Effect of ontogenetic increases in body size on burst swimming performance in tadpoles of the striped marsh frog, Limnodynastes peronii

The effect of ontogenetic increases in total length on burst swimming performance was investigated in tadpoles of the striped marsh frog (Limnodynastes peronii) over the total-length range of 1. 5-4 cm and Gosner developmental stages 25-38. The burst swimming performance of tadpoles at 10 degrees and 24 degrees C was determined by videotaping startle responses with a high-speed video camera at 200 Hz and analysing the sequences frame by frame. Maximum swimming velocity (Umax) and acceleration (Amax) increased with total length (L) at a rate that was proportionally greater than the increase in total length (i.e., positive allometry; exponents >1) and was described by the allometric equations Umax=0.061L1.34 and Amax=1.15L1.11 at 10 degrees C and Umax=0.114L1.34 and Amax=1.54L1. 11 at 24 degrees C. Stride length increased with a total-length exponent of approximately 1 but was unaffected by temperature. Tail-beat frequency was not affected by total length and increased from 7.8+/-0.2 Hz at 10 degrees C to 21.7+/-0.7 Hz at 24 degrees C. Developmental stage did not significantly influence the relationship between total length and Umax or Amax. Furthermore, temperature and the associated changes in water viscosity did not affect the relationship between total length and burst swimming performance. At their Umax, Reynolds numbers ranged from approximately 1,500 in the smaller tadpoles up to 50,000 for the larger animals at 24 degrees C. We suggest the positive allometry of Umax in larval L. peronii was due in part to the increases in tail width (TW) with total length (TW=-1.36L1.66), possibly reflecting the increasing importance of burst swimming performance to survival during larval development.     

Butanedione monoxime suppresses contraction and ATPase activity of rabbit skeletal muscle

The effects of 2,3-butanedione 2-monoxime (BDM) on mechanical responses of glycerinated fibers and the ATPase activity of heavy meromyosin (HMM) and myofibrils have been studied using rabbit skeletal muscle. The mechanical responses and the ATPase activity were measured in similar conditions (ionic strength 0.06-0.2 M, 0.4-4 mM MgATP, 0-20 mM BDM, 2-20 degrees C and pH 7.0). BDM reversibly reduced the isometric tension, shortening speed, and instantaneous stiffness of the fibers. BDM also inhibited myofibrillar and HMM ATPase activities. The inhibitory effect on the relative ATPase activity of HMM was not influenced by the addition of actin or troponin-tropomyosin-actin. High temperature and low ionic strength weakened BDM's suppression of contraction of the fibers and the ATPase activity of contracting myofibrils, but not of the HMM, acto-HMM and relaxed myofibrillar ATPase activity. The size of the initial phosphate burst at 20 degrees C was independent of the concentration of BDM. These results suggest that the suppression of contraction of muscle fibers is due mainly to direct action of BDM on the myosin molecules.     

Biochemical responses to temperature in the contractile protein complex of striped bass Morone saxatilis

The effects of acute and long-term changes in temperature upon catalytic and calcium regulatory function of red (slow oxidative) and white (fast glycolytic) muscle from striped bass (Morone saxatilis) were determined. Acclimation to 5 degrees C or 25 degrees C had no significant effect on catalytic function (ATPase activity) or regulatory sensitivity (Ca++-activation) of myofibrils from either muscle type. Substantial differences between red and white muscle were found in the intrinsic thermal sensitivity of maximally-activated Mg++-Ca++ myofibrillar ATPase. Arrhenius plots of myofibrillar ATPase from white muscle show one significant breakpoint at 29 degrees C, with activation energies (Ea) of 2.3 and 23.4 kcal mole-1 at temperatures above and below this transition, respectively. Arrhenius plots of myofibrillar ATPase from red muscle show two transitions occurring at 22 and 9 degrees C, with Ea of 7.6 kcal mole-1 above 22 degrees C and 18.3 kcal mole-1 between 9 and 22 degrees C. Activation energies for myofibrils from red muscle increase substantially to approximately 107.3 kcal mole-1 below the 9 degrees C breakpoint. Differences in the intrinsic thermal sensitivity of red and white muscle catalytic function are apparently due to interaction of actomyosins and calcium regulatory proteins which are specific to each muscle type. The results suggest that capacity for sustained swimming in striped bass, which is powered exclusively by red muscle, will be severely impaired at cold temperature unless compensations occur above the level of contractile proteins.     

