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1.
The Scallop theorem states that reciprocal methods of locomotion, such as jet propulsion or paddling, will not work in Stokes flow (Reynolds number=0). In nature the effective limit of jet propulsion is still in the range where inertial forces are significant. It appears that almost all animals that use jet propulsion swim at Reynolds numbers (Re) of about 5 or more. Juvenile squid and octopods hatch from the egg already swimming in this inertial regime. Juvenile jellyfish, or ephyrae, break off from polyps swimming at Re greater than 5. Many other organisms, such as scallops, rarely swim at Re less than 100. The limitations of jet propulsion at intermediate Re is explored here using the immersed boundary method to solve the 2D Navier-Stokes equations coupled to the motion of a simplified jellyfish. The contraction and expansion kinematics are prescribed, but the forward and backward swimming motions of the idealized jellyfish are emergent properties determined by the resulting fluid dynamics. Simulations are performed for both an oblate bell shape using a paddling mode of swimming and a prolate bell shape using jet propulsion. Average forward velocities and work put into the system are calculated for Re between 1 and 320. The results show that forward velocities rapidly decay with decreasing Re for all bell shapes when Re<10. Similarly, the work required to generate the pulsing motion increases significantly for Re<10. When compared to actual organisms, the swimming velocities and vortex separation patterns for the model prolate agree with those observed in Nemopsis bachei. The forward swimming velocities of the model oblate jellyfish after two pulse cycles are comparable to those reported for Aurelia aurita, but discrepancies are observed in the vortex dynamics between when the 2D model oblate jellyfish and the organism. This discrepancy is likely due to a combination of the differences between the 3D reality of the jellyfish and the 2D simplification, as well as the rigidity of the time varying geometry imposed by the idealized model.  相似文献   

2.
This study describes the first record of the whale shark Rhincodon typus association with the cannonball jellyfish Stomolophus meleagris in the Gulf of California, Mexico. Whale sharks were observed swimming and feeding among swarms of jellyfish, suggesting competition and predatory behaviour given the overlap in food preferences between both species. This finding is relevant because of the species‐wide distribution and the importance of these interactions, which should be considered in conservation strategies of R. typus and management of cannonball jellyfish fisheries.  相似文献   

3.
 Characteristics of the pelagic stages of reef fishes have generally been investigated at the family level, which may mask important differences among species. Here the variation in sustained swimming ability of the late pelagic stages is examined among species, within two families (Pomacentridae and Chaetodontidae). The pomacentrids displayed a 7.5-fold difference in sustained swimming ability across 24 species, while the chaetodontids displayed a 2-fold difference across 10 species. The variation within the Pomacentridae was not related to pelagic larval duration, post-settlement habitat or taxonomy. There was, however, a significant correlation between sustained swimming ability and total length (TL) of individuals (r=0.435, P<0.0001). Differences in the mean distance swum by pomacentrid species, however, was most strongly related to differences in mean wet weight (r=0.814, P<0.0001). When the mean distance swum by species was scaled with respect to mean TL there was still a strong correlation with mean wet weight (r=0.644, P<0.005). Among chaetodontid individuals TL and sustained swimming ability were not correlated (r=−0.004, P=0.978). Furthermore, sustained swimming ability was not significantly related to the trans-oceanic distribution of species in either family. The variation in sustained swimming ability, however, may contribute to explanations of the observed levels of gene flow within populations. Accepted: 24 November 1997  相似文献   

4.
Thirteen natural populations from throughout the range of the Chinese pine (Pinus tabulaeformis Carr.) were examined using inter-simple sequence repeat markers to characterize the genetic structure at the species level and to compare the extent and distribution of genetic variation among central, intermediate, and marginal populations. Although the total genetic variation in the Chinese pine was mainly maintained within populations, the genetic differentiation among populations was significant (P < 0.001). The genetic divergence was significantly correlated with geographic distance (P < 0.05). Genetic diversity tended to decrease from the central to intermediate and marginal populations. The marginal populations had significantly lower intrapopulation genetic diversity than central populations (P < 0.05). Cluster analysis based on Nei’s unbiased genetic distances confirmed the difference among four central populations and the rest. Both historical and contemporary factors may have played key roles in shaping the spatial genetic structure of this species.  相似文献   

5.
Dam construction is a major driver of ecological change in freshwater ecosystems. Fish populations have been shown to diverge in response to different flow velocity habitats, yet adaptations of fish populations to river and reservoir habitats created by dams remains poorly understood. We aimed to evaluate divergence of morphological traits and prolonged swimming speed performance between lotic and lentic populations of Australian smelt Retropinna semoni and quantify the relationship between prolonged swimming speed performance and morphology. Prolonged swimming speed performance was assessed for 15 individuals from each of three river and two reservoir populations of R. semoni using the critical swimming speed test (Ucrit). Body shape was characterized using geometric morphometrics, which was combined with fin aspect ratios and standard length to assess morphological divergence among the five populations. Best subsets model-selection was used to identify the morphological traits that best explain Ucrit variation among individuals. Our results indicate R. semoni from river populations had significantly higher prolonged swimming speed performance (Ucrit = 46.61 ± 0.98 cm s−1) than reservoir conspecifics (Ucrit = 35.57 ± 0.83 cm s−1; F1,74 = 58.624, Z = 35.938, P < 0.001). Similarly, R. semoni sampled from river populations had significantly higher fin aspect ratios (ARcaudal = 1.71 ± 0.04 and 1.29 ± 0.02 respectively; F(1,74) = 56.247, Z = 40.107, P < 0.001; ARpectoral = 1.85 ± 0.03 and 1.33 ± 0.02 respectively; F(1,74) = 7.156, Z = 4.055, P < 0.01). Best-subset analyses revealed Ucrit was most strongly correlated with pectoral and caudal fin aspect ratios (R2adj = 0.973, AICc = 41.54). Body shape, however, was subject to a three-way interaction among population, habitat and sex effects (F3,74 = 1.038. Z = 1.982; P < 0.05). Thus sexual dimorphism formed a significant component of unique and complex variation in body shape among populations from different habitat types. This study revealed profound effects of human-altered flow environments on locomotor morphology and its functional link to changes in swimming performance of a common freshwater fish. While past studies have indicated body shape may be an important axis for divergence between lotic and lentic populations of several freshwater fishes, fin aspect ratios were the most important predictor of swimming speed in our study. Differences in body morphology here were inconsistent between river and reservoir populations, suggesting this aspect of phenotype may be more strongly influenced by other factors such as predation and sexual dimorphism.  相似文献   

6.
Loggerhead turtle Caretta caretta L. hatchlings emerging from nests on the eastern coast of Florida swim offshore toward the Florida Current. Part of the trip is accomplished during an initial 20-h period of swimming (the “frenzy”); the remainder may take a day or more of oriented swimming. Swimming speeds are slower than those of green turtles Chelonia mydas L. Hatchlings are well oriented in an offshore direction when released into the ocean during the day or night. Completion of a crawl down the beach or a plunge into the surf are unnecessary for proper orientation. Immediately after entering the ocean at night, responses to light appear essential for oriented swimming. However, present hypotheses based upon phototropotaxis may not account for orientation later in the migration.  相似文献   

7.
The response of individual Cryptomonas cells to continuous lightwas recorded using infrared video-micrography. Swimming directionsand temporal shifts in swimming direction of each cell weremeasured. White light of 0.1–1 W m–2 elicited apositive phototactic orientation, but did not induce any photophobicresponse. Light of 100 W m–2 induced a photophobic responseat the onset of actinic irradiation, but did not induce positivephototactic orientation. No correlation between positive phototacticorientation and photophobic response was found in this species.The direction toward the light source was defined as 0°,and the direction away from the source as 180°. Within 2s after the onset of lateral monochromatic light of 570 nm at0.1 W m–2, cells which were swimming in a direction ofless than 120° predominantly shifted their course towardthe light source. Cells swimming in directions of larger than120° shifted their course as randomly as those in the dark.Thus, for phototactic orientation, the cells must perceive thelight from their anterior side. (Received July 29, 1985; Accepted November 4, 1985)  相似文献   

