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61.
Ecological correlates of hind-limb length in the Carnivora 总被引:1,自引:0,他引:1
What determines the lengths and proportions of mammalian limbs? While the answer to this question is still largely unknown, a number of workers have recently begun analysing the selection of morphology in a rigorous framework, searching for quantitative links between structure, performance, and their ecological and behavioural context. The present study investigates a variety of ecological and behavioural variables to determine whether or not they are correlated with hind-limb length in the Carnivora. Data were analysed by using phylogenetically independent contrasts and phylogenetic analysis of covariance. We found that traditional perceptions of limb length are often inaccurate; some species widely regarded as relatively long-legged actually have limb lengths near those expected for their body size. Interestingly, relative hind-limb length is not a significant predictor of distance moved daily, home-range area, or prey size. Phylogenetic ANCOVA results, however, indicate a relationship between prey-capture behaviour and relative hind-limb length. These findings suggest that the evolution of carnivoran limb length has been most influenced by selection for prey-capture behaviour. These results, coupled with those of other studies, can be used to suggest which performance variables could most fruitfully be studied in the laboratory to understand the selection of the structure of the mammalian limb. We suggest that relevant performance variables might be: maximum jump height and/or length, the ability to generate outforces, and levels of stress tolerance in limb bones during prey pursuit/capture. 相似文献
62.
Posttetanic potentiation of human dorsiflexors 总被引:2,自引:0,他引:2
O'Leary, Deborah D., Karen Hope, and Digby G. Sale.Posttetanic potentiation of human dorsiflexors.J. Appl. Physiol. 83(6):2131-2138, 1997.Twitch contractions of the ankle dorsiflexors were evoked before and after applied 7-s tetanic stimulation at 100 Hzin 20 young adults. Torque decreased 15% during the tetanus. At 5 safter tetanus, twitch peak torque had potentiated 45%. Potentiationdeclined to 28% after 1 min, rose slightly to 33% at 2 min, anddeclined slowly with potentiation still 25% after 5 min. There waslarge intersubject variation in the amount of potentiation(5-140%) and its persistence (5 to 20 min). The muscle compoundaction potential (M wave) did not change significantly (from pretetanicvalue) at 5 s after tetanus but increased sharply (26%) at 2 min andthen subsided. Twitch half relaxation time (23%) decreasedsignificantly more than twitch rise time (13%) 5 s after tetanus andrecovered more slowly. Twitch rates of torque development (75%) andrelaxation (71%) increased similarly 5 s after tetanus and were stillelevated (~25%) at 5 min. The extent of twitch torque potentiationwas significantly inversely correlated with pretetanic twitch rise time(r = 0.69), half relaxation time (r = 0.61), andtwitch-to-tetanus ratio (r = 0.66). The data indicate that posttetanic potentiation has agreater effect on twitch half relaxation time than on time to peaktorque and is more prominent in muscles with a short twitch time courseand small twitch-to-tetanus ratio. 相似文献
63.
Dr. Mark E. McKinney Karen Rovang Dr. James C. Buell Dr. Robert S. Eliot 《Applied psychophysiology and biofeedback》1984,9(3):365-370
Impedance cardiography (ZCG), a noninvasive technique used to determine stroke volume and ventricular performance, is currently being utilized more extensively in psychophysiological research and may also prove a useful tool in the control of hypertension. To date, most studies employing ZCG have tested male subjects or patients. However, women and men differ on two important parameters used to calculate stroke volume: thoracic impedance (Zo), and the first derivative of change in impedance over time (dZ/dtmin). Examination of the clinical records of 19 females and 19 males, all nonmedicated, indicated that women had higher Zo levels (F(1, 36)=46.2,p<.0001) and higher dZ/dtmin levels (F(1, 36)=51.8, p<.0001), although calculated stroke volume indexes did not differ. A second sample of 10 women and 8 men, all healthy and nonmedicated, confirmed these findings. The differences in Zo are not due entirely to sex differences in height, weight, percent body fat, and subscapula skin-fold thickness, although these factors differ across sexes. It is important for researchers and clinicians utilizing ZCG with female subjects to be aware of these differences. 相似文献
64.
We have examined the shape and distribution of clathrin-coated pits in Swiss 3T3 cells at 4 or 37 degrees C using electron microscopy with serial sections and immunofluorescence light microscopy. Both groups were fixed in glutaraldehyde and preserved further using a membrane contrast enhancement technique consisting of sequential osmium-ferrocyanide, thiocarbohydrazide and osmium-ferrocyanide treatment in situ. Concanavalin A-horseradish peroxidase (conA-HRP) was used to identify these structures participating in endocytosis. Two hundred twenty-two clathrin-coated structures were analysed; 126 from cells fixed at 4 degrees C, and 96 from cells fixed after a 3 min warm-up to 37 degrees C. All coated structures labeled with conA-HRP had demonstrable connections to the plasma membrane. These coated structures were morphologically classified into three categories: (a) flat pits; (b) curved pits; and (c) pits with narrow-neck connections to the plasma membrane. At 37 degrees C, 27% of coated pits had narrow neck connections to the plasma membrane whereas at 4 degrees C only 1% had such connections. Receptosomes (endosomes) labeled with conA-HRP were found only after incubation at 37 degrees C, indicating that active endocytosis was occurring in cells at 37 degrees C, but not at 4 degrees C. Immunofluorescence with anti-clathrin antibody was used to quantitate the number of clathrin-coated pits in Swiss 3T3 cells incubated at 4 and 37 degrees C prior to fixation. No difference was detected. There were 426 +/- 122 pits per cell at 37 degrees C and 441 +/- 106 at 4 degrees C. These results support the hypothesis that formation of a narrow neck connected a coated pit to the cell surface is an early step in the mechanism of receptor-mediated endocytosis. 相似文献
65.
Localized Photosynthate Deposition in Citrus Fruit Segments Relative to Source-Leaf Position 总被引:1,自引:0,他引:1
Photosynthate translocation into fruit segments was examinedin Pineapple sweet orange Citrus sinensis (L.)Osbeck to determine whether previously reported patterns ofdistribution [Koch (1984) HortScience 19: 260] would changeover time or with alterations in balance between source leavesand sink fruit. In control plants, 14CO2 was supplied to a sourceleaf nearest the fruit for 1 h, followed by 5 h translocation.Over 89% of [14C]assimilates in the fruit were localized in4 segments directly aligned with the source and 73% of thesewere in the center 2 segments. Peel, pulp and seeds showed similarpatterns. Little or no lateral spreading of [14C]photosynthatesoccurred when an additional 7 days were allowed for translocation,but distribution was slightly broader when the source leaf was8 nodes farther from the fruit. Defoliation and girdling toreduce the source/sink ratio gave variable results if done 18h before experiments, but widened the area receiving [14C]assimilatesto approximately half the fruit if done 7 days earlier. Thisoccurred only when an entire fruit, was dependent upon a singlesource, leaving the opposite half fruit without an externalsupply of photosynthates. These data show an extreme degreeof preferential translocation and inflexibility which can occurin a transport path.
1Supported by United States Department of Agriculture CompetitiveResearch Grant 59-2121-1-1-752-0, Regional Project NC-142, andthe Institute of Food and Agricultural Sciences, Universityof Florida. (Received January 12, 1984; Accepted May 14, 1984) 相似文献
66.
Summary X-inactivation patterns were studied by replication analyses both in lymphocytes and skin fibroblasts of two patients carrying balanced X-autosome translocations, t(X;10)-(pter;q11) and t(X;17)(q11;q11), and one patient with an unbalanced translocation t(X;22)(p21;q11). Preferential late replication of the normal X chromosome was found in lymphocytes of both patients carrying balanced translocations and in skin fibroblasts of the patient carrying the translocation t(X;17). However, skin fibroblasts of the patient with a translocation t(X;10) showed preferential late replication of the abnormal der(X) chromosome with no spreading of late replication to the autosomal segment. In the case of unbalanced translocation t(X;22) there was preferential late replication of the der(X) chromosome both in lymphocytes and skin fibroblasts. The abnormal phenotype of the patients is discussed in relation to the observed X-inactivation patterns and the variability of the patterns in different tissues. 相似文献
67.
68.
69.
Robert L. Trelstad Karen R. Lawley 《Biochemical and biophysical research communications》1977,76(2):376-384
Neutral solutions of pepsin extracted human collagens derived from glomeruli, kidney, aorta, lung, heart, bowel, spleen, skeletal muscle and skin were subjected to heat gelation at 37°C. Centrifugation of the gel provided two fractions: gelled pellet and non-gelled supernatant. Analysis of these two fractions by gel electrophoresis, molecular sieve and ion exchange chromatography, and amino acid and carbohydrate determinations indicated that the non-gelled supernatant contained a substantial enrichment of basement membrane like collagen. The initial characterization of lung derived basement membrane collagen indicated close similarities with those derived from glomeruli and whole kidney and differences with that obtained from the spleen. 相似文献
70.
Summary The degree of association between cattle egrets (Bubulcus ibis) and cattle was studied during one summer on Saint Catherines Island, Georgia, USA. Previous work by Grubb (1976) and others indicated that cattle egrets foraging with cattle require fewer steps and less time to catch prey than egrets foraging without cattle and single egrets catch prey at a higher rate than egrets foraging in groups of two or more with cattle. Accordingly, we predicted that when given a choice egrets should forage with cattle rather than alone, egrets should prefer to associate with standing rather than sitting cattle, and single egrets associated with cattle should be more common than expected by chance.In excess of two-thirds of the egrets accompanied cattle. Neither time of day nor month influenced the degree of association, but egrets in forest were more likely to be associated with cattle than egrets in pasture. Standing cattle were more likely to be accompanied by egrets than were sitting cattle. Single egrets occurred more frequently than expected by chance when accompanying standing cattle but not when associated with sitting cattle. Thus, cattle egrets usually distributed themselves among cattle in the way predicted by optimal foraging theory.We dedicate this paper to the memory of Michael D. Sabath 相似文献