Interacting effects of predation risk and resource level on escape speed of amphibian larvae along a latitudinal gradient

Fast‐growing genotypes living in time‐constrained environments are often more prone to predation, suggesting that growth‐predation risk trade‐offs are important factors maintaining variation in growth along climatic gradients. However, the mechanisms underlying how fast growth increases predation‐mediated mortality are not well understood. Here, we investigated if slow‐growing, low‐latitude individuals have faster escape swimming speed than fast‐growing high‐latitude individuals using common frog (Rana temporaria) tadpoles from eight populations collected along a 1500 km latitudinal gradient. We measured escape speed in terms of burst and endurance speeds in tadpoles raised in the laboratory at two food levels and in the presence and absence of a predator (Aeshna dragonfly larvae). We did not find any latitudinal trend in escape speed performance. In low food treatments, burst speed was higher in tadpoles reared with predators but did not differ between high‐food treatments. Endurance speed, on the contrary, was lower in high‐food tadpoles reared with predators and did not differ between treatments at low food levels. Tadpoles reared with predators showed inducible morphology (increased relative body size and tail depth), which had positive effects on speed endurance at low but not at high food levels. Burst speed was positively affected by tail length and tail muscle size in the absence of predators. Our results suggest that escape speed does not trade‐off with fast growth along the latitudinal gradient in R. temporaria tadpoles. Instead, escape speed is a plastic trait and strongly influenced by the interaction between resource level and predation risk.     

Both incubation temperature and posthatching temperature affect swimming performance and morphology of wood frog tadpoles (Rana sylvatica)

In many oviparous vertebrates, hatchling phenotypes are influenced by egg incubation temperature. Many of those phenotypic traits can also acclimate to long-term thermal conditions of juveniles and adults, yet the interactive effects of prehatching and posthatching temperatures on phenotypes have not been studied. To address such interaction, we incubated eggs of wood frogs (Rana sylvatica) at two temperatures and subsequently reared larvae at three temperatures in a fully factorial design. We measured body size, size-independent morphology, and burst swimming speed at one developmental stage. Body size was independent of egg temperature but decreased significantly with increasing larval temperature. Size-independent morphology depended in complex ways on both temperature treatments directly and on their interaction. Burst speed was not influenced directly by egg temperature but was influenced by larval temperature and by the interactions among egg temperature, larval temperature, and test temperature. Our results indicate pervasive effects of egg temperature even late in the larval period and show that prehatching and posthatching temperatures can interact to affect various phenotypic traits. Tadpoles may be able to alter the long-term effects of incubation temperature by choosing particular larval developmental temperatures. Thus, the importance of incubation temperature in oviparous vertebrates should be evaluated by considering the effects of posthatching temperatures.     

Stenotherms at sub-zero temperatures: thermal dependence of swimming performance in Antarctic fish