8.
Climatic shifts within recent decades created favorable conditions for invasive species flourishing in more Northern parts of Europe. Our study was aimed at evaluation of genetic variability and habitat features of Impatiens parviflora populations growing in Lithuania. Twenty one populations were selected and analysed using simple sequence repeat (SSR) and randomly amplified polymorphic DNA (RAPD) assays. Evaluated by SSRs, 315 individuals were all monomorphic and homozygous at 4 loci and heterozygous at 1 locus. RAPD analyses revealed that the percentage of polymorphic DNA loci (% P) per population ranged from 7 to 39% and genetic differentiation between populations was ΦPT=0.790 (P<0.01). Genetic distances among populations (0.135–0.426) correlated significantly with geographical distances (r=0.183; P<0.008). Populations in overmoistured soil contained higher % P (28.3) when compared to drier soil (18.7; P<0.05). All recorded populations were close to roads; their % P did not depend on proximity to buildings, light intensity or population size. Our RAPD analyses indicate multiple introductions of this species in Lithuania. Analyses of I. parviflora at SSR and RAPD loci show that the invasion process is reflected in genetic structure.  相似文献   

9.
In this work we assessed the genetic diversity of 32 C.?calceolus populations from Poland. Mean genetic diversity was moderate (P?=?36.4%, A?=?1.58, H O?=?0.143, F IS?=?0.059), and seven geographic regions did not differ significantly in their levels of polymorphism (p?>?0.05), although allele frequencies varied greatly. Only four unique alleles were found, at three sites in southern and southeastern Poland. Genetic (P, A) and genotypic diversity parameters (G, G U) were significantly correlated with population size (p?<?0.001). In the 32 studied populations we separated 422 different multilocus genotypes; none was common to all populations. Overall population differentiation was moderate at 0.137 (p?<?0.001), but we found a significant pattern of isolation by distance for the whole dataset (r 2?=?0.65, p?<?0.001). Our chloroplast DNA (cpDNA) results suggest a single evolutionary lineage and a common origin for all Polish C.?calceolus populations. Information about the genetic health of C.?calceolus populations should be useful in developing conservation strategies.  相似文献   

10.
Two experiments involving 144 Yorkshire × Lacombe gilts, with an average initial weight of 20 kg, were conducted. In Experiment 1 the gilts were allotted to a control diet containing soya bean meal (SBM) or to diets in which either 50% or all of the supplementary protein was provided by Tower rapeseed meal (RSM). In the second experiment the two diets had either SBM or Tower RSM as the supplementary protein source. In a third diet Tower RSM was supplemented with sufficient lysine to equal the calculated available lysine level of the SBM control diet. In Experiment 1, gilts given the SBM diet grew from 20 to 60 kg significantly faster (P<0.01), and had better feed conversion efficiency (P<0.01), than those given the RSM diets. A 50% replacement of SBM by Tower RSM gave intermediate results. Partial or total replacement of SBM by Tower did not significantly affect the growth rate or feed conversion efficiency of the gilts when growing from 60 to 100 kg liveweight. Serum triiodothyronine (T3) and thyroxine (T4) concentrations of the gilts at 100 kg were lower in pigs fed on the RSM diets but the differences were not significant. In the second experiment, total replacement of SBM by Tower RSM, with or without the addition of lysine, significantly (P<0.001) reduced growth rate and feed conversion efficiency during the growing period (20–60 kg) but did not significantly affect performance during the finishing period (60–90 kg). Serum T3 concentration was not significantly affected by the addition of Tower RSM to the diet but T4 concentrations were significantly reduced (P<0.01). None of the carcass parameters studied were significantly affected by the addition of Tower RSM to the diets.  相似文献   

