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T Garland

Publications and source records attributed to T Garland.

17 recordsLinked to original sources
PubMed1998

Glucocorticoid response to forced exercise in laboratory house mice (Mus domesticus).

We examined the time course and sex differences of the glucocorticoid response to forced, moderate-intensity treadmill exercise in outbred laboratory house mice. Mice (n = 64 total) were divided into eight groups, each of four males and four females, which were run on a motorized treadmill at 1.0 km/h for either 0, 2, 5, 10, 15, 25, 40, or 60 min. Serum samples were taken immediately after exercise and corticosterone (CORT) concentration was determined by radioimmunoassay. Resting CORT levels ranged between 11.6 and 29.5 ng/mL for both sexes. CORT levels increased with length of exercise and then exhibited a plateau by 25 min in females and by 40 min in males. Females displayed a significantly more rapid increase in serum CORT levels and attained higher maximal CORT levels than males. Females also had significantly larger adrenal glands, both in absolute terms and relative to body mass.

Adrenal Glands↗
PubMed1998

Artificial selection for increased wheel-running behavior in house mice.

Replicated within-family selection for increased voluntary wheel running in outbred house mice (Mus domesticus; Hsd:ICR strain) was applied with four high-selected and four control lines (10 families/line). Mice were housed individually with access to activity wheels for a period of 6 days, and selection was based on the mean number of revolutions run on days 5 and 6. Prior to selection, heritabilities of mean revolutions run per day (rev/day), average running velocity (rpm), and number of minutes during which any activity occurred (min/day) were estimated by midparent-offspring regression. Heritabilities were 0.18, 0.28, and 0.14, respectively; the estimate for min/day did not differ significantly from zero. Ten generations of selection for increased rev/day resulted in an average 75% increase in activity in the four selected lines, as compared with control lines. Realized heritability averaged 0.19 (range, 0.12-0.24 for the high-activity lines), or 0.28 when adjusted for within-family selection. Rev/day increased mainly through changes in rpm rather than min/day. These lines will be studied for correlated responses in exercise physiology capacities and will be made available to other researchers on request.

Analysis of Variance↗
PubMed1998

Effects of voluntary activity and genetic selection on aerobic capacity in house mice (Mus domesticus).

An animal model was developed to study effects on components of exercise physiology of both "nature" (10 generations of genetic selection for high voluntary activity on running wheels) and "nurture" (7-8 wk of access or no access to running wheels, beginning at weaning). At the end of the experiment, mice from both wheel-access groups were significantly lighter in body mass than mice from sedentary groups. Within the wheel-access group, a statistically significant, negative relationship existed between activity and final body mass. In measurements of maximum oxygen consumption during forced treadmill exercise (VO2max), mice with wheel access were significantly more cooperative than sedentary mice; however, trial quality was not a significant predictor of individual variation in VO2max. Nested two-way analysis of covariance demonstrated that both genetic selection history and access to wheels had significant positive effects on VO2max. A 12% difference in VO2max existed between wheel-access selected mice, which had the highest mass-corrected VO2max, and sedentary control mice, which had the lowest. The respiratory exchange ratio at VO2max was also significantly lower in the wheel-access group. Our results suggest the existence of a possible genetic correlation between voluntary activity levels (behavior) and aerobic capacity (physiology).

Aerobiosis↗
PubMed1995

Maximal sprint speeds and muscle fiber composition of wild and laboratory house mice.

We compared males from four groups of house mice (Mus domesticus), all bred and raised under common conditions in the laboratory: randombred Hsd:ICR; a wild population from Wisconsin; hybrids from lab dams; hybrids from wild dams. Wild mice were much faster sprinters (maximal forced sprint speeds over 1.0 m ranged from 2.38 to 3.34 m/s) than were lab mice (range = 0.89-1.68 m/s). Hybrids exhibited intermediate speeds (range = 1.54-2.70 m/s) and body masses, indicating largely additive inheritance. Type-specific mean muscle fiber cross-sectional areas of the gastrocnemius muscle did not differ significantly among groups. Percentage cross-sectional areas occupied by each of the three identified fiber types also did not differ significantly among groups, nor did they covary with body mass. For their body mass, however, lab mice had smaller gastrocnemius muscles than did wild and hybrid mice, which had muscles of similar size. Although we cannot rule out the possibility that smaller gastrocnemius muscles or slight differences in fiber composition account for the lower sprint speeds of the lab mice, we suggest that differences in unmeasured physiological, behavioral or motivational factors are probably the primary cause. This interpretation is supported by a lack of correlation between individual differences in sprint speed and either relative gastrocnemius muscle mass or muscle fiber type composition.

Animals↗
PubMed1994

Exercise physiology of wild and random-bred laboratory house mice and their reciprocal hybrids.

We conducted a "common garden" experiment to compare aspects of exercise physiology and voluntary wheel-running behavior in wild and random-bred (i.e., non-inbred) laboratory house mice and their reciprocal crosses. Analysis of covariance indicated that, after effects of body mass and other appropriate covariates (e.g., age at testing) were accounted for, wild (range 2.46-3.30 m/s, n = 12) and hybrid (range 1.69-3.30 m/s, n = 24) mice exhibited forced maximal sprint running speeds that averaged approximately 50% higher than those of random-bred laboratory mice (range 1.11-2.12 m/s, n = 19). Wild and hybrid mice also had significantly higher (+22%) mass-corrected maximal rates of oxygen consumption (VO2max) during forced exercise and greater (+12%) relative ventricle masses than lab mice. Wild and hybrid mice also showed statistically higher swimming endurance times relative to body mass than lab mice, although these differences were insignificant when body mass was not used as a covariate. No significant differences were found for relative gastrocnemius muscle mass, liver mass, hematocrit, or blood hemoglobin content. During a 7-day test on voluntary activity wheels, both wild and hybrid mice ran significantly more total revolutions (+101%), ran at higher average velocities when they were active (+69%), and exhibited higher maximum revolutions in any single 1-min period (+41% on the 7th day of testing), but the total number of active 1-min intervals did not differ significantly among groups. In general, the behavioral and/or whole organisms performance traits showed greater differences than the lower-level traits; thus, during the domestication of house mice, behavior may have evolved more rapidly than physiology.

Animals↗
PubMed1992

Individual variation in locomotor behavior and maximal oxygen consumption in mice.

Individual differences in open-field activity and emotionality (number of defecations and urinations), voluntary wheel running, voluntary and forced maximal sprint running speed on a photocell-timed racetrack, swimming endurance, and maximal oxygen consumption (VO2max) were studied in 35 random bred male ICR mice. With the exception of latency in the open field and voluntary speed on a racetrack, all measurements were significantly repeatable on two successive trial days. Maximal oxygen consumption (corrected for body size) was positively correlated with amount of wheel running during each day of a 7-day test, and the correlation became stronger throughout the testing period; however, none of the daily correlations reached statistical significance. The first factor from a principal components (PC) analysis showed positive loadings (component correlations) for all measures of speed in the open field, for both voluntary and forced maximal speeds on the racetrack, and for VO2max, but a negative loading for emotionality. Wheel running and VO2max loaded positively on PC 2. Only swimming endurance loaded strongly on PC 3; this trait was uncorrelated with any other measure of physiology or behavior. These results suggest that measures of both voluntary and forced locomotor speed, as well as amount of voluntary wheel running, may be related to aerobic physiological capacities in untrained mice.

Animals↗
PubMed1990

Quantitative genetics of maximal oxygen consumption in a garter snake.

Broad-sense heritabilities and genetic correlations of maximal oxygen consumption (VO2max), blood hemoglobin levels, and ventricle mass were estimated in a natural population of snakes. Traits were measured for six or fewer presumed full-sibling offspring from each of 45 wild-caught gravid garter snakes (Thamnophis sirtalis). VO2max was highly reproducible between replicate trial days (r = 0.88). In an attempt to reduce maternal effects, correlations of each character with body mass, snout-vent length, age at testing, litter size, dam mass, and dam snout-vent length were removed by computing residuals from multiple-regression equations. These residuals were used in subsequent genetic analyses. Approximate coefficients of variation of residuals were 16% for VO2max, 19% for hemoglobin level, and 13% for ventricle mass. Broad-sense heritabilities were highly significant for all characters [P less than 0.0001; VO2max heritability (h2) = 0.88; hemoglobin level h2 = 0.63; ventricle mass h2 = 0.41], suggesting that they could respond genetically to selection. Phenotypic correlations (rP) among residual characters were significant only between VO2max and ventricle mass (rP = +0.27). VO2max and ventricle mass exhibited a significant (broad-sense) genetic correlation of +0.64; this might facilitate the correlated evolution of these two traits in response to natural or artificial selection. Ventricle mass and hemoglobin level showed a significant environmental correlation of +0.43. Treadmill endurance crawling time (Evolution 42: 335-350, 1988) showed a weak but significantly positive rP with VO2max (rP = +0.17).

Aging↗
PubMed1989

Individual correlation of morphology, muscle mechanics, and locomotion in a salamander.

Measurements were made on locomotor performance (burst run and swim speed, run and swim endurance), morphology (body, tail, and hindlimb length, body mass), and skeletal muscle mechanics (isometric: twitch and tetanic tension, rates of force development and relaxation; isotonic: maximal velocity of shortening and power output) in a size range of individual salamanders (Ambystoma tigrinum nebulosum) at 10 and 20 degrees C. The size dependence of each factor was determined, and the interindividual correlations among factors were measured after removal of size effects. Locomotor performance is positively related to body size: larger animals are faster and have higher endurance. Isometric tensions (standardized for muscle cross-sectional area) and isotonic properties are mass independent; rates of isometric force development and relaxation are negatively related to body mass. Locomotor performance capacities are not intercorrelated among individuals. Isometric force and rates of force development are highly intercorrelated as are maximal shortening velocity and power output. Several statistical techniques failed to uncover correlations among sets of variables (performance, morphology, muscle mechanics): neither fast individuals nor individuals with high endurance necessarily have relatively fast muscles or long limbs or tails after the effects of body size have been removed.