We examined the burst swimming performance of two Antarctic fishes, Trematomus bernacchii and T. centronotus, at five temperatures between -1 degrees C and 10 degrees C. As Antarctic fishes are considered one of the most cold specialised and stenothermal of all ectotherms, we predicted they would possess a narrow thermal performance breadth for burst swimming and a correlative decrease in performance at high temperatures. Burst swimming was assessed by videotaping swimming sequences with a 50-Hz video camera and analysing the sequences frame-by-frame to determine maximum velocity, the distance moved throughout the initial 200 ms, and the time taken to reach maximum velocity. In contrast to our prediction, we found both species possessed a wide thermal performance breadth for burst swimming. Although maximum swimming velocity for both T. bernacchii and T. centronotus was significantly highest at 6 degrees C, maximum velocity at all other test temperatures was less than 20% lower. Thus, it appears that specialisation to a highly stable and cold environment is not necessarily associated with a narrow thermal performance breadth for burst swimming in Antarctic fish. We also examined the ability of the Antarctic fish Pagothenia borchgrevinki to acclimate their burst-swimming performance to different temperatures. We exposed P. borchgrevinki to either -1 degrees C or 4 degrees C for 4 weeks and tested their burst-swimming performance at four temperatures between -1 degrees C and 10 degrees C. Burst-swimming performance of Pagothenia borchgrevinki was unaffected by exposure to either -1 degrees C or 4 degrees C for 4 weeks. Maximum swimming velocity of both acclimation groups was thermally independent over the total temperature range of 1 degrees C to 10 degrees C. Therefore, the loss of any capacity to restructure the phenotype and an inability to thermally acclimate swimming performance appears to be associated with inhabiting a highly stable thermal environment.     

Embryonic Developmental Temperatures Modulate Thermal Acclimation of Performance Curves in Tadpoles of the Frog Limnodynastes peronii

Performance curves of physiological rates are not fixed, and determining the extent to which thermal performance curves can change in response to environmental signals is essential to understand the effect of climate variability on populations. The aim of this study was to determine whether and how temperatures experienced during early embryonic development affect thermal performance curves of later life history stages in the frog Limnodynastes peronii. We tested the hypotheses that a) the embryonic environment affects mean trait values only; b) temperature at which performance of tadpoles is maximal shifts with egg incubation temperatures so that performance is maximised at the incubation temperatures, and c) incubation temperatures modulate the capacity for reversible acclimation in tadpoles. Growth rates were greater in warm (25°C) compared to cold (15°C) acclimated (6 weeks) tadpoles regardless of egg developmental temperatures (15°C or 25°C, representing seasonal means). The breadth of the performance curve of burst locomotor performance (measured at 10, 15, 20, 25, and 30°C, representing annual range) is greatest when egg developmental and acclimation temperatures coincide. The mode of the performance curves shifted with acclimation conditions and maximum performance was always at higher temperatures than acclimation conditions. Performance curves of glycolytic (lactate dehydrogenase activities) and mitochondrial (citrate synthase and cytochrome c oxidase) enzymes were modulated by interactions between egg incubation and acclimation temperatures. Lactate dehydrogenase activity paralleled patterns seen in burst locomotor performance, but oxygen consumption rates and mitochondrial enzyme activities did not mirror growth or locomotor performance. We show that embryonic developmental conditions can modulate performance curves of later life-history stages, thereby conferring flexibilty to respond to environmental conditions later in life.     

Thermal acclimation of locomotor performance in tadpoles and adults of the aquatic frog Xenopus laevis

Among amphibians, the ability to compensate for the effects of temperature on the locomotor system by thermal acclimation has only been reported in larvae of a single species of anuran. All other analyses have examined predominantly terrestrial adult life stages of amphibians and found no evidence of thermal acclimatory capacity. We examined the ability of both tadpoles and adults of the fully aquatic amphibian Xenopus laevis to acclimate their locomotor system to different temperatures. Tadpoles were acclimated to either 12 °C or 30 °C for 4 weeks and their burst swimming performance was assessed at four temperatures between 5 °C and 30 °C. Adult X. laevis were acclimated to either 10 °C or 25 °C for 6 weeks and their burst swimming performance and isolated muscle performance was determined at six temperatures between 5 °C and 30 °C. Maximum swimming performance of cold-acclimated X. laevis tadpoles was greater at cool temperatures and lower at the highest temperature in comparison with the warm-acclimated animals. At the test temperature of 12 °C, maximum swimming velocity of tadpoles acclimated to 12 °C was 38% higher than the 30 °C-acclimation group, while at 30 °C, maximum swimming velocity of the 30 °C-acclimation group was 41% faster than the 12 °C-acclimation group. Maximum swimming performance of adult X. laevis acclimated to 10 °C was also higher at the lower temperatures than the 25 °C acclimated animals, but there was no difference between the treatment groups at higher temperatures. When tested at 10 °C, maximum swimming velocity of the 10 °C-acclimation group was 67% faster than the 25 °C group. Isolated gastrocnemius muscle fibres from adult X. laevis acclimated to 10 °C produced higher relative tetanic tensions and decreased relaxation times at 10 °C in comparison with animals acclimated to 25 °C. This is only the second species of amphibian, and the first adult life stage, reported to have the capacity to thermally acclimate locomotor performance. Accepted: 28 October 1999     

