Effects of meal size,meal type,body temperature,and body size on the specific dynamic action of the marine toad,Bufo marinus

Specific dynamic action (SDA), the accumulated energy expended on all physiological processes associated with meal digestion, is strongly influenced by features of both the meal and the organism. We assessed the effects of meal size, meal type, body temperature, and body size on the postprandial metabolic response and calculated SDA of the marine toad, Bufo marinus. Peak postprandial rates of O(2) consumption (.V(O2)) and CO(2) production (.V(CO2)) and SDA increased with meal size (5%-20% of body mass). Postprandial metabolism was impacted by meal type; the digestion of hard-bodied superworms (Zophobas larva) and crickets was more costly than the digestion of soft-bodied earthworms and juvenile rats. An increase in body temperature (from 20 degrees to 35 degrees C) altered the postprandial metabolic profile, decreasing its duration and increasing its magnitude, but did not effect SDA, with the cost of meal digestion remaining constant across body temperatures. Allometric mass exponents were 0.69 for standard metabolic rate, 0.85 for peak postprandial .V(O2), and 1.02 for SDA; therefore, the factorial scope of peak postprandial .V(O2) increased with body mass. The mass of nutritive organs (stomach, liver, intestines, and kidneys) accounted for 38% and 20% of the variation in peak postprandial .V(O2) and SDA, respectively. Toads forced to exercise experienced 25-fold increases in .V(O2) much greater than the 5.5-fold increase experience during digestion. Controlling for meal size, meal type, and body temperature, the specific dynamic responses of B. marinus are similar to those of the congeneric Bufo alvarius, Bufo boreas, Bufo terrestris, and Bufo woodhouseii.     

Specific dynamic action of ambystomatid salamanders and the effects of meal size, meal type, and body temperature

The past decade has witnessed a dramatic increase in studies of amphibian and reptile specific dynamic action (SDA). These studies have demonstrated that SDA, the summed energy expended on meal digestion and assimilation, is affected significantly by meal size, meal type, and body size and to some extent by body temperature. While much of this attention has been directed at anuran and reptile SDA, we investigated the effects of meal size, meal type, and body temperature on the postprandial metabolic responses and the SDA of the tiger salamander (Ambystoma tigrinum tigrinum). We also compared the SDA responses among six species of Ambystoma salamanders representing the breadth of Ambystoma phylogeny. Postprandial peaks in VO(2) and VO(2), duration of elevated metabolism, and SDA of tiger salamanders increased with the size of cricket meals (2.5%-12.5% of body mass). For A. tigrinum, as for other ectotherms, a doubling of meal size results in an approximate doubling of SDA, a function of equal increases in peak VO(2) and duration. For nine meal types of equivalent size (5% of body mass), the digestion of hard-bodied prey (crickets, superworms, mealworms, beetles) generated larger SDA responses than the digestion of soft-bodied prey (redworms, beetle larvae). Body temperature affected the profile of postprandial metabolism, increasing the peak and shortening the duration of the profile as body temperature increased. SDA was equivalent among three body temperatures (20 degrees, 25 degrees, and 30 degrees C) but decreased significantly at 15 degrees C. Comparatively, the postprandial metabolic responses and SDA of Ambystoma jeffersonianum, Ambystoma maculatum, Ambystoma opacum, Ambystoma talpoideum, Ambystoma texanum, and the conspecific Ambystoma tigrinum mavortium digesting cricket meals that were 5% of their body mass were similar (independent of body mass) to those of A. t. tigrinum. Among the six species, standard metabolic rate, peak postprandial VO(2), and SDA scaled with body mass with mass exponents of 0.72, 0.78, and 1.05, respectively.     