11.
Hormonal changes during early neonatal life play a major role in the physiological processes underlying the maturation of several organs. Since prostaglandins and cortisol are associated with fetal organ system maturation, the aim of this study was to evaluate 15-ketodihydro-PGF (PGM) and cortisol plasma concentrations during the first 21 days after birth in foals born by either spontaneous (24 foals) or low-dose oxytocin (OT)-induced parturition performed after at least 320 gestational days (25 foals) since induction is often considered to be a cause of prematurity. After spontaneous birth, the PGM concentration was significantly (P < 0.05) higher at 20 and 30 min compared to samples taken several hours or days later, while induced foals showed significantly (P < 0.05) higher concentrations at 10, 20, and 30 min. Regarding differences between the two groups, the plasma concentration of PGM was significantly higher 10 (P < 0.01), 20 (P < 0.05), and 30 (P < 0.05) min and 3 h (P < 0.05) after birth in induced foals compared to foals born by spontaneous parturition. It is difficult to determine whether the higher initial PGM concentrations in induced foals is related to higher uterine or fetal PGM release induced by exogenous OT stimulation. Cortisol plasma levels in both groups were higher at birth (P < 0.05) compared to the later sampling times. No differences were observed between the two groups indicating that the induction protocol used does not seem to result in premature foals.  相似文献   

12.
A series of trials were conducted to study the effect of either nitrogen source or supply pattern on the growth, rumen fermentation pattern and utilisation of straw by Ethiopian Menz sheep. All experimental sheep were given teff straw basal diet (CON). Irrespective of the trial, treatment sheep were offered either cottonseed cake (CSC), leucaena (LEU) and sesbania (SESM) in the morning prior to teff straw. Additional treatments with sesbaia were offered either in the evening (SESE) or morning and evening (SESME). Measurements included roughage intake, digestibility, kinetics, rumen fermentation patterns, nitrogen utilisation, microbial protein supply and growth of sheep.Rate of degradation was highest (P < 0.05) when sesbania was offered once a day compared with twice a day, while supplementation produced higher (P < 0.05) liquid passage rates. Diets with sesbania produced higher (P < 0.05) roughage intake compared with leucaena. Microbial protein supply as well as N economy were similar (P > 0.05) among the foliage diets irrespective of source, time or frequency of feeding. Supplementation enhanced (P < 0.001) growth rates in sheep, while cottonseed cake (CSC) diet was superior (P < 0.01) to the fodder trees. Growth rates declined across treatments during the second phase (6–10 weeks) compared with the initial period (1–6 weeks). It is also possible for farmers to feed sesbania supplements in the morning or evening or twice daily without any detrimental effects.  相似文献   

13.
The aims of this study were to assess the seasonal population dynamics and evaluate the performance of Apis mellifera jemenitica (local bee) and introduced hybrid honeybee colonies in the lowlands and highlands of southwestern Saudi Arabia. Data regarding the performance and population dynamics parameters such as brood and adult bee population, amounts of stored pollen and nectar were gathered from the two races (25 colonies of each) for one year (April 2013 through March 2014), and statistically tested. The results indicated that at low lands, local bee colonies maintained relatively high brood and adult bee populations (P < 0.05) than introduced honeybee colonies and produced more (P < 0.05) honey. The local bee colonies were able to hoard three times more (P < 0.05) pollen and built more (P < 0.05) queen cells than introduced bees in both the low and highland areas. The annual survival rate of local bee colonies was almost double (P < 0.05) than that of introduced honeybee colonies. Moreover, local bees had greater (P < 0.05) adult bee and brood populations than imported, throughout the year. The relatively good performance of local colonies could be due to their long year’s adaptation to cope with resource scarcity and unpredictable environmental conditions of the regions. The possible reasons for the dwindling of the imported hybrid colonies could be due to continuing to exhibit adaptive characteristics of their original that might not fit well with the new environment.  相似文献   