Developmental stability and genetic architecture: a comparison within and across thermal regimes in tadpoles

We investigated homogeneity of growth and development as indices of developmental stability in sibling tadpoles from two sampling regions of the common frog, Rana temporaria. One region is characterized by relatively warm breeding ponds with a short activity season (`north'), and one by relatively cool breeding ponds and a long activity season (`south'). Tadpoles from the two regions were raised in three different temperatures selected to mimic the natural variation throughout the range. The results show that (1) north tadpoles respond with a relatively greater increase in growth with increased temperature than south tadpoles, (2) mean growth rate and its coefficient of variation were negatively correlated in the temperature regime in which a population was primarily under selection in the wild, whereas no such correlation was found at temperatures more seldom encountered in the natural populations, (3) phenotypic and genetic correlations between morphological traits within individuals were positive and were relatively higher in north than south tadpoles in the warm treatment, but higher for south tadpoles in the cold treatment and (4) across thermal environments, south tadpoles showed significant genetic correlations, whereas the correlations for north tadpoles were not significantly different from zero. South tadpoles showed only positive genetic correlations (n=30), whereas 14 of 30 correlation coefficients were negative in north tadpoles. In conclusion, developmental stability for growth and morphometry was higher at `optimal' conditions and decreased at the tail ends of the reaction norms within regions, with marked differences reflecting selection history between regions.     

The peptide PIN changes the timing of transitory burst activation of timer-ATPase TIME in accordance with diapause development in eggs of the silkworm, Bombyx mori

TIME is an ATPase that measures a time interval by exhibiting transitory burst activation in eggs of the silkworm, Bombyx mori L. PIN is a peptide that regulates the time measurement of TIME. To address the mode of action of PIN, interactions between TIME and PIN were investigated. First, TIME was mixed with PIN for various periods (days) at 25 degrees C. The longer TIME was mixed with PIN, the later the transitory burst activation of TIME ATPase activity occurred, while no such delay occurred at 5 degrees C. Second, the capacity of PIN to bind with TIME was measured at the two temperatures by fluorescence polarization. The binding interaction was much tighter (nearly 1000 times) at 25 degrees C than that at 4 degrees C. Because the log EC50 (in nM) at 4 degrees C was about 7, PIN must dissociate from TIME at low temperatures at the physiological concentration of TIME in eggs. Thus, TIME appears to be restructured into a time-measuring conformation by PIN at the high temperatures of summer, whereas the TIME-PIN complex would dissociate at the low temperatures of winter. This dissociation acts as the preliminary cue for the ATPase activity burst of TIME, which in turn causes the completion of diapause development and initiates new developmental programs.     

Thermal acclimation of interactions: differential responses to temperature change alter predator-prey relationship

