results showed that general
and local physiological responses observed during an upper limb cold water test differed according to the area immersed. Index
finger cooling led to earlier and faster CIVD without significant cardiovascular changes, whereas hand or forearm immersion
led to a delayed and slower CIVD with a bradycardia at the end of the test.
Accepted: 26 November 1996 相似文献
18.
K.-H. Esser B. Lud 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(5):513-522
In the lesser spear-nosed bat, Phyllostomus discolor, maternal directive calls are characterized by an individual type of sinusoidal frequency modulation (= SFM) pattern. Beside
modulation frequency, modulation depth, carrier frequency, and number of modulation cycles per call contribute to the mother's
vocal signature. Since juvenile P. discolor learn to adapt their isolation calls to the corresponding call characteristics of the own mother or even to playback of a
computer-stored directive call, if hand-reared in the absence of conspecifics, the bats' auditory system ought to be able
to resolve interindividual differences in communication call structure. However, quantitative psychoacoustic data on the discrimination
of SFM signals in this species are not available. Thus, in the present study, lesser spear-nosed bats were trained in a two-alternative
forced-choice procedure to discriminate between two alternatingly presented SFM sound signals differing in modulation frequency.
Other characteristics of acoustic stimuli were identical and designed to mimick the fundamental of species-specific calls.
By gradually reducing the difference in modulation frequency between both stimuli within the behavioural relevant range until
the animals' performance dropped below the 75%-correct level, a considerable auditory spectro-temporal resolution has been
revealed. Particularly in comparison to the overall interindividual variation of this call parameter (minimal modulation frequency = 49 Hz,
maximum = 100 Hz), the determined average difference limen for modulation frequency of 2.42 ± 0.29 Hz seems substantial and
sufficient for labelling individuals.
Accepted: 30 November 1996 相似文献
19.
Hilde Spielvogel Armando Rodriguez Brigitte Sempore Esperanza Caceres J.-M. Cottet-Emard Laurent Guillon R. Favier 《European journal of applied physiology and occupational physiology》1997,75(5):400-406
The present study was undertaken to determine the haematological and cardiovascular status, at rest and during prolonged
(1 h) submaximal exercise (approximately 70% of peak oxygen uptake) in a group (n = 12) of chronic coca users after chewing approximately 50 g of coca leaves. The results were compared to those obtained
in a group (n = 12) of nonchewers. At rest, coca chewing was accompanied by a significant increase in heart rate [from 60 (SEM 4) TO 76 (SEM 3)
beats · min−1], in haematocrit [from 53.2 (SEM 1.2) to 55.6 (SEM 1.1)%] in haemoglobin concentration, and plasma noradrenaline concentration
[from 2.8 (SEM 0.4) to 5.0 (SEM 0.5) μmol · l−1]. It was calculated that coca chewing for 1 h resulted in a significant decrease in blood [−4.3 (SEM 2.2)%] and plasma [−8.7 (SEM 1.2)%]
volume. During submaximal exercise, coca chewers displayed a significantly higher heart rate and mean arterial blood pressure.
The exercise-induced haemoconcentration was blunted in coca chewers compared to nonchewers. It was concluded that the coca-induced
fluid shift observed at rest in these coca chewers was not cumulative with that of exercise, and that the hypovolaemia induced
by coca chewing at rest compromised circulatory adjustments during exercise.
Accepted: 29 October 1996 相似文献
20.
Photoperiodic time measurement regulating larval diapause in the pitcher-plant mosquito, Wyeomyia smithii, varies in a close relationship with latitude. The critical photoperiod mediating the maintenance and termination of diapause
is positively correlated with latitude (r
2 = 0.977) among six populations from southern (30–31° N), intermediate (40° N), and northern (46–49° N) latitudes in North
America. The developmental response to unnaturally short and to unnaturally long photoperiods declines with increasing latitude,
so that longer critical photoperiods are associated with a downward rather than a lateral shift in the photoperiodic response
curve. Exotic light and dark cycles of varying period (T) with a short (10 h) photophase and a scotophase ranging from 14
(T = 24) to 62 (T = 72) h, reveal two geographic patterns: a decline in perturbability of the photoperiodic clock with increasing
latitude, and no change with latitude in the 21-h period of rising and falling development with increasing T. These results
show (1) that there is a rhythmic component to photoperiodic time measurement in W. smithii, (2) that the period of this rhythm is about 21 h in all populations, and (3) that more northern populations show decreasing
responsiveness to photoperiod and increasing stability against perturbation by exotic period lengths (T > 24). Previous studies
on W.␣smithii indicate that this single temperate species of a tropical and subtropical genus has evolved from south to north. We therefore
conclude that the evolution of increasing critical photoperiod in W. smithii during its adaptive radiation into North America has more likely involved the amplitude and not the period of the underlying
circadian pacemaker.
Received: 22 July 1996 / Accepted: 30 September 1996 相似文献