14.
The typical desert-inhabiting shrub Haloxylon ammodendron (C. A. Mey.) Bunge is an important species that is endangered in Northwest China. In this study, variance, correlation and cluster analysis were employed to examine phenotypic variations of H. ammodendron seed traits from 14 populations in China to investigate their relationships with environmental and genetic factors. The average coefficient of variation was higher among regions (26.9%) than within regions (19.8%). Correlation analysis revealed that the diameter/thickness and fruit wing length were significantly correlated with environmental factors. A cluster dendrograms designed based on seed traits was consistent with the finding from environmental and genetic data obtained using Ward's method and the unweighted pair-group method with arithmetic means. A Mantel test revealed correlation between seed traits and environmental data (r = 0.53, P < 0.01) was greater than that between seed traits and genetic data (r = 0.25, P < 0.05). Thus, seed traits associated with morphology, mass, and germination varied significantly among the populations, are strongly affected by climatic and geographical factors, and were moderately correlated with genetic diversity. These results provide insights for designing appropriate conservation strategies for H. ammodendron.  相似文献   

15.
Jellyfish are of particular concern for marine finfish aquaculture. In recent years repeated mass mortality episodes of farmed fish were caused by blooms of gelatinous cnidarian stingers, as a consequence of a wide range of hemolytic, cytotoxic, and neurotoxic properties of associated cnidocytes venoms. The mauve stinger jellyfish Pelagia noctiluca (Scyphozoa) has been identified as direct causative agent for several documented fish mortality events both in Northern Europe and the Mediterranean Sea aquaculture farms. We investigated the effects of P. noctiluca envenomations on the gilthead sea bream Sparus aurata by in vivo laboratory assays. Fish were incubated for 8 hours with jellyfish at 3 different densities in 300 l experimental tanks. Gill disorders were assessed by histological analyses and histopathological scoring of samples collected at time intervals from 3 hours to 4 weeks after initial exposure. Fish gills showed different extent and severity of gill lesions according to jellyfish density and incubation time, and long after the removal of jellyfish from tanks. Jellyfish envenomation elicits local and systemic inflammation reactions, histopathology and gill cell toxicity, with severe impacts on fish health. Altogether, these results shows P. noctiluca swarms may represent a high risk for Mediterranean finfish aquaculture farms, generating significant gill damage after only a few hours of contact with farmed S. aurata. Due to the growth of the aquaculture sector and the increased frequency of jellyfish blooms in the coastal waters, negative interactions between stinging jellyfish and farmed fish are likely to increase with the potential for significant economic losses.  相似文献   

16.
17.
The concentration of acid soluble carnitine was determined in several body tissues and fluids in rats under various conditions of sex steroid regulation. Intact female rats had significantly greater liver carnitine concentrations and urinary excretion rates, and lower blood plasma and heart carnitine concentrations than intact male rats. Ovariectomy increased blood plasma carnitine concentrations (P < 0.01) and the excretion of carnitine in the urine (P < 0.05). The administration of either estradiol or testosterone to ovariectomized rats did not alter blood plasma concentrations or urinary excretion of carnitine. Orchidectomized rats had similar blood plasma carnitine concentrations when compared to intact males but excreted significantly (P < 0.01) greater quantities of carnitine in their urine. Administration of testosterone to orchidectomized rats reduced (P < 0.01), whereas estradiol stimulated (P < 0.05) the excretion rate of carnitine in the urine; however, blood plasma carnitine concentrations were not affected by these hormones. These data suggest that a major site for modulation of body carnitine concentration in the male resides in the control of kidney excretion by androgens. Liver, heart and skeletal muscle carnitine concentrations were not altered by the administration of either estradiol or testosterone to orchidectomized or ovariectomized rats.  相似文献   