Different species respond differently to environmental change so that species interactions cannot be predicted from single-species performance curves. We tested the hypothesis that interspecific difference in the capacity for thermal acclimation modulates predator-prey interactions. Acclimation of locomotor performance in a predator (Australian bass, Macquaria novemaculeata) was qualitatively different to that of its prey (eastern mosquitofish, Gambusia holbrooki). Warm (25°C) acclimated bass made more attacks than cold (15°C) acclimated fish regardless of acute test temperatures (10-30°C), and greater frequency of attacks was associated with increased prey capture success. However, the number of attacks declined at the highest test temperature (30°C). Interestingly, escape speeds of mosquitofish during predation trials were greater than burst speeds measured in a swimming arena, whereas attack speeds of bass were lower than burst speeds. As a result, escape speeds of mosquitofish were greater at warm temperatures (25°C and 30°C) than attack speeds of bass. The decline in the number of attacks and the increase in escape speed of prey means that predation pressure decreases at high temperatures. We show that differential thermal responses affect species interactions even at temperatures that are within thermal tolerance ranges. This thermal sensitivity of predator-prey interactions can be a mechanism by which global warming affects ecological communities.     

黑斑侧褶蛙蝌蚪断尾后的补偿生长和发育研究

动物在经历不利的生长条件或环境后往往出现补偿生长。研究了黑斑侧褶蛙(Pelophylax nigromaculatus)蝌蚪经历来自食蚊鱼(Gambusia affinis)捕食造成断尾损伤后的补偿生长模式、断尾损失对蝌蚪游泳能力以及变态时间与大小的影响。结果表明,经历捕食压力后,全尾组和1/3断尾组蝌蚪的体长显著大于1/2断尾组蝌蚪的体长,全尾组和1/3断尾组之间的蝌蚪体长差异不显著;第19天时,1/2断尾组蝌蚪经过补偿生长后体长显著大于全尾组蝌蚪,1/3断尾组与全尾组和1/2断尾组之间的蝌蚪体长差异均不显著;三个实验组之间蝌蚪尾长差异不显著;全尾组蝌蚪的疾游速显著大于1/2断尾组蝌蚪的疾游速,1/3断尾组蝌蚪的疾游速与全尾组和1/2断尾组之间差异不显著,表明严重断尾对蝌蚪疾游速产生了消极影响。三个实验组蝌蚪的变态时间和变态前后形态差异均不显著。黑斑侧褶蛙蝌蚪能够在变态前调整生长轨迹补偿早期捕食风险造成的生长损失,断尾损失并不影响变态时间与大小,断尾超过一半的蝌蚪经过补偿生长后仍要付出一定的运动代价。     

Thermoregulatory responses to low-intensity prolonged swimming in water at various temperatures and treadmill walking on land

The purpose of the present study was to examine the effect of water temperature on the human body during low-intensity prolonged swimming. Six male college swimmers participated in this study. The experiments consisted of breast stroke swimming for 120 minutes in 23 degrees C, 28 degrees C and 33 degrees C water at a constant speed of 0.4 m.sec-1 in a swimming flume. The same subjects walked on a treadmill at a rate of approximately 50% of maximal oxygen uptake (VO2max) at the same relative intensity as the three swimming trials. Rectal temperature (Tre) in 33 degrees C water was unchanged during swimming for 120 minutes. Tre during treadmill walking increased significantly compared to the three different swimming trials. Tre, mean skin temperature (Tsk) and mean body temperature (Tb) in 23 degrees C and 28 degrees C water decreased significantly more than in both the 33 degrees C water and walking on land. VO2 during swimming in 23 degrees C water increased more than during swimming in the 28 degrees C and 33 degrees C trials; however, there were no significant differences in VO2 between the 23 degrees C swimming trial and treadmill walking. Heart rate (HR) during treadmill walking on land increased significantly compared with HR during the three swimming trials. Plasma adrenaline concentration at the end of the treadmill walking was higher than that at the end of each of the three swimming trials. Noradrenaline concentrations at the end of swimming in the 23 degrees C water and treadmill walking were higher than those during the other two swimming trials. Blood lactate concentration during swimming in 23 degrees C water was higher than that during the other two swimming trials and walking on land. These results suggest that the balance of heat loss and heat production is maintained in the warm water temperature. Therefore, a relatively warm water temperature may be desirable when prolonged swimming or other water exercise is performed at low intensity.     