Effects of temperature on the specific dynamic action of the southern catfish, Silurus meridionalis

Specific dynamic action (SDA), the energy expended on all physiological processes that is associated with meal digestion and assimilation, is strongly affected by temperature. We assessed the effects of temperature on the postprandial metabolic response and calculated SDA of the southern catfish, Silurus meridionalis. The fish was fed with experimental diets at a meal size of 4% body mass, and by using an 8-chamber, continuous-flow respirometer the oxygen consumption rate was determined at a 2 h interval until the postprandial oxygen consumption rate returning to the preprandial level, at four different temperatures. The energy expended on SDA (SDA(E)) were 2.71, 3.07, 3.16, and 3.62 kJ, the SDA(coefficients) (energy expended on SDA quantified as a percentage of the digestible energy content of the meal) were 7.70, 9.44, 10.36, and 11.12%, and the peak metabolic rates (R(peak)) of SDA were 3.48, 4.31, 5.96, and 7.30 mg O2 h(-1), at 17.5, 22.5, 27.5, and 32.5 degrees C respectively. The relationships between those parameters and temperature were: SDA(E)=1.74+0.0559T (n=26, r(2)=0.676), SDA(coefficient)=4.10+0.223T (n=26, r(2)=0.726), and R(peak)=-1.34+0.264T (n=26, r(2)=0.896). The SDA durations showed a slow-fast-slow tendency of decrease with increasing temperature, and were 88.00, 85.71, 67.71, and 66.50 h at 17.5, 22.5, 27.5 and 32.5 degrees C respectively. Two separate peaks appeared during the SDA response at 17.5 degrees C, and it might be due to a rapid startup of the mechanical process with a lag of the biochemical process, which suggested that the peaks of "mechanical component" and "biochemical component" of SDA might be separated when temperature was low enough.     

Effects of temperature on the specific dynamic action of the southern catfish, Silurus meridionalis.

Specific dynamic action (SDA), the energy expended on all physiological processes that is associated with meal digestion and assimilation, is strongly affected by temperature. We assessed the effects of temperature on the postprandial metabolic response and calculated SDA of the southern catfish, Silurus meridionalis. The fish was fed with experimental diets at a meal size of 4% body mass, and by using an 8-chamber, continuous-flow respirometer the oxygen consumption rate was determined at a 2 h interval until the postprandial oxygen consumption rate returning to the preprandial level, at four different temperatures. The energy expended on SDA (SDA(E)) were 2.71, 3.07, 3.16, and 3.62 kJ, the SDA(coefficients) (energy expended on SDA quantified as a percentage of the digestible energy content of the meal) were 7.70, 9.44, 10.36, and 11.12%, and the peak metabolic rates (R(peak)) of SDA were 3.48, 4.31, 5.96, and 7.30 mg O2 h(-1), at 17.5, 22.5, 27.5, and 32.5 degrees C respectively. The relationships between those parameters and temperature were: SDA(E)=1.74+0.0559T (n=26, r(2)=0.676), SDA(coefficient)=4.10+0.223T (n=26, r(2)=0.726), and R(peak)=-1.34+0.264T (n=26, r(2)=0.896). The SDA durations showed a slow-fast-slow tendency of decrease with increasing temperature, and were 88.00, 85.71, 67.71, and 66.50 h at 17.5, 22.5, 27.5 and 32.5 degrees C respectively. Two separate peaks appeared during the SDA response at 17.5 degrees C, and it might be due to a rapid startup of the mechanical process with a lag of the biochemical process, which suggested that the peaks of "mechanical component" and "biochemical component" of SDA might be separated when temperature was low enough.     

Effects of body mass, meal size, fast length, and temperature on specific dynamic action in the timber rattlesnake (Crotalus horridus)

