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Douglas A Syme - One of the best experts on this subject based on the ideXlab platform.
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Effects of temperature on power output and contraction kinetics in the locomotor muscle of the regionally endothermic common thresher shark (Alopias vulpinus).
Fish physiology and biochemistry, 2012Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Douglas A Syme, Scott A. Aalbers, David G. Mcgillivray, Diego BernalAbstract:The common thresher shark (Alopias vulpinus) is a pelagic species with medially positioned red aerobic swimming musculature (RM) and regional RM endothermy. This study tested whether the contractile characteristics of the RM are functionally similar along the length of the body and assessed how the contractile properties of the common thresher shark compare with those of other sharks. Contractile properties of the RM were examined at 8, 16 and 24 °C from anterior and posterior axial positions (0.4 and 0.6 fork length, respectively) using the work loop technique. Experiments were performed to determine whether the contractile properties of the RM are similar along the body of the common thresher shark and to document the effects of temperature on muscle power. Axial differences in contractile properties of RM were found to be small or absent. Isometric twitch kinetics of RM were ~fivefold slower than those of white muscle, with RM twitch durations of about 1 s at 24 °C and exceeding 5 s at 8 °C, a Q10 of nearly 2.5. Power increased approximately tenfold with the 16 °C increase in temperature, while the Cycle Frequency for maximal power only increased from about 0.5–1.0 Hz over this temperature range. These data support the hypothesis that the RM is functionally similar along the body of the common thresher shark and corroborate previous findings from shark species both with and without medial RM. While twitch kinetics suggest the endothermic RM is not unusually temperature sensitive, measures of power suggest that the RM is not well suited to function at cool temperatures. The Cycle Frequency at which power is maximized appeared relatively insensitive to temperature in RM, which may reflect the relatively cooler temperature of the thresher RM compared to that observed in lamnid sharks as well as the relatively slow RM phenotype in these large fish.
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thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard shark and shortfin mako shark
The Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard shark Triakis semifasciata and endothermic shortfin mako shark Isurus oxyrinchus . The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25°C for Triakis and 15 to 28°C for Isurus at Cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6–0.65 L ) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in mako sharks at unphysiologically cool temperatures (<20°C). We found no significant differences in optimal stimulus duration, phase, net work or power output between anterior and posterior bundles in each species. With increasing Cycle Frequency the stimulus duration yielding maximum power decreased while optimal phase occurred earlier. The Cycle Frequency at which peak power was generated in leopard shark RM was only affected slightly by temperature, increasing from about 0.6 to 1.0 Hz between 15 and 25°C. In contrast, mako RM showed a much more dramatic temperature sensitivity, with the peak power Frequency rising from <0.25 to 2.25 Hz between 15 and 28°C. These data support the hypothesis that the contractile properties of RM are functionally similar along the body in both species. In addition, our data identify a significant difference in the effect of temperature on net work and power output between these two shark species; at 15°C muscle from the ectothermic leopard shark performs relatively well in comparison with mako, while at higher temperatures, which reflect those normally experienced by the mako, the optimal Cycle Frequency for power is nearly double that of the leopard shark, suggesting that the mako may be able to maintain greater aerobic swimming speeds.
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thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard shark and shortfin mako shark
The Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard shark Triakis semifasciata and endothermic shortfin mako shark Isurus oxyrinchus. The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25 degrees C for Triakis and 15 to 28 degrees C for Isurus at Cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6-0.65 L) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in mako sharks at unphysiologically cool temperatures (<20 degrees C). We found no significant differences in optimal stimulus duration, phase, net work or power output between anterior and posterior bundles in each species. With increasing Cycle Frequency the stimulus duration yielding maximum power decreased while optimal phase occurred earlier. The Cycle Frequency at which peak power was generated in leopard shark RM was only affected slightly by temperature, increasing from about 0.6 to 1.0 Hz between 15 and 25 degrees C. In contrast, mako RM showed a much more dramatic temperature sensitivity, with the peak power Frequency rising from <0.25 to 2.25 Hz between 15 and 28 degrees C. These data support the hypothesis that the contractile properties of RM are functionally similar along the body in both species. In addition, our data identify a significant difference in the effect of temperature on net work and power output between these two shark species; at 15 degrees C muscle from the ectothermic leopard shark performs relatively well in comparison with mako, while at higher temperatures, which reflect those normally experienced by the mako, the optimal Cycle Frequency for power is nearly double that of the leopard shark, suggesting that the mako may be able to maintain greater aerobic swimming speeds.
