A strong response to selection on mass-independent maximal metabolic rate without a correlated response in basal metabolic rate.

Metabolic rates are correlated with many aspects of ecology, but how selection on different aspects of metabolic rates affects their mutual evolution is poorly understood. Using laboratory mice, we artificially selected for high maximal mass-independent metabolic rate (MMR) without direct selection on mass-independent basal metabolic rate (BMR). Then we tested for responses to selection in MMR and correlated responses to selection in BMR. In other lines, we antagonistically selected for mice with a combination of high mass-independent MMR and low mass-independent BMR. All selection protocols and data analyses included body mass as a covariate, so effects of selection on the metabolic rates are mass adjusted (that is, independent of effects of body mass). The selection lasted eight generations. Compared with controls, MMR was significantly higher (11.2%) in lines selected for increased MMR, and BMR was slightly, but not significantly, higher (2.5%). Compared with controls, MMR was significantly higher (5.3%) in antagonistically selected lines, and BMR was slightly, but not significantly, lower (4.2%). Analysis of breeding values revealed no positive genetic trend for elevated BMR in high-MMR lines. A weak positive genetic correlation was detected between MMR and BMR. That weak positive genetic correlation supports the aerobic capacity model for the evolution of endothermy in the sense that it fails to falsify a key model assumption. Overall, the results suggest that at least in these mice there is significant capacity for independent evolution of metabolic traits. Whether that is true in the ancestral animals that evolved endothermy remains an important but unanswered question.

On-line computerized data handling system for treating patients with renal disease.

Some patients with renal disease accrue 6,000 to 8,000 individual data items relating to symptoms, signs, laboratory information, and treatment in one year. To deal with the problem of handling so many data items, the following steps were taken: (1) a dictionary of terms peculiar to nephrology was created; (2) manual time-oriented records for nephrology were constructed; and (3) an on-line data processing system, using a PDP-11/70 computer and remote teleprocessing terminal, was developed. On the terminal screen, up to 11 consecutive patient visits can be displayed horizontally, with 18 data items displayed vertically. Up to 30 of the most recent patient visits are easily accessible. For patient treatment, a special feature allows a rearrangement and instantaneous display of any combination of data, thus permitting review of essential feedback relationships between clinical events and treatment.

Scaling the duration of activity relative to body mass results in similar locomotor performance and metabolic costs in lizards.

This study examines the physiological response to locomotion in lizards following bouts of activity scaled to body mass. We evaluate this method as a way to compare locomotor energetics among animals of varying body mass. Because most of the costs of brief activity in reptiles are repaid during recovery we focus on the magnitude and duration of the excess post-exercise oxygen consumption (EPOC). Lizards ranging from 3 g to 2400 g were run on a treadmill for durations determined by scaling the run time of each animal to the 1/4 power of body mass and allowing each animal to run at its maximum speed for that duration. This protocol resulted in each species traveling the same number of body lengths and incurring similar factorial increases in V(O(2)). Following activity, EPOC volume (ml O(2)) and the cost of activity per body length traveled (ml O(2) per body length) scaled linearly with body mass. This study shows that the mass-specific costs of activity over an equivalent number of body lengths are similar across a broad range of body mass and does not show the typical patterns of allometric scaling seen when cost of locomotion are expressed on a per meter basis. Under field conditions larger animals are likely to travel greater absolute distances in a given bout of activity than smaller animals but may travel a similar number of body lengths. This study suggests that if locomotor costs are measured on a relative scale (ml O(2) per body length traveled), which reflects these differences in daily movement distances, that locomotor efficiency is similar across a wide range of body mass.

Evidence for facilitated lactate uptake in lizard skeletal muscle.

To understand more fully lactate metabolism in reptilian muscle, lactate uptake in lizard skeletal muscle was measured and its similarities to the monocarboxylate transport system found in mammals were examined. At 2 min, uptake rates of 15 mmol l(-1) lactate into red iliofibularis (rIF) were 2.4- and 2.2-fold greater than white iliofibularis (wIF) and mouse soleus, respectively. alpha-Cyano-4-hydroxycinnamate (15 mmol l(-1)) caused little inhibition of uptake in wIF but caused a 42-54 % reduction in the uptake rate of lactate into rIF, suggesting that much of the lactate uptake by rIF is via protein-mediated transport. N-ethymaleimide (ETH) (10 mmol l(-1)) also caused a reduction in the rate of uptake, but measurements of adenylate and phosphocreatine concentrations show that ETH had serious effects on rIF and wIF and may not be appropriate for transport inhibition studies in reptiles. The higher net uptake rate by rIF than by wIF agrees with the fact that rIF shows much higher rates of lactate utilization and incorporation into glycogen than wIF. This study also suggests that lactate uptake by reptilian muscle is similar to that by mammalian muscle and that, evolutionarily, this transport system may be relatively conserved even in animals with very different patterns of lactate metabolism.