Detailed analysis of animal energy budgets requires information on the cost of digestion (specific dynamic action [SDA]), which can represent a significant proportion of ingested energy (up to 30% in infrequent feeders). We studied the effects of snake mass, temperature (25 degrees and 30 degrees C), fasting time (1 and 5 mo), and prey size (10%-50% of snake mass) on SDA in 26 timber rattlesnakes (Crotalus horridus). We used flow-through respirometry to measure hourly CO(2) production rates (VCO2) for 1 d before and up to 17 d after feeding. Crotalus horridus, like previously studied viperids and boids, show large and ecologically relevant increases in metabolism due to feeding. Depending on treatment and individual, VCO2 increased to 2.8-11.8 times the resting metabolic rate within 12-45 h postfeeding and decreased to baseline within 4.3-15.4 d. Significant effects of snake mass, meal mass, and fast length were detected. Increased temperature decreased the time required to complete the process but had little effect on total energy expended on SDA. Energy expended on SDA increased with increasing fast length, snake mass, and prey mass. Considering all of our data, we found that a simple allometric relationship explained 96.7% of the variation in total CO(2) production during SDA. Calculations suggest that energy devoted to SDA may approach 20% of the total annual energy budget of snakes in nature. Discrepancies between our data and some previous studies draw attention to the fact that the measurement, expression, and analysis of SDA may be sensitive to several methodological and statistical assumptions.     

Effect of meal size on postprandial metabolic response in southern catfish (Silurus meridionalis)

Effect of relative meal size (0.6-24%) on specific dynamic action (SDA) was assessed in southern catfish juveniles (48.2+/-3.2 g) at 27.5 degrees C. Cutlets of freshly killed loach species were used as test diet. Energy expended during SDA was linearly correlated with relative meal size (r=0.949, p<0.001, N=47). There was no significant difference in SDA coefficient (energy expended on SDA quantified as a percentage of the energy content of the meal) among different relative meal size groups. Factorial metabolic scope increased from 1.47 to 4.08 when the relative meal size increased from 0.6% to 24%. The peak V O2 increased with meal size, but levelled when relative meal size gradually increased to the maximum. SDA duration showed a S-type (slow-fast-slow) increase course with increased meal size. The results of this study suggest that the high postprandial factorial metabolic scope and a trapezoid SDA curve might be the adaptation strategy of warm water sit-and-wait fish under the natural selection of evolution related to long-term food resources.     

The influence of circadian rhythms on pre- and post-prandial metabolism in the snake Lamprophis fuliginosus

Measuring standard metabolic rate (SMR) and specific dynamic action (SDA) has yielded insight into patterns of energy expenditure in snakes, but less emphasis has been placed on identifying metabolic variation and associated energy cost of circadian rhythms. To estimate SMR, SDA, and identify metabolic variation associated with circadian cycles in nocturnally active African house snakes (Lamprophis fuliginosus), we measured oxygen consumption rates (VO2) at frequent intervals before and during digestion of meals equaling 10%, 20% and 30% of their body mass. Circadian rhythms in metabolism were perceptible in the VO2 data during fasting and after the initial stages of digestion. We estimated SMR of L. fuliginosus (mean mass=16.7+/-0.3 g) to be 0.68+/-0.02 (+/-SEM) mL O2/h at 25 degrees C. Twenty-four hours after eating, VO2 peaked at 3.2-5.3 times SMR. During digestion of meals equaling 10-30% of their body mass, the volume of oxygen consumed ranged from 109 to 119 mL O2 for SMR, whereas extra oxygen consumed for digestion and assimilation ranged from 68 to 256 mL O2 (equivalent to 14.5-17.0% of ingested energy). The oxygen consumed due to the rise in metabolism during the active phase of the daily cycle ranged from 55 to 66 mL O2 during digestion. Peak VO2, digestive scope, and SDA increased with increasing meal size. Comparisons of our estimates to estimates derived from methods used in previous investigations resulted in wide variance of metabolic variables (up to 39%), likely due to the influence of circadian rhythms and activity on the selection of baseline metabolism. We suggest frequent VO2 measurements over multiple days, coupled with mathematical methods that reduce the influence of undesired sources of VO2 variation (e.g., activity, circadian cycles) are needed to reliably assess SMR and SDA in animals exhibiting strong circadian cycles.     