Hypergravity exposure affects ventral root activity in tadpoles (Xenopus laevis)

In tadpoles, it is possible to observe the rhythmical, burstlike activity of spinal motoneurons by extracellular recordings from the ventral roots. We examined the effects of hypergravity on tadpole locomotion by using a model of fictive swimming in paralysed larvae of Xenopus laevis. Hypergravity (3g) treatment lasted 10 or 11 days. After the 3g-exposure, the mean burst duration of the 3g-animals was significantly (p < or = 0.01) increased compared to the 1g-controls. Readaptation was observed for 8 days after the end of the 3g-period. Burst duration also increases with the age of the tadpoles. Therefore, we postulate that hypergravity has a reversible effect on motor development, probably caused by a neurotrophic effect of a tonic base activity of the vestibular nuclei.     

The effects of temperature and salinity on the swimming ability of whiteleg shrimp, Litopenaeus vannamei

Swimming endurance of whiteleg shrimp, Litopenaeus vannamei exposed to various temperatures (15, 20, and 25 degrees C) and salinities (15, 32, and 40 per thousand) was determined in a swimming channel against one of five flow velocities (5.41, 6.78, 8.21, 10.11, and 11.47 cm s(-1)) for up to 9000 s. No shrimp swam the full 9000 s throughout the experiment. The swimming endurance decreased as swimming speed was increased at any of the temperatures and salinities tested and was significantly affected by temperature and salinity (P<0.05). The power model (nu x t(b) = a) showed a better fit to the relationship between swimming endurance (t, in s) and swimming speed (nu, in cm s(-1)) at any of the temperatures and salinities tested. The swimming ability index (SAI), defined as SAI = integral(0)(9000) vdt x 10(-4) (cm), was found to be temperature- and salinity-dependent in L. vannamei. The optimum temperature and salinity and corresponding maximum SAI were Topt = 21.3 degrees C and SAI(max21.3) = 7.37 cm; Sopt = 27.6 per thousand and SAI(max27.6) = 7.47 cm, respectively. The range of temperatures and salinities within which SAI is >90% of the maximum was estimated between 17.6 and 24.9 degrees C and between 18.5 and 36.7 per thousand, respectively. The results suggest that the power model fits well to the observed endurance estimates and the SAI is a good index to quantitatively describe the overall swimming ability of L. vannamei. Furthermore, temperature and salinity can limit the swimming performance of L. vannamei.     

The effects of temperature and swimming speed on instantaneous fuel use and nitrogenous waste excretion of the Nile tilapia.

The effects of acclimation temperature (30 degrees, 20 degrees, and 15 degrees C) and swimming speed on the aerobic fuel use of the Nile tilapia (Oreochromis niloticus; 8-10 g, 8-9-cm fork length) were investigated using a respirometric approach. As acclimation temperature was decreased from 30 degrees C to 15 degrees C, resting oxygen consumption (Mo2) and carbon dioxide excretion (Mco2) decreased approximately twofold, while nitrogenous waste excretion (ammonia-N plus urea-N) decreased approximately fourfold. Instantaneous aerobic fuel usage was calculated from respiratory gas exchange. At 30 degrees C, resting Mo2 was fueled by 42% lipids, 27% carbohydrates, and 31% protein. At 15 degrees C, lipid use decreased to 21%, carbohydrate use increased greatly to 63%, and protein use decreased to 16%. These patterns at 30 degrees C and 15 degrees C in tilapia paralleled fuel use previously reported in rainbow trout acclimated to 15 degrees C and 5 degrees C, respectively. Temperature also had a pronounced effect on critical swimming speed (UCrit). Tilapia acclimated to 30 degrees C had a UCrit of 5.63+/-0. 06 body lengths/s (BL/s), while, at 20 degrees C, UCrit was significantly lower at 4.21+/-0.14 BL/s. Tilapia acclimated to 15 degrees C were unable or unwilling to swim. As tilapia swam at greater speeds, Mo2 increased exponentially; Mo2min and Mo2max were 5.8+/-0.6 and 21.2+/-1.5 micromol O2/g/h, respectively. Nitrogenous waste excretion increased to a lesser extent with swimming speed. At 30 degrees C, instantaneous protein use while swimming at 15 cm/s ( approximately 1.7 BL/s) was 23%, and at UCrit (5.6 BL/s), protein use dropped slightly to 17%. During a 48-h swim at 25 cm/s (2.7 BL/s, approximately 50% UCrit), Mo2 and urea excretion remained unchanged, while ammonia excretion more than doubled by 24 h and remained elevated 24 h later. These results revealed a shift to greater reliance on protein as an aerobic fuel during prolonged swimming.     