18.
We investigated the effects of pH on movement behaviors of the harmful algal bloom causing raphidophyte Heterosigma akashiwo. Motility parameters from >8000 swimming tracks of individual cells were quantified using 3D digital video analysis over a 6-h period in 3 pH treatments reflecting marine carbonate chemistry during the pre-industrial era, currently, and the year 2100. Movement behaviors were investigated in two different acclimation-to-target-pH conditions: instantaneous exposure and acclimation of cells for at least 11 generations. There was no negative impairment of cell motility when exposed to elevated PCO2 (i.e., low pH) conditions but there were significant behavioral responses. Irrespective of acclimation condition, lower pH significantly increased downward velocity and frequency of downward swimming cells (p < 0.001). Rapid exposure to lower pH resulted in 9% faster downward vertical velocity and up to 19% more cells swimming downwards (p < 0.001). Compared to pH-shock experiments, pre-acclimation of cells to target pH resulted in ~30% faster swimming speed and up to 46% faster downward velocities (all p < 0.001). The effect of year 2100 PCO2 levels on population diffusivity in pre-acclimated cultures was >2-fold greater than in pH-shock treatments (2.2 × 105 μm2 s−1 vs. 8.4 × 104 μm2 s−1). Predictions from an advection-diffusion model, suggest that as PCO2 increased the fraction of the population aggregated at the surface declined, and moved deeper in the water column. Enhanced downward swimming of H. akashiwo at low pH suggests that these behavioral responses to elevated PCO2 could reduce the likelihood of dense surface slick formation of H. akashiwo through reductions in light exposure or growth independent surface aggregations. We hypothesize that the HAB alga's response to higher PCO2 may exploit the signaling function of high PCO2 as indicative of net heterotrophy in the system, thus indicative of high predation rates or depletion of nutrients.  相似文献   

19.
Fatty acid translocase (FAT/CD36) is a membrane receptor that facilitates long-chain fatty acid uptake. To investigate its role in the regulation of long-chain fatty acid composition in muscle tissue, we studied and compared FAT/CD36 gene expression in muscle tissues of commercial broiler chickens and Chinese local Silky fowls. The results from gas chromatography–mass spectrometry analysis of muscle samples demonstrated that Chinese local Silky fowls had significantly higher (P < 0.05) proportions of linoleic acid (LA) and palmitic acid, lower proportions (P < 0.05) of arachidonic acid (AA) and oleic acid than the commercial broiler chickens. The mRNA expression levels of fatty acid (FA) transporters (FA transport protein-1, membrane FA-binding protein, FAT/CD36 and caveolin-1) in the m. ipsilateral pectoralis and biceps femoris were analyzed by Q-PCR, and FAT/CD36 expression levels showed significant differences between these types of chickens (P < 0.01). Interestingly, the levels of FAT/CD36 expression are positively correlated with LA content (r = 0.567, P < 0.01) but negatively correlated with palmitic acid content (r = −0.568, P < 0.01). Further experiments in the stably transfected Chinese hamster oocytes cells with chicken FAT/CD36 cDNA demonstrated that overexpression of FAT/CD36 improves total FA uptake with a significant increase in the proportion of LA and AA, and a decreased proportion of palmitic acid. These results suggest that chicken FAT/CD36 may selectively transport LA and AA, which may lead to the higher LA deposition in muscle tissue.  相似文献   

20.
《Endocrine practice》2021,27(4):286-290
ObjectiveCurrently, there are limited markers to predict the osteoporosis probability in patients with primary hyperparathyroidism. We studied the relationship between various parameters and results of DXAs at various skeletal sites.MethodsRetrospective review of data for 218 patients with primary hyperparathyroidism was performed. Age, BMI, bone mineral density, serum total calcium, ionized calcium, intact parathyroid hormone, albumin, alkaline phosphatase, phosphate, 25-hydroxy vitamin D, 1,25-dihydroxy vitamin D, 24-hour urinary calcium levels and parathyroid tumor weight were analyzed. Two different statistical models- linear regression and multivariate logistic regression were performed.ResultsAt the lumbar spine, with the linear model, BMI (P < .001), alkaline phosphatase (P < .001), and ionized calcium (P < .001) significantly correlated with T scores; whereas with the logistic model, BMI was the only variable predicting osteoporosis probability.At the femoral neck, BMI (P < .022), 25-hydroxy vitamin D (P < .001), 1,25-dihydroxy vitamin D (P < .034) correlated with T scores; whereas both BMI (P < .029) and age (P < .051) were the significant variables that predicted osteoporosis.At the total hip, BMI (P < .001) and age (P < .001) correlated with T scores; whereas with the logistic model, only BMI (P < .016) predicted osteoporosis. At the forearm, a model could not be generated due to limited number.ConclusionIn patients with primary hyperparathyroidism, BMI strongly correlated with T scores and probability of osteoporosis.  相似文献   

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