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effects of longitudinal body position and swimming speed on mechanical power of deep red muscle from skipjack tuna katsuwonus pelamis
The Journal of Experimental Biology, 2002Co-Authors: Douglas A Syme, Robert E ShadwickAbstract:SUMMARY The mechanical power output of deep, red muscle from skipjack tuna ( Katsuwonus pelamis ) was studied to investigate (i) whether this muscle generates maximum power during cruise swimming, (ii) how the differences in strain experienced by red muscle at different axial body locations affect its performance and (iii) how swimming speed affects muscle work and power output. Red muscle was isolated from approximately mid-way through the deep wedge that lies next to the backbone; anterior (0.44 fork lengths, ANT) and posterior (0.70 fork lengths, POST) samples were studied. Work and power were measured at 25°C using the work loop technique. Stimulus phases and durations and muscle strains (±5.5 % in ANT and ±8 % in POST locations) experienced during cruise swimming at different speeds were obtained from previous studies and used during work loop recordings. In addition, stimulus conditions that maximized work were determined. The stimulus durations and phases yielding maximum work decreased with increasing Cycle Frequency (analogous to tail-beat Frequency), were the same at both axial locations and were almost identical to those used by the fish during swimming, indicating that the muscle produces near-maximal work under most conditions in swimming fish. While muscle in the posterior region undergoes larger strain and thus produces more mass-specific power than muscle in the anterior region, when the longitudinal distribution of red muscle mass is considered, the anterior muscles appear to contribute approximately 40 % more total power. Mechanical work per length Cycle was maximal at a Cycle Frequency of 2–3 Hz, dropping to near zero at 15 Hz and by 20–50 % at 1 Hz. Mechanical power was maximal at a Cycle Frequency of 5 Hz, dropping to near zero at 15 Hz. These fish typically cruise with tail-beat frequencies of 2.8–5.2 Hz, frequencies at which power from cyclic contractions of deep red muscles was 75–100 % maximal. At any given Frequency over this range, power using stimulation conditions recorded from swimming fish averaged 93.4±1.65 % at ANT locations and 88.6±2.08 % at POST locations (means ± s.e.m., N =3–6) of the maximum using optimized conditions. When Cycle Frequency was held constant (4 Hz) and strain amplitude was increased, work and power increased similarly in muscles from both sample sites; work and power increased 2.5-fold when strain was elevated from ±2 to ±5.5 %, but increased by only approximately 12 % when strain was raised further from ±5.5 to ±8 %. Taken together, these data suggest that red muscle fibres along the entire body are used in a similar fashion to produce near-maximal mechanical power for propulsion during normal cruise swimming. Modelling suggests that the tail-beat Frequency at which power is maximal (5 Hz) is very close to that used at the predicted maximum aerobic swimming speed (5.8 Hz) in these fish.
Iourii Manovskii - One of the best experts on this subject based on the ideXlab platform.
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the cyclical behavior of equilibrium unemployment and vacancies revisited
The American Economic Review, 2008Co-Authors: Marcus Hagedorn, Iourii ManovskiiAbstract:Recently, a number of authors have argued that the standard search model cannot generate the observed business-Cycle-Frequency fluctuations in unemployment and job vacancies, given shocks of a plausible magnitude. We propose a new calibration strategy of the standard model that uses data on the cost of vacancy creation and cyclicality of wages to identify the two key parameters - the value of nonmarket activity and the bargaining weights. Our calibration implies that the model is consistent with the data.
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the cyclical behavior of equilibrium unemployment and vacancies revisited
Social Science Research Network, 2008Co-Authors: Marcus Hagedorn, Iourii ManovskiiAbstract:Recently, a number of authors have argued that the standard search model cannot generate the observed business-Cycle-Frequency fluctuations in unemployment and job vacancies, given shocks of a plausible magnitude. We use data on the cost of vacancy creation and cyclicality of wages to identify the two key parameters of the model - the value of non-market activity and the bargaining weights. Our calibration implies that the model is, in fact, consistent with the data.
Robert E Shadwick - One of the best experts on this subject based on the ideXlab platform.
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work loop dynamics of the pigeon columba livia humerotriceps demonstrate potentially diverse roles for active wing morphing
The Journal of Experimental Biology, 2019Co-Authors: Jolan S Theriault, Robert E Shadwick, Joseph W Bahlman, Douglas L AltshulerAbstract:ABSTRACT Control of wing shape is believed to be a key feature that allows most birds to produce aerodynamically efficient flight behaviors and high maneuverability. Anatomical organization of intrinsic wing muscles suggests specific roles for the different motor elements in wing shape modulation, but testing these hypothesized functions requires challenging measurements of muscle activation and strain patterns, and force dynamics. The wing muscles that have been best characterized during flight are the elbow muscles of the pigeon ( Columba livia ). In vivo studies during different flight modes revealed variation in strain profile, activation timing and duration, and contractile Cycle Frequency of the humerotriceps, suggesting that this muscle may alter wing shape in diverse ways. To examine the multifunction potential of the humerotriceps, we developed an in situ work loop approach to measure how activation duration and contractile Cycle Frequency affected muscle work and power across the full range of activation onset times. The humerotriceps produced predominantly net negative power, likely due to relatively long stimulus durations, indicating that it absorbs work, but the work loop shapes also suggest varying degrees of elastic energy storage and release. The humerotriceps consistently exhibited positive and negative instantaneous power within a single contractile Cycle, across all treatments. When combined with previous in vivo studies, our results indicate that both within and across contractile Cycles, the humerotriceps can dynamically shift among roles of actuator, brake, and stiff or compliant spring, based on activation properties that vary with flight mode.
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thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard shark and shortfin mako shark
The Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard shark Triakis semifasciata and endothermic shortfin mako shark Isurus oxyrinchus . The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25°C for Triakis and 15 to 28°C for Isurus at Cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6–0.65 L ) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in mako sharks at unphysiologically cool temperatures (<20°C). We found no significant differences in optimal stimulus duration, phase, net work or power output between anterior and posterior bundles in each species. With increasing Cycle Frequency the stimulus duration yielding maximum power decreased while optimal phase occurred earlier. The Cycle Frequency at which peak power was generated in leopard shark RM was only affected slightly by temperature, increasing from about 0.6 to 1.0 Hz between 15 and 25°C. In contrast, mako RM showed a much more dramatic temperature sensitivity, with the peak power Frequency rising from <0.25 to 2.25 Hz between 15 and 28°C. These data support the hypothesis that the contractile properties of RM are functionally similar along the body in both species. In addition, our data identify a significant difference in the effect of temperature on net work and power output between these two shark species; at 15°C muscle from the ectothermic leopard shark performs relatively well in comparison with mako, while at higher temperatures, which reflect those normally experienced by the mako, the optimal Cycle Frequency for power is nearly double that of the leopard shark, suggesting that the mako may be able to maintain greater aerobic swimming speeds.
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thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard shark and shortfin mako shark
The Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard shark Triakis semifasciata and endothermic shortfin mako shark Isurus oxyrinchus. The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25 degrees C for Triakis and 15 to 28 degrees C for Isurus at Cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6-0.65 L) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in mako sharks at unphysiologically cool temperatures (<20 degrees C). We found no significant differences in optimal stimulus duration, phase, net work or power output between anterior and posterior bundles in each species. With increasing Cycle Frequency the stimulus duration yielding maximum power decreased while optimal phase occurred earlier. The Cycle Frequency at which peak power was generated in leopard shark RM was only affected slightly by temperature, increasing from about 0.6 to 1.0 Hz between 15 and 25 degrees C. In contrast, mako RM showed a much more dramatic temperature sensitivity, with the peak power Frequency rising from <0.25 to 2.25 Hz between 15 and 28 degrees C. These data support the hypothesis that the contractile properties of RM are functionally similar along the body in both species. In addition, our data identify a significant difference in the effect of temperature on net work and power output between these two shark species; at 15 degrees C muscle from the ectothermic leopard shark performs relatively well in comparison with mako, while at higher temperatures, which reflect those normally experienced by the mako, the optimal Cycle Frequency for power is nearly double that of the leopard shark, suggesting that the mako may be able to maintain greater aerobic swimming speeds.
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effects of longitudinal body position and swimming speed on mechanical power of deep red muscle from skipjack tuna katsuwonus pelamis
The Journal of Experimental Biology, 2002Co-Authors: Douglas A Syme, Robert E ShadwickAbstract:SUMMARY The mechanical power output of deep, red muscle from skipjack tuna ( Katsuwonus pelamis ) was studied to investigate (i) whether this muscle generates maximum power during cruise swimming, (ii) how the differences in strain experienced by red muscle at different axial body locations affect its performance and (iii) how swimming speed affects muscle work and power output. Red muscle was isolated from approximately mid-way through the deep wedge that lies next to the backbone; anterior (0.44 fork lengths, ANT) and posterior (0.70 fork lengths, POST) samples were studied. Work and power were measured at 25°C using the work loop technique. Stimulus phases and durations and muscle strains (±5.5 % in ANT and ±8 % in POST locations) experienced during cruise swimming at different speeds were obtained from previous studies and used during work loop recordings. In addition, stimulus conditions that maximized work were determined. The stimulus durations and phases yielding maximum work decreased with increasing Cycle Frequency (analogous to tail-beat Frequency), were the same at both axial locations and were almost identical to those used by the fish during swimming, indicating that the muscle produces near-maximal work under most conditions in swimming fish. While muscle in the posterior region undergoes larger strain and thus produces more mass-specific power than muscle in the anterior region, when the longitudinal distribution of red muscle mass is considered, the anterior muscles appear to contribute approximately 40 % more total power. Mechanical work per length Cycle was maximal at a Cycle Frequency of 2–3 Hz, dropping to near zero at 15 Hz and by 20–50 % at 1 Hz. Mechanical power was maximal at a Cycle Frequency of 5 Hz, dropping to near zero at 15 Hz. These fish typically cruise with tail-beat frequencies of 2.8–5.2 Hz, frequencies at which power from cyclic contractions of deep red muscles was 75–100 % maximal. At any given Frequency over this range, power using stimulation conditions recorded from swimming fish averaged 93.4±1.65 % at ANT locations and 88.6±2.08 % at POST locations (means ± s.e.m., N =3–6) of the maximum using optimized conditions. When Cycle Frequency was held constant (4 Hz) and strain amplitude was increased, work and power increased similarly in muscles from both sample sites; work and power increased 2.5-fold when strain was elevated from ±2 to ±5.5 %, but increased by only approximately 12 % when strain was raised further from ±5.5 to ±8 %. Taken together, these data suggest that red muscle fibres along the entire body are used in a similar fashion to produce near-maximal mechanical power for propulsion during normal cruise swimming. Modelling suggests that the tail-beat Frequency at which power is maximal (5 Hz) is very close to that used at the predicted maximum aerobic swimming speed (5.8 Hz) in these fish.
George A Kowalchuk - One of the best experts on this subject based on the ideXlab platform.
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responses of antarctic soil microbial communities and associated functions to temperature and freeze thaw Cycle Frequency
Environmental Microbiology, 2008Co-Authors: Etienne Yergeau, George A KowalchukAbstract:Climatic changes will not only result in higher overall temperature, but also in greater variability in weather conditions. Antarctic soils are subjected to extremely variable conditions in the form of frequent freeze–thaw Cycles (FTCs), but the importance of alteration in FTC Frequency, compared with increases in average temperature and indirect vegetation-mediated effects on soil microorganisms, is still unknown. We therefore designed two complementary microcosm experiments using undisturbed soil cores from Signy Island (60°43'S, 45°38'W) in the maritime Antarctic. The experiments consisted of soil core incubations with or without the overlying vegetation at four different temperatures and six different FTC regimes. We assessed bacterial and fungal density and community structure, as well as the density of several key genes in microbial nutrient Cycles using a combination of RNA- and DNA-based molecular fingerprinting and quantitative PCR approaches in addition to enzymatic activity assays. Results showed that bacteria were more affected by warming than by changes in FTC Frequency. In contrast, fungal community structure and abundance were mostly influenced by FTC Frequency, as well as the presence of vegetation cover. The relative densities of several bacterial gene families involved in key steps of the N-Cycle were affected by FTCs, while warming had little or no effect. The FTCs and incubation temperature also strongly influenced laccase enzymatic activity in soil. In total, our results suggest that, in addition to climatic warming, increased climatic variability may also have a profound impact on Antarctic microbial communities. Although these effects are difficult to detect with assays of total bacterial community structure, they do become manifest in the analysis of key functional gene densities.
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responses of antarctic soil microbial communities and associated functions to temperature and freeze thaw Cycle Frequency
Environmental Microbiology, 2008Co-Authors: Etienne Yergeau, George A KowalchukAbstract:Climatic changes will not only result in higher overall temperature, but also in greater variability in weather conditions. Antarctic soils are subjected to extremely variable conditions in the form of frequent freeze-thaw Cycles (FTCs), but the importance of alteration in FTC Frequency, compared with increases in average temperature and indirect vegetation-mediated effects on soil microorganisms, is still unknown. We therefore designed two complementary microcosm experiments using undisturbed soil cores from Signy Island (60°43′S, 45°38′W) in the maritime Antarctic. The experiments consisted of soil core incubations with or without the overlying vegetation at four different temperatures and six different FTC regimes. We assessed bacterial and fungal density and community structure, as well as the density of several key genes in microbial nutrient Cycles using a combination of RNA- and DNA-based molecular fingerprinting and quantitative PCR approaches in addition to enzymatic activity assays. Results showed that bacteria were more affected by warming than by changes in FTC Frequency. In contrast, fungal community structure and abundance were mostly influenced by FTC Frequency, as well as the presence of vegetation cover. The relative densities of several bacterial gene families involved in key steps of the N-Cycle were affected by FTCs, while warming had little or no effect. The FTCs and incubation temperature also strongly influenced laccase enzymatic activity in soil. In total, our results suggest that, in addition to climatic warming, increased climatic variability may also have a profound impact on Antarctic microbial communities. Although these effects are difficult to detect with assays of total bacterial community structure, they do become manifest in the analysis of key functional gene densities. © 2008 The Authors.
Jeanine M Donley - One of the best experts on this subject based on the ideXlab platform.
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Effects of temperature on power output and contraction kinetics in the locomotor muscle of the regionally endothermic common thresher shark (Alopias vulpinus).