Effects of meal size,meal type,and body temperature on the specific dynamic action of anurans

Specific dynamic action (SDA), the increase in metabolism stemming from meal digestion and assimilation, varies as a function of meal size, meal type, and body temperature. To test predictions of these three determinants of SDA, we quantified and compared the SDA responses of nine species of anurans, Bombina orientalis, Bufo cognatus, Ceratophrys ornata, Dyscophus antongilli, Hyla cinerea, Kassina maculata, Kassina senegalensis, Pyxicephalus adspersus, and Rana catesbeiana subjected to meal size, meal type, and body temperature treatments. Over a three to seven-fold increase in meal size, anurans experienced predicted increases in postprandial rates of oxygen consumption the duration of elevated and SDA. Meal type had a significant influence on the SDA response, as the digestion and assimilation of hard-bodied, chitinous crickets, mealworms, and superworms required 76% more energy than the digestion and assimilation of soft-bodied earthworms, waxworms, and neonate rodents. Body temperature largely effected the shape of the postprandial metabolic profile; peak increased and the duration of the response decreased with an increase in body temperature. Variation in body temperature did not significantly alter SDA for four species, whereas both H. cinerea and R. catesbeiana experienced significant increases in SDA with body temperature. For 13 or 15 species of anurans ranging in mass from 2.4 to 270 g, SMR, postprandial peak and SDA scaled with body mass (log–log) with mass exponents of 0.79, 0.93, and 1.05, respectively.     

Protein synthesis and specific dynamic action in crustaceans: effects of temperature

Temperature influences the specific dynamic action (SDA), or rise in oxygen uptake rate after feeding, in eurythermal and stenothermal crustaceans by changing the timing and the magnitude of the response. Intra-specific studies on the eurythermal crab, Carcinus maenas, show that a reduction in acclimation temperature is associated with a decrease in SDA magnitude, resulting from an increase in SDA duration but a decrease in peak factorial scope (the factorial rise in peak SDA over prefeeding values). Inter-specific feeding studies on stenothermal polar isopods revealed marked differences in SDA response between the Antarctic species, Glyptonotus antarcticus and the Arctic species, Saduria entomon. Compared to S. entomon held at 4 and 13 degrees C, the SDA response in G. antarcticus held at 1 degrees C was characterised by a lower absolute oxygen uptake rate at peak SDA and an extended SDA duration. At peak SDA, whole animal rates of protein synthesis increased in proportion to the postprandial increase in oxygen uptake rate in the Antarctic and the Arctic species. Rates of oxygen uptake plotted against whole animal rates of protein synthesis gave similar relationships in both isopod species, indicating similar costs of protein synthesis after a meal, despite their differences in SDA response and thermal habitat.     

The effect of meal composition on specific dynamic action in burmese pythons (Python molurus)

We quantified the specific dynamic action (SDA) resulting from the ingestion of various meal types in Burmese pythons (Python molurus) at 30 degrees C. Each snake was fed a series of experimental meals consisting of amino acid mixtures, simple proteins, simple or complex carbohydrates, or lipids as well as meals of whole animal tissue (chicken breast, beef suet, and mouse). Rates of oxygen consumption were measured for approximately 4 d after feeding, and the increment above standard metabolic rate was determined and compared to energy content of the meals. While food type (protein, carbohydrate, and lipid) had a general influence, SDA was highly dependent on meal composition (i.e., amino acid composition and carbohydrate structure). For chicken breast and simple carbohydrates, the SDA coefficient was approximately one-third the energetic content of the meal. Lard, suet, cellulose, and starch were not digested and did not produce measurable SDA. We conclude that the cost of de novo protein synthesis is an important component of SDA after ingestion of protein meals because (1) simple proteins, such as gelatin and collagen, did not stimulate levels of SDA attained after consumption of complete protein, (2) incomplete mixtures of amino acids failed to elicit the SDA of a complete mixture, and (3) the inhibition of de novo protein synthesis with the drug cycloheximide caused a more than 70% decrease in SDA. Stomach distension and mechanical digestion of intact prey did not cause measurable SDA.     

