Biomedical subjects

Kathryn A Dickson

Publications and source records attributed to Kathryn A Dickson.

6 recordsLinked to original sources

PubMed2006

Mitochondrial proton leak rates in the slow, oxidative myotomal muscle and liver of the endothermic shortfin mako shark (Isurus oxyrinchus) and the ectothermic blue shark (Prionace glauca) and leopard shark (Triakis semifasciata).

Mitochondrial proton leak was assessed as a potential heat source in the slow, oxidative (red) locomotor muscle and liver of the shortfin mako shark (Isurus oxyrinchus), a regional endotherm that maintains the temperature of both tissues elevated above ambient seawater temperature. We hypothesized that basal proton leak rates in red muscle and liver mitochondria of the endothermic shortfin mako shark would be greater than those of the ectothermic blue shark (Prionace glauca) and leopard shark (Triakis semifasciata). Respiration rate and membrane potential in isolated mitochondria were measured simultaneously at 20 degrees C using a Clark-type oxygen electrode and a lipophilic probe (triphenylmethylphosphonium, TPMP(+)). Succinate-stimulated respiration was titrated with inhibitors of the electron transport chain, and the non-linear relationship between respiration rate and membrane potential was quantified. Mitochondrial densities of both tissues were measured by applying the point-contact method to electron micrographs so that proton leak activity of the entire tissue could be assessed. In all three shark species, proton leak occurred at a higher rate in red muscle mitochondria than in liver mitochondria. For each tissue, the proton leak curves of the three species overlapped and, at a membrane potential of 160 mV, mitochondrial proton leak rate (nmol H(+) min(-1) mg(-1) protein) did not differ significantly between the endothermic and ectothermic sharks. This finding indicates that red muscle and liver mitochondria of the shortfin mako shark are not specialized for thermogenesis by having a higher proton conductance. However, mako mitochondria did have higher succinate-stimulated respiration rates and membrane potentials than those of the two ectothermic sharks. This means that under in vivo conditions mitochondrial proton leak rates may be higher in the mako than in the ectothermic species, due to greater electron transport activity and a larger proton gradient driving proton leak. We also estimated each tissue's total proton leak by combining mitochondrial proton leak rates at 160 mV and tissue mitochondrial density data with published values of relative liver or red muscle mass for each of the three species. In red muscle, total proton leak was not elevated in the mako shark relative to the two ectothermic species. In the liver, total proton leak would be higher in the mako shark than in both ectothermic species, due to a lower proton conductance in the blue shark and a lower liver mitochondrial content in the leopard shark, and thus may contribute to endothermy.

Animals↗

PubMed2004

Tuna comparative physiology.

Thunniform swimming, the capacity to conserve metabolic heat in red muscle and other body regions (regional endothermy), an elevated metabolic rate and other physiological rate functions, and a frequency-modulated cardiac output distinguish tunas from most other fishes. These specializations support continuous, relatively fast swimming by tunas and minimize thermal barriers to habitat exploitation, permitting niche expansion into high latitudes and to ocean depths heretofore regarded as beyond their range.

Animals↗

PubMed2003

Swimming performance studies on the eastern Pacific bonito Sarda chiliensis, a close relative of the tunas (family Scombridae) II. Kinematics.