Ambystoma↗
PubMed1987

Seasonal, sexual, and individual variation in endurance and activity metabolism in lizards.

Amphibolurus nuchalis were collected in central Australia during mid- (January) and late summer (March). Endurance time at 1 km/h on a motorized treadmill is greater in larger lizards, scaling as M0.65. Maximal O2 consumption (VO2max) scales as M0.96; standard metabolic rate (SMR) scales as M0.83. Factorial aerobic scope thus increases ontogenetically (9.4 at 1 g vs. 15 at 50 g). All organ masses scale allometrically; larger lizards have relatively smaller livers, but larger hearts and thigh muscles. Hematocrit and hemoglobin increase during early ontogeny, but are mass independent in adults. Maximal in vitro catalytic rates were determined for citrate synthase (CS) and pyruvate kinase (PK) in liver, heart, and thigh muscle and for lactate dehydrogenase (LDH) (lactate oxidation) in heart. All enzyme activities (expressed per g tissue) scale positively, except CS in heart. Females exhibit lower SMR and heart CS activity. March animals exhibit elevated endurance, VO2max, heart LDH, and thigh CS and PK activities. Individual variation in endurance correlates with individual differences in heart LDH and thigh CS and/or PK activities. Individual differences in VO2max are partly related to variation in hematocrit.

Animals↗
PubMed1987

Effects of endurance training and captivity on activity metabolism of lizards.

Two groups of Amphibolurus nuchalis, an Australian agamid lizard, were maintained in captivity for 8 wk. The "trained" group was given submaximal exercise at 1 km/h on a motorized treadmill, 30 min/day, 5 days/wk; the treadmill was inclined 10% for the last 5 wk. The "sedentary" group was not exercised. Endurance capacity did not change significantly in either group, but sprint speed decreased in trained lizards. The sedentary group exhibited significant decreases in maximal O2 consumption, standard metabolic rate, and heart mass, but an increase in liver mass. Trained lizards exhibited significant decreases in heart and thigh muscle masses, but significant increases in liver mass, hematocrit, liver pyruvate kinase, and heart citrate synthase activities. It is concluded that the adaptive response to endurance training, typical of mammals, does not generally occur in lizards. Moreover, levels of chronic activity that would elicit adaptive responses in mammals may be excessive for lizards and may induce pathological effects in joints and skeletal muscle. The ecological and evolutionary significance of these conclusions is discussed.

Analysis of Variance↗
PubMed1984

Physiological correlates of locomotory performance in a lizard: an allometric approach.

Three measures of locomotory performance and a series of variables thought to affect performance were measured in the iguanid lizard Ctenosaura similis. Burst speed is mass independent; however, endurance time at 1 km/h (EN-DUR) and maximal distance run (MAX DIS) scale as M0.3. Standard and maximal rates of O2 consumption (VO2max) scale as M0.9; VO2max averages 10-fold greater than standard metabolic rate (SMR). Three of ten enzyme activities measured exhibit significant scaling. After statistically removing the effects of body mass, multiple-regression analysis indicates that 1) 89% of the residual variation in ENDUR is correlated with variation among individuals in thigh muscle mass, VO2max, heart mass, and liver citrate synthase (CS) activity; 2) maximal CO2 consumption (VCO2max) and thigh pyruvate kinase activity statistically explain 64% of the variation in MAX DIS; 3) heart and liver masses together predict 35% of the variation in SMR; 4) thigh and liver CS activity, heart lactate dehydrogenase (LDH) activity, and hematocrit account for 67% of the variation in VO2max;5) 97% of the variation in VCO2max is statistically related to variation in liver CS activity, thigh and heart masses, and heart LDH activity.

Adenosine Triphosphatases↗
PubMedDate not supplied

Serum tumor necrosis factor associated with malaria in patients in the Solomon Islands.

There is now significant evidence that tumor necrosis factor (TNF) is involved in the pathogenesis of malaria. We have tested sera from patients presenting with a febrile illness admitted to hospital in Honiara, Solomon Islands, for the presence of TNF, interferon-gamma, and interleukin-1 (IL-1). This study differs from previous reports as the subjects were mainly adults from a semi-immune population living in an endemic area. The results from 2 different commercially-available assays for TNF were compared, and one was found to be superior to the other. Serum TNF concentrations correlated with malarial parasite density and the patients' temperatures, but not with interferon or IL-1. The results are discussed in the context of the immunopathology of this disease.

Adolescent↗