Specific dynamic action: a review of the postprandial metabolic response

For more than 200 years, the metabolic response that accompanies meal digestion has been characterized, theorized, and experimentally studied. Historically labeled “specific dynamic action” or “SDA”, this physiological phenomenon represents the energy expended on all activities of the body incidental to the ingestion, digestion, absorption, and assimilation of a meal. Specific dynamic action or a component of postprandial metabolism has been quantified for more than 250 invertebrate and vertebrate species. Characteristic among all of these species is a rapid postprandial increase in metabolic rate that upon peaking returns more slowly to prefeeding levels. The average maximum increase in metabolic rate stemming from digestion ranges from a modest 25% for humans to 136% for fishes, and to an impressive 687% for snakes. The type, size, composition, and temperature of the meal, as well as body size, body composition, and several environmental factors (e.g., ambient temperature and gas concentration) can each significantly impact the magnitude and duration of the SDA response. Meals that are large, intact or possess a tough exoskeleton require more digestive effort and thus generate a larger SDA than small, fragmented, or soft-bodied meals. Differences in the individual effort of preabsorptive (e.g., swallowing, gastric breakdown, and intestinal transport) and postabsorptive (e.g., catabolism and synthesis) events underlie much of the variation in SDA. Specific dynamic action is an integral part of an organism’s energy budget, exemplified by accounting for 19–43% of the daily energy expenditure of free-ranging snakes. There are innumerable opportunities for research in SDA including coverage of unexplored taxa, investigating the underlying sources, determinants, and the central control of postprandial metabolism, and examining the integration of SDA across other physiological systems.     

Specific dynamic action in the shore crab,Carcinus maenas (L.), in relation to acclimation temperature and to the onset of the emersion response

The rate of oxygen uptake (MO(2)) of shore crabs following a period of fasting varied directly with acclimation temperature, with a Q(10) of 2.96 between 7 degrees and 15 degrees C and a Q(10) of 2.11 between 15 degrees and 22 degrees C. The factorial rise in MO(2) following a meal (specific dynamic action [SDA]) ranged between 1.9 and 3.1 and varied with temperature, being highest at 15 degrees C and significantly lower at both 7 degrees and 22 degrees C, despite similar ration sizes in all groups. At 7 degrees C, the SDA coefficient and magnitude were significantly lower than at 15 degrees C, possibly due in part to the inhibition of protein synthesis. Both the time to peak and the duration of the SDA response were inversely related to temperature. SDA coefficients were inversely related to the amount of food consumed. The critical oxygen tension of inspired water (P(I)O(2)), which evoked the emersion response in fasted animals, increased with temperature and further increased at each temperature when the animals were fed. Thus, the threshold P(I)O(2) evoking the emersion response is directly related to relative metabolic oxygen demand in Carcinus.     

Oxygen consumption and the energetics of island-dwelling Florida cottonmouth snakes

We measured oxygen consumption (Vo(2)) to estimate standard metabolic rates (SMR) in cottonmouth snakes (Agkistrodon piscivorus conanti) from Seahorse Key and the adjacent peninsula of northern Florida. The island population is unusual because adult snakes feed on fish that are dropped by colonial nesting birds, and food resources are temporally limited relative to that of mainland populations. We found no differences in SMR between island and mainland snakes at any of four experimental temperatures (15 degrees -30 degrees C), suggesting that any adjustments to energy limitations involve other aspects of physiology or behavior. As with other viperid species, the SMR of cottonmouths is about one-half of that expected from interspecific allometric regressions previously reported for snakes generally. Allometric mass exponents of SMR averaged 0.76 and were not affected by temperature. We found that Vo(2) increased with temperature (Q(10) = 2.4-2.8) and was elevated 29% during scotophase compared with photophase. Neonates exhibited elevated Vo(2)compared with older juveniles of similar size, apparently due to assimilation of yolk that is present in the neonatal gut. In adult snakes, specific dynamic action (SDA) following feeding resulted in four- to eightfold increases in Vo(2), with magnitude and duration related positively to relative meal size. The total energy devoted to SDA increased with meal size and averaged 32.8%+/-4.4% of total ingested energy. We estimate that a nonreproductive 500-g adult cottonmouth at Seahorse Key uses 3,656 kJ of assimilated energy annually for maintenance and activity, which requires ingestion of approximately 1 kg of fish.     

The effects of meal size on postprandial metabolic response and post-exercise metabolic recovery process in juvenile black carp (Mylopharyngodon piceus)

The effects of meal size on the postprandial metabolic response and of digestion on the post-exercise metabolic recovery process were investigated in juvenile black carp (Mylopharyngodon piceus) . Experimental fish were forcedly fed with compound feed (meal sizes: 0.5%, 1% and 2% body weight). Then, the postprandial oxygen consumption rate and excess post-exercise oxygen consumption (EPOC) of the experimental fish were measured. Both the duration and the peak of oxygen consumption rate (PMR) increased with increasing meal size. The peak post-exercise metabolic rate of digesting fish were significantly higher, whereas EPOC magnitude and its duration were significantly smaller or (shorter) than those in the fasting fish. It is suggested that (1) this fish fulfills the increased energy demand during the digestive process by increasing PMR and by prolonging SDA duration with increasing meal size and (2) digesting fish might decrease their anaerobic exhaustive activity but increase the post-exercise recovery capacity.     

Effect of meal size on the specific dynamic action of the juvenile snakehead (Channa argus)

The effect of meal size on the specific dynamic action (SDA) of the juvenile snakehead (Channa argus) was assessed at 25 °C. The fish were fed with test diets at meal sizes of 0.5, 1, 2, 3, 4, and 5% body mass and the postprandial oxygen consumption rate was determined at 1-h intervals until it returned to the pre-prandial level. The peak metabolic rate increased from 237.4 to 283.2 mg O₂ kg^− 1 h^− 1 as the relative meal size increased from 0.5% to 3% and leveled off at 4% and 5%. Factorial metabolic scope increased from 1.53 to 1.99 and SDA duration increased from 11.7 to 32.3 h as the relative meal size increased from 0.5% to 5%. The relationship between SDA duration (D) and relative meal size (M) was described as: D = 4.28 M + 10.62 (r² = 0.752, P < 0.05, n = 50). The energy expended on SDA increased while the SDA coefficient decreased with increasing meal size. The results of the present study suggest that the snakehead may adopt different feeding strategies when taking in different amounts of food.     

Effects of body lipid content on the resting metabolic rate and postprandial metabolic response in the southern catfish Silurus meridionalis

We assessed the effects of body lipid content on the resting metabolic rate and specific dynamic action (SDA) of the southern catfish Silurus meridionalis. Obese and lean fish were obtained by feeding the fish with two different feeds at 27.5 °C for 4 weeks prior to the experiment. The fish were fed with experimental diets with a meal size of 4% by body mass. A continuous-flow respirometer was used to determine the oxygen consumption rate at 2-h intervals until the postprandial oxygen consumption rate had returned to the preprandial level. The body lipid content of the obese fish was significantly greater than that of the lean fish. The metabolic parameters evaluated (resting metabolic rate, peak metabolic rate (R_peak), factorial ratio, time to peak, duration, energy expended on SDA (SDA_E), or SDA coefficient) were not significantly affected by body fat content in terms of the whole-body or mass-specific values. Increased body fat content did not decrease the resting metabolic rate in the southern catfish, which might be due to the higher levels of highly unsaturated fatty acids in these fish. The results also suggest that the body composition does not appear to affect the SDA response.     

Effect of meal size on postprandial metabolic response in Chinese catfish (Silurus asotus Linnaeus)

The effect of relative meal size (0.5–24% body mass) on specific dynamic action (SDA) was assessed in Chinese catfish (Silurus asotus Linnaeus) (30.90±1.30 g) at 25.0°C; the cutlets of freshly killed loach without viscera, head and tail were used as a test meal. There was no significant difference in either SDA duration or peak oxygen consumption (VO₂) among low meal size ranges. But both increased linearly as meal size increased from 2 to 24% without reaching a plateau. Factorial metabolic scope was 5.92 in fish fed with 24% body mass, the highest documented feeding metabolic scope value in fish till now. The Peak VO₂ of satiated meal size groups (175.85±10.55 mg O₂ h⁻¹) was above 80% of maximum metabolic rate during locomotion recovery process (215.48±7.07 mg O₂ h⁻¹). The relationship between energy expended on SDA (E) and energy ingested (I) was described as: E=0.0000432I ²+0.140I+2.12. The lowest value of SDA coefficient appeared at 2% body mass group.     