Fish physiology and biochemistry, 2012Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Douglas A Syme, Scott A. Aalbers, David G. Mcgillivray, Diego BernalAbstract:The common thresher shark (Alopias vulpinus) is a pelagic species with medially positioned red aerobic swimming musculature (RM) and regional RM endothermy. This study tested whether the contractile characteristics of the RM are functionally similar along the length of the body and assessed how the contractile properties of the common thresher shark compare with those of other sharks. Contractile properties of the RM were examined at 8, 16 and 24 °C from anterior and posterior axial positions (0.4 and 0.6 fork length, respectively) using the work loop technique. Experiments were performed to determine whether the contractile properties of the RM are similar along the body of the common thresher shark and to document the effects of temperature on muscle power. Axial differences in contractile properties of RM were found to be small or absent. Isometric twitch kinetics of RM were ~fivefold slower than those of white muscle, with RM twitch durations of about 1 s at 24 °C and exceeding 5 s at 8 °C, a Q10 of nearly 2.5. Power increased approximately tenfold with the 16 °C increase in temperature, while the Cycle Frequency for maximal power only increased from about 0.5–1.0 Hz over this temperature range. These data support the hypothesis that the RM is functionally similar along the body of the common thresher shark and corroborate previous findings from shark species both with and without medial RM. While twitch kinetics suggest the endothermic RM is not unusually temperature sensitive, measures of power suggest that the RM is not well suited to function at cool temperatures. The Cycle Frequency at which power is maximized appeared relatively insensitive to temperature in RM, which may reflect the relatively cooler temperature of the thresher RM compared to that observed in lamnid sharks as well as the relatively slow RM phenotype in these large fish.
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thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard shark and shortfin mako shark
The Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard shark Triakis semifasciata and endothermic shortfin mako shark Isurus oxyrinchus . The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25°C for Triakis and 15 to 28°C for Isurus at Cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6–0.65 L ) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in mako sharks at unphysiologically cool temperatures (<20°C). We found no significant differences in optimal stimulus duration, phase, net work or power output between anterior and posterior bundles in each species. With increasing Cycle Frequency the stimulus duration yielding maximum power decreased while optimal phase occurred earlier. The Cycle Frequency at which peak power was generated in leopard shark RM was only affected slightly by temperature, increasing from about 0.6 to 1.0 Hz between 15 and 25°C. In contrast, mako RM showed a much more dramatic temperature sensitivity, with the peak power Frequency rising from <0.25 to 2.25 Hz between 15 and 28°C. These data support the hypothesis that the contractile properties of RM are functionally similar along the body in both species. In addition, our data identify a significant difference in the effect of temperature on net work and power output between these two shark species; at 15°C muscle from the ectothermic leopard shark performs relatively well in comparison with mako, while at higher temperatures, which reflect those normally experienced by the mako, the optimal Cycle Frequency for power is nearly double that of the leopard shark, suggesting that the mako may be able to maintain greater aerobic swimming speeds.
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thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard shark and shortfin mako shark
The Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard shark Triakis semifasciata and endothermic shortfin mako shark Isurus oxyrinchus. The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25 degrees C for Triakis and 15 to 28 degrees C for Isurus at Cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6-0.65 L) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in mako sharks at unphysiologically cool temperatures (<20 degrees C). We found no significant differences in optimal stimulus duration, phase, net work or power output between anterior and posterior bundles in each species. With increasing Cycle Frequency the stimulus duration yielding maximum power decreased while optimal phase occurred earlier. The Cycle Frequency at which peak power was generated in leopard shark RM was only affected slightly by temperature, increasing from about 0.6 to 1.0 Hz between 15 and 25 degrees C. In contrast, mako RM showed a much more dramatic temperature sensitivity, with the peak power Frequency rising from <0.25 to 2.25 Hz between 15 and 28 degrees C. These data support the hypothesis that the contractile properties of RM are functionally similar along the body in both species. In addition, our data identify a significant difference in the effect of temperature on net work and power output between these two shark species; at 15 degrees C muscle from the ectothermic leopard shark performs relatively well in comparison with mako, while at higher temperatures, which reflect those normally experienced by the mako, the optimal Cycle Frequency for power is nearly double that of the leopard shark, suggesting that the mako may be able to maintain greater aerobic swimming speeds.
