Live fast, Die Young? Theory-higher metabolism means a shorter lifespan 1920s proposed aging is a by-product of energy expenditure Hence faster you use energy, faster you age, sooner you die Known as “rate-of-living” theory

In recent times comparison of animals groups cast doubt Birds have a higher metabolism than mammals, yet live much longer Question 1-in the above comparison what factor would have been important? Birds and mammals would have been of similar size Live fast, Die Young?

Lobke Vaanholt just completed a study Investigated the theory not across species but within a species-mice Question 2-What might they have done? Think about a possible experimental set up. Live fast, Die Young?

Question 3-What’s the first and most important thing in the design of the experiment? Two groups of mice were used Question 4-How old would they have been? For how long would the experiment have been done? Study done from birth to death Live fast, Die Young?

Question 5-So what would have been different between the two groups? One group would have had to use more energy to live compared to the other group Question 6-How did they go about doing this? They were kept at different temperatures for their entire lives One group at 22 o C, the other at 10 o C. Question 7-Why 22 o C? Live fast, Die Young?

Question 8-Why would different environmental temperatures be useful? Mammals expend energy to maintain their body temperature of 37 o C. Question 9-What would have been different about the two groups of mice? The colder group would have to spend more energy to maintain their body temperature. Live fast, Die Young?

Question 10-In what ways would the colder group spend more energy? More shivering Being more active Eating more Live fast, Die Young?

Question 11-Would they have taken measurements of any sort or would they have just seen how long they lived for? Took measurements of Overall daily energy expenditure and Mass-specific energy expenditure throughout adult life Question 12-Why the second one? Because the mass of the mice on the two groups may have changed differently as a result of their environment and lifestyle and this could also affect their total energy use. Live fast, Die Young?

Question 13-So what results would you expect in relation to the energy use measurements? Higher energy use for both measurements in the colder group Found that colder group had a: 48% increase in overall daily energy expenditure 64% increase in mass-specific energy expenditure during adult life Live fast, Die Young?

Question 14-Now, what results would support the rate-of living theory? Life span of colder group was significantly lower than warmer group Question 15-What results would go against the theory? Both groups would on average have had an equal life span Question 16-What do you think they found? The latter Live fast, Die Young?

Question 17-What factors, if any, would they need to have controlled? What other questions do you have about the experiment? Are there any aspects of the experiment that could lead to error? Live fast, Die Young?

In a prior experiment Vaanholt had used exercise, instead of temperature as the source of increased energy expenditure In that experiment life span was not affected adversely by using more energy as a result of exercising more Question 18-Why might this not be as good an experiment as the one that used temperature? The benefit of exercise might be counteracting the effect of using more energy during the life Live fast, Die Young?

Abstract The proposition that increased energy expenditure shortens life has a long history. The rate-of- living theory (Pearl 1928) states that life span and average mass-specific metabolic rate are inversely proportional. Originally based on interspecific allometric comparisons between species of mammals, the theory was later rejected on the basis of comparisons between taxa (e.g., birds have higher metabolic rates than mammals of the same size and yet live longer). It has rarely been experimentally tested within species. Here, we investigated the effects of increased energy expenditure, induced by cold exposure, on longevity in mice. Longevity was measured in groups of 60 male mice maintained at either 22°C (WW) or 10°C (CC) throughout adult life. Forty additional mice were maintained at both of these temperatures to determine metabolic rate (by stable isotope turnover, gas exchange, and food intake) as well as the mass of body and organs of subsets of animals at four different ages. Because energy expenditure might affect longevