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MT Butcher JW Hermanson NG Ducharme LM Mitchell LV Soderholm JE Bertram 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2009,152(1):100-114
The forelimb digital flexors of the horse display remarkable diversity in muscle architecture despite each muscle-tendon unit having a similar mechanical advantage across the fetlock joint. We focus on two distinct muscles of the digital flexor system: short compartment deep digital flexor (DDF(sc)) and the superficial digital flexor (SDF). The objectives were to investigate force-length behavior and work performance of these two muscles in vivo during locomotion, and to determine how muscle architecture contributes to in vivo function in this system. We directly recorded muscle force (via tendon strain gauges) and muscle fascicle length (via sonomicrometry crystals) as horses walked (1.7 m s(-1)), trotted (4.1 m s(-1)) and cantered (7.0 m s(-1)) on a motorized treadmill. Over the range of gaits and speeds, DDF(sc) fascicles shortened while producing relatively low force, generating modest positive net work. In contrast, SDF fascicles initially shortened, then lengthened while producing high force, resulting in substantial negative net work. These findings suggest the long fibered, unipennate DDF(sc) supplements mechanical work during running, whereas the short fibered, multipennate SDF is specialized for economical high force and enhanced elastic energy storage. Apparent in vivo functions match well with the distinct architectural features of each muscle. 相似文献
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JW Arntzen 《Frontiers in zoology》2006,3(1):1-11
Background
The two sympatric species of Tunisian desert ants, Cataglyphis bicolor and C. mauritanica, do not exhibit any differences in their foraging ecology, e.g. in food preferences and in their spatial and temporal activity patterns. Here we show that instead the two species markedly differ in their life histories.Results
We analysed mtDNA of specimens that were collected along a 250-km transect. C. bicolor exhibited a genetically unstructured population (with the genetic and geographic distances among colonies not being correlated). On the contrary the populations of the polygynous C. mauritanica were clearly structured, i.e. exhibited a strong correlation between genetic and geographic distances. This difference is in accordance with large queen dispersal distances due to far-reaching mating flights in C. bicolor and small queen dispersal distances due to colony foundation by budding in C. mauritanica. Furthermore, wherever we found populations of both species to coexist within the same habitat, the habitat was used agriculturally. Mapping nest positions over periods of several years showed that plowing dramatically decreased the nest densities of either species.Conclusion
We conclude that owing to its greater queen dispersal potential C. bicolor might be more successful in quickly re-colonizing disturbed areas, while the slowly dispersing C. mauritanica could later out-compete C. bicolor by adopting its effective nest-budding strategy. According to this scenario the observed sympatry of the two species might be an intermediate stage in which faster colonization by one species and more powerful exploitation of space by the other species have somehow balanced each other out. In conclusion, C. bicolor and C. mauritanica represent an example where environmental disturbances in combination with different life histories might beget sympatry in congeneric species with overlapping niches. 相似文献195.
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Nagesh Ragavendra JW Ju James W Sayre Sharon Hirschowitz Inder Chopra Michael W Yeh 《Journal of biological engineering》2008,2(1):1-4
Background
Human solid tumors that are hard or firm on physical palpation are likely to be cancerous, a clinical maxim that has been successfully applied to cancer screening programs, such as breast self-examination. However, the biological relevance or prognostic significance of tumor hardness remains poorly understood. Here we present a fracture mechanics based in vivo approach for characterizing the fracture toughness of biological tissue of human thyroid gland tumors.Methods
In a prospective study, 609 solid thyroid gland tumors were percutaneously probed using standard 25 gauge fine needles, their tissue toughness ranked on the basis of the nature and strength of the haptic force feedback cues, and subjected to standard fine needle biopsy. The tumors' toughness rankings and final cytological diagnoses were combined and analyzed. The interpreting cytopathologist was blinded to the tumors' toughness rankings.Results
Our data showed that cancerous and noncancerous tumors displayed remarkable haptically distinguishable differences in their material toughness.Conclusion
The qualitative method described here, though subject to some operator bias, identifies a previously unreported in vivo approach to classify fracture toughness of a solid tumor that can be correlated with malignancy, and paves the way for the development of a mechanical device that can accurately quantify the tissue toughness of a human tumor. 相似文献197.
EDWARD J. GREGR LINDA M. NICHOL JANE C. WATSON JOHN K. B. FORD GRAEME M. ELLIS 《The Journal of wildlife management》2008,72(2):382-388
ABSTRACT We estimated carrying capacity for sea otters (Enhydra lutris) in the coastal waters of British Columbia, Canada, by characterizing habitat according to the complexity of nearshore intertidal and sub-tidal contours. We modeled the total area of complex habitat on the west coast of Vancouver Island by first calculating the complexity of the Checleset Bay-Kyuquot Sound (CB-KS) region, where sea otters have been at equilibrium since the mid-1990s. We then identified similarly complex areas on the west coast of Vancouver Island (WCVI model), and adapted the model to identify areas of similar complexity along the entire British Columbia coast (BC model). Using survey data from the CB-KS region, we calculated otter densities for the habitat predicted by the 2 models. The density estimates for CB-KS were 3.93 otters/km2 and 2.53 otters/km2 for the WCVI and BC models, respectively, and the resulting 2 estimates of west coast of Vancouver Island complex habitat carrying capacity were not significantly different (WCVI model: 5,123, 95% CI = 3,337–7,104; BC model: 4,883, 95% CI = 3,223–6,832). The BC model identified the region presently occupied by otters on the central British Columbia coast, but the amount of coast-wide habitat it predicted (5,862 km2) was relatively small, and the associated carrying capacity estimate (14,831, 95% CI = 9,790–20,751) was low compared to historical accounts. We suggest that our model captured a type of high-quality or optimum habitat prevalent on the west coast of Vancouver Island, typified by the CB-KS region, and that suitable sea otter habitat elsewhere on the coast must include other habitat characteristics. We therefore calculated a linear, coast-wide carrying capacity of 52,459 sea otters (95% CI = 34,264–73,489)—a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species. 相似文献
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ELLIS ERLE C.; TURGEON ROBERT; SPANSWICK ROGER M. 《Journal of experimental botany》1992,43(9):1235-1241
Photosynthate unloading in Phaseolus vulgaris L. seed coatswas studied by treating perfused seed coats with differing concentrationsof an osmoticum and ethylenediaminetetraacetate (EDTA). Largechanges in osmoticum concentration typically produced rapidchanges in efflux of unlabelled sugar and steady-state-labelled14C-photosynthate. Osmoticum-induced changes in photosynthateefflux were caused by phloem import stimulation at low cellturgor and net efflux stimulation by high cell turgor. Eventhough rapid changes in sugar and tracer efflux were often inducedby osmoticum treatments, the specific activity of sugar releasedfrom seed coats was not greatly affected by these treatmentsand was similar to the specific activity of sugar remainingin the seed coat after perfusion. Thus, tracer was transportedfrom the phloem throughout the seed coat sugar pool before itwas released to the apoplast. This result is most consistentwith symplastic phloem unloading throughout perfused seed coats,because apoplastic transport between cells within the seed coatwas blocked by perfusion. Photosynthate efflux was stimulatedby simultaneous treatment of seed coats with EDTA and differentconcentrations of an osmoticum; loss of photosynthate from seedcoats did not appear to be tissue-specific. Key words: Phaseolus vulgaris, seed coat, photosynthate unloading, turgor, EDTA 相似文献