Hypergravity susceptibility of ventral root activity during fictive swimming in tadpoles (Xenopus laevis)

1. Fictive swimming is an experimental model to study early motor development. As vestibular activity also affects the development of spinal motor projections, the present study focused on the question whether in Xenopus laevis tadpoles, the rhythmic activity of spinal ventral roots (VR) during fictive swimming revealed age-dependent modifications after hypergravity exposure. In addition, developmental characteristics for various features of fictive swimming between stages 37/38 and 47 were determined. Parameters of interest were duration of fictive swimming episodes, burst duration, burst frequency (i.e., cycle length), and rostrocaudal delay. 2. Ventral root recordings were performed between developmental stage 37/38, which is directly after hatching and stage 47 when the hind limb buds appear. The location of recording electrodes extended from myotome 4 to 17. 3. Hypergravity exposure by 3 g-centrifugation lasted 9 to 11 days. It started when embryos had just terminated gastrulation (stage 11/19-group), when first rhythmical activity in the ventral roots appeared (stage 24/27-group), and immediately after hatching (stage 37/41-group). Ventral root recordings were taken for 8 days after termination of 3 g-exposure. 4. Between stage 37/38 (hatching) and stage 47 (hind limb bud stage) burst duration, cycle length and rostrocaudal delay recorded between the 10th and 14th postotic myotome increased while episode duration decreased significantly. In tadpoles between stage 37 and 43, the rostrocaudal delay in the proximal tail part was as long as in older tadpoles while in caudal tail parts, it was shorter. During this period of development, there was also an age-dependent progression of burst extension in the proximal tail area that could not be observed between the 10th and 14th myotome. 6. After termination of the 3 g-exposure, the mean burst duration of VR activity increased significantly (p < 0.01) when 3 g-exposure started shortly after gastrulation but not when it started thereafter. Other parameters for VR activity such as cycle length, rostrocaudal delay and episode duration were not affected by this level of hypergravity. 7. It is postulated that (i) functional separation of subunits responsible for intersegmental motor coordination starts shortly after hatching of young tadpoles; and that (ii) gravity exerts a trophic influence on the development of the vestibulospinal system during different periods of embryonic development leading to the formation of more rigid neuronal networks earlier in the spinal than in the ocular projections.     

Hormone response of diabetic patients to exercise at cool and warm temperatures

Both exercise and high ambient temperatures stimulate the secretion of counterregulatory hormones which can change glucose homeostasis. We studied whether in diabetic patients there are any differences in the hormonal response to exercise performed at cool or warm ambient temperatures. A study was performed on eight male insulin-dependent patients at rest and during exercise at +10 degrees C and +30 degrees C. Exercise consisted of three consecutive 15-min periods at 60% of maximal aerobic capacity. The concentrations of plasma lactate and counterregulatory hormones at rest were similar at warm and cool temperature, whereas prolactin concentration was higher (P less than 0.01) at +30 degrees C. Exercise resulted in an increase in noradrenaline, growth hormone and prolactin (P less than 0.01), prevented the diurnal decrease in cortisol, but had no effect on glucagon. Hormone responses to exercise were similar at +10 degrees C and at +30 degrees C, except for cortisol and noradrenaline which showed greater responses at warm than at cool temperatures. This may have been due to the higher relative work load at warm compared to cool temperatures as suggested by the higher heart rate and greater increase of lactate at +30 degrees C. These data indicate that within a range of ambient temperatures commonly occurring in sports, the response of counterregulatory hormones is largely independent of ambient temperature in insulin-dependent diabetic patients.     

Temperature influences swimming speed, growth and larval duration in coral reef fish larvae

The effects of temperature on growth, pelagic larval duration (PLD) and maximum swimming speed were compared in the tropical fish marine species Amphiprion melanopus, to determine how temperature change affects these three factors critical to survival in larvae. The effects of rearing temperature (25 and 28 °C) on the length of the larval period and growth were examined in conjunction with the effects of swimming temperature (reared at 25 °C, swum at 25 and 28 °C, reared at 28 °C, swum at 25 and 28 °C) on critical swimming speed (U-crit). Larvae reared at 25 °C had a 25% longer pelagic larval duration (PLD) than larvae reared at 28 °C, 12.3 (±0.3) days compared with 9 (±0.6) days at 25 °C. To offset this effect of reduced developmental rate, growth and U-crit were measured in larvae reared at 28 and 25 °C at the same absolute age (7 days after hatching (dah)) and same developmental age (7 dah at 28 °C cf. 11 dah at 25 °C), corresponding to the day before metamorphosis. Larvae reared at 25 °C were smaller than larvae reared at 28 °C at the same absolute age (7 dah at 25 °C cf. 7 dah at 28 °C), yet larger at similar developmental age (11 dah at 25 °C cf. 7 dah at 28 °C) when weight and standard length were compared. This stage-specific size increase did not result in better performance in larvae at the same developmental age, as there was no difference in U-crit in premetamorphic larvae reared at either temperature (7 dah at 28 °C c.f 11 dah at 25 °C). However, U-crit was considerably slower in 7-day-old larvae reared at 25 °C than larvae of the same absolute age (7 dah) reared at 28 °C. Swimming temperature controls demonstrated that a change in temperature immediately prior to swimming tests did not effect swimming performance for larvae reared at either temperature.A decreased in rearing temperature resulted in longer larval durations, reduced growth rates and slower swimming development in larvae. However, the magnitude of the response of each of these traits varied considerably. As such, larvae reared at the lower temperature were a larger size at metamorphosis but had poorer relative swimming capabilities. This study highlights the importance of measuring a range of ecologically relevant traits in developing larvae to properly characterise their relative condition and performance in response to environmental change.     

Voluntary dehydration and alliesthesia for water

The purpose of this experiment was to explore the complex relationship between fluid consumption and consumption factors (thirst, voluntary dehydration, water alliesthesia, palatability, work-rest cycle) during a simulated 14.5-km desert walk (treadmill, 1.34 m X s-1, 5% grade, 40 degrees C dry bulb/26 degrees C wet bulb, and wind speed of approximately 1.2 m X s-1). Twenty-nine subjects were tested (30 min X h-1, 6 h) on each of two nonconsecutive days. The subjects were randomly assigned to one of three groups: tap water (n = 8), iodine-treated tap water (n = 11), or iodine-treated flavored tap water (n = 10). The temperature of the water was 40 degrees C during one trial and 15 degrees C on the other. Mean sweat losses (6 h) varied between 1.4 kg (warm iodine-treated; 232 +/- 44 g X h-1) and 3.0 kg (cool iodine-treated flavored; 509 +/- 50 g X h-1). Warm drinks were consumed at a lower rate than cool drinks (negative and positive alliesthesia). This decreased consumption resulted in the highest percent body weight losses (2.8 and 3.2%). Cooling and flavoring effects on consumption were additive and increased the rate of intake by 120%. The apparent paradox between reduced consumption concomitant with severe dehydration and hyperthermia is attributed to negative alliesthesia for warm water rather than an apparent inadequacy of the thirst mechanism. The reluctance to drink warm iodine-treated water resulted in significant hyperthermia, dehydration, hypovolemia, and, in two cases, heat illness.