The swimming kinematics of the eastern Pacific bonito Sarda chiliensis at a range of sustained speeds were analyzed to test the hypothesis that the bonito's swimming mode differs from the thunniform locomotor mode of tunas. Eight bonito (fork length FL 47.5+/-2.1 cm, mass 1.25+/-0.15 kg) (mean +/- S.D.) swam at speeds of 50-130 cm s(-1) at 18+/-2 degrees C in the same temperature-controlled water tunnel that was used in previous studies of tunas. Kinematics variables, quantified from 60 Hz video recordings and analyzed using a computerized, two-dimensional motion analysis system, were compared with published data for similar sized tunas at comparable speeds. Bonito tailbeat frequency, tailbeat amplitude and stride length all increased significantly with speed. Neither yaw (6.0+/-0.6%FL) nor propulsive wavelength (120+/-65% fish total length) varied with speed, and there were no mass or body-length effects on the kinematics variables for the size range of bonitos used. Relative to similar sized yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas at similar speeds, the bonito has a lower tailbeat frequency, a higher yaw and a greater stride length. The lateral displacement and bending angle of each intervertebral joint during a complete tailbeat cycle were determined for the bonito at a swimming speed of 90 cm s(-1). The pattern of mean maximum lateral displacement (z(max)) and mean maximum bending angle (beta(max)) along the body in the bonito differed from that of both chub mackerel Scomber japonicus and kawakawa tuna Euthynnus affinis; z(max) was highest in the bonito. This study verifies that S. chiliensis is a carangiform swimmer and supports the hypothesis that the thunniform locomotor mode is a derived tuna characteristic associated with changes in this group's myotomal architecture. The finding that yaw and z(max) were greater in the bonito than in both mackerels and tunas suggests that swimming kinematics in the bonito is not intermediate between that of tunas and mackerels, as would be predicted on the basis of morphological characteristics.

Animals↗

PubMed2003

Morphological and enzymatic correlates of aerobic and burst performance in different populations of Trinidadian guppies Poecilia reticulata.

We examined the mechanistic basis for two whole-animal performance traits, aerobic capacity and burst speed, in six laboratory-reared Trinidadian guppy populations from different native drainages with contrasting levels of predation. Using within- and between-population variation, we tested whether variation in organs and organ systems (heart, gill and swimming motor mass) and the activities of several enzymes that support locomotion (citrate synthetase, lactate dehydrogenase and myofibrillar ATPase) are correlated with aerobic performance (maximum rates of oxygen consumption, (O(2)max)) or burst performance (maximum swim speed during escape responses). We also tested for associations between physiological traits and habitat type (different drainages and predation levels). Organ size and enzyme activities showed substantial size-independent variation, and both performance measures were strongly correlated to body size. After accounting for size effects, neither burst nor aerobic performance was strongly correlated to any organ size or enzymatic variable, or to each other. Two principal components (PCI, PC2) in both males and females accounted for most of the variance in the organ size and enzymatic variables. In both sexes, heart and gill mass tended to covary and were negatively associated with citrate synthetase and lactate dehydrogenase activity. In males (but not females), variation in aerobic performance was weakly but significantly correlated to variation in PC1, suggesting that heart and gill mass scale positively with (O(2)max). Neither of the component variables and no single morphological or enzymatic trait was correlated to burst speed in either sex. Evolutionary changes in important life history traits occur rapidly in guppy populations subjected to different predation intensities (high mortality in downstream sites inhabited by large predatory fish; low mortality in upstream sites lacking large predators). We found significant differences between stream drainages in all morphological variables and most enzymatic variables, but only the mass of the swimming motor and LDH activity were significantly affected by predation regime. Overall, our data show that microevolution has occurred in the physiological foundations of locomotor performance in guppies, but evolutionary changes in physiology do not closely correspond to the predation-induced changes in life history parameters.

Adenosine Triphosphatases↗

PubMed2002

Effects of temperature on sustained swimming performance and swimming kinematics of the chub mackerel Scomber japonicus.

The effects of a 6 degrees C difference in water temperature on maximum sustained swimming speed, swimming energetics and swimming kinematics were measured in the chub mackerel Scomber japonicus (Teleostei: Scombridae), a primarily coastal, pelagic predator that inhabits subtropical and temperate transition waters of the Atlantic, Pacific and Indian Oceans. New data for chub mackerel acclimated to 18 degrees C are compared with published data from our laboratory at 24 degrees C. Twelve individuals acclimated to each of two temperatures (15.6-26.3 cm fork length, FL, and 34-179 g at 18 degrees C; 14.0-24.7 cm FL and 26-156 g at 24 degrees C) swam at a range of speeds in a temperature-controlled Brett-type respirometer, at the respective acclimation temperature. At a given fish size, the maximum speed that S. japonicus was able to maintain for a 30-min period, while swimming steadily using slow, oxidative locomotor muscle (U(max,c)), was significantly greater at 24 than at 18 degrees C (52.5-97.5 cm s(-1) at 18 degrees C and 70-120 cm s(-1) at 24 degrees C). At a given speed and fish size, the rate of oxygen consumption (VO(2)) was significantly higher at 24 than at 18 degrees C because of a higher net cost of transport (1073-4617 J km(-1) kg(-1) at 18 degrees C and 2708-14895 J km(-1) kg(-1) at 24 degrees C). Standard metabolic rate, calculated by extrapolating the logO(2) versus swimming speed relationship to zero speed, did not vary significantly with temperature or fish mass (126.4+/-67.2 mg O(2) h(-1) kg(-1) at 18 degrees C and 143.2+/-80.3 mg O(2) h(-1) kg(-1) at 24 degrees C; means +/- S.D., N=12). Swimming kinematics was quantified from high-speed (120 Hz) video recordings analyzed with a computerized, two-dimensional motion-analysis system. At a given speed and fish size, there were no significant effects of temperature on tail-beat frequency, tail-beat amplitude or stride length, but propulsive wavelength increased significantly with temperature as a result of an increase in propulsive wave velocity. Thus, the main effects of temperature on chub mackerel swimming were increases in both U(max,c) and the net cost of swimming at 24 degrees C. Like other fishes, S. japonicus apparently must recruit more slow, oxidative muscle fibers to swim at a given sustainable speed at the lower temperature because of the reduced power output. Thus, the 24 degrees C mackerel reach a higher speed before they must recruit the fast, glycolytic fibers, thereby increasing U(max,c) at 24 degrees C. By quantifying in vivo the effects of temperature on the swimming performance of an ectothermic species that is closely related to the endothermic tunas, this study also provides evidence that maintaining the temperature of the slow, oxidative locomotor muscle at 6 degrees C or more above ambient water temperature in tunas should significantly increase sustainable swimming speeds, but also increase the energetic cost of swimming, unless cardiac output limits muscle performance.

Animals↗

PubMedDate not supplied

Evolution and consequences of endothermy in fishes.

Regional endothermy, the conservation of metabolic heat by vascular countercurrent heat exchangers to elevate the temperature of the slow-twitch locomotor muscle, eyes and brain, or viscera, has evolved independently among several fish lineages, including lamnid sharks, billfishes, and tunas. All are large, active, pelagic species with high energy demands that undertake long-distance migrations and move vertically within the water column, thereby encountering a range of water temperatures. After summarizing the occurrence of endothermy among fishes, the evidence for two hypothesized advantages of endothermy in fishes, thermal niche expansion and enhancement of aerobic swimming performance, is analyzed using phylogenetic comparisons between endothermic fishes and their ectothermic relatives. Thermal niche expansion is supported by mapping endothermic characters onto phylogenies and by combining information about the thermal niche of extant species, the fossil record, and paleoceanographic conditions during the time that endothermic fishes radiated. However, it is difficult to show that endothermy was required for niche expansion, and adaptations other than endothermy are necessary for repeated diving below the thermocline. Although the convergent evolution of the ability to elevate slow-twitch, oxidative locomotor muscle temperatures suggests a selective advantage for that trait, comparisons of tunas and their ectothermic sister species (mackerels and bonitos) provide no direct support of the hypothesis that endothermy results in increased aerobic swimming speeds, slow-oxidative muscle power, or energetic efficiency. Endothermy is associated with higher standard metabolic rates, which may result from high aerobic capacities required by these high-performance fishes to conduct many aerobic activities simultaneously. A high standard metabolic rate indicates that the benefits of endothermy may be offset by significant energetic costs.

Adaptation, Physiological↗