Physiological response to feeding in little penguins

Specific dynamic action (SDA), the increase in metabolic rate above resting levels that accompanies the processes of digestion and assimilation of food, can form a substantial part of the daily energy budget of free-ranging animals. We measured heart rate (fH) and rate of oxygen consumption (VO2) in 12 little penguins while they digested a meal of sardines in order to determine whether they show specific dynamic action. In contrast to some studies of other penguin species, little penguins showed a substantial SDA, the magnitude of which was proportional to the size of the meal. The energy utilized in SDA was equivalent to 13.4% of the available energy content of the fish. Furthermore, animals such as penguins that forage in a cold environment will probably expend further energy in heating their food to body temperature to facilitate efficient digestion. It is estimated that this additional energy expenditure was equivalent to 1.6%-2.3% of the available energy content of the fish, depending on the time of year and therefore the temperature of the water. Changes in fH during digestion were qualitatively similar to those in VO2, implying that there were no substantial circulatory adjustments during digestion and that the relationship between fH and VO2 in penguins is unaffected by digestive state.     

The effects of acute and developmental temperature on burst swimming speed and myofibrillar ATPase activity in tadpoles of the Pacific tree frog, Hyla regilla

The effects of acute and developmental temperature on maximum burst swimming speed, body size, and myofibrillar ATPase activity were assessed in tadpoles of the Pacific tree frog, Hyla regilla. Tadpoles from field-collected egg masses were reared in the laboratory at 15 degrees (cool) and 25 degrees C (warm). Body size, maximum burst swimming speed from 5 degrees to 35 degrees C, and tail myofibrillar ATPase activity at 15 degrees and 25 degrees C were measured at a single developmental stage. Burst speed of both groups of tadpoles was strongly affected by test temperature (P<0. 001). Performance maxima spanned test temperatures of 15 degrees -25 degrees C for the cool group and 15 degrees -30 degrees C for the warm group. Burst speed also depended on developmental temperature (P<0.001), even after accounting for variation in body size. At most test temperatures, the cool-reared tadpoles swam faster than the warm-reared tadpoles. Myofibrillar ATPase activity was affected by test temperature (P<0.001). Like swimming speed, enzyme activity was greater in the cool-reared tadpoles than in the warm-reared tadpoles, a difference that was significant when assayed at 15 degrees C (P<0. 01). These results suggest a mechanism for developmental temperature effects on locomotor performance observed in other taxa.     

Plasticity of growth rate and metabolism in Daphnia magna populations from different thermal habitats

The aim of this study was to evaluate the effect of temperature on growth and aerobic metabolism in clones of Daphnia magna from different thermal regimes. Growth rate (increment in size), somatic juvenile growth rate (increment in mass), and oxygen consumption were measured at 15 and 25 degrees C in 21 clones from one northern and two southern sites. There were no significant differences in body size and growth rate (increase in length) at both 15 and 25 degrees C among the three sites. Clones from southern site 2 had a higher mass increment than clones from the other two sites at both temperatures. Clone had a significant effect on growth (body length) and body size at both temperatures. As expected, age at maturity was lower at 25 degrees C (4.5 days) than at 15 degrees C, (11.6 days) and body sizes, after the release of the third clutch, were larger at 15 degrees C than at 25 degrees C. Northern clones had higher oxygen consumption rates and specific dynamic action (SDA) than southern clones at 15 degrees C. By contrast, southern clones from site 1 had a higher oxygen consumption and SDA than subarctic clones at 25 degrees C. Clones from southern site 2 had high oxygen consumption rates at both temperatures. Our results reveal important differences in metabolic rates among Daphnia from different thermal regimes, which were not always reflected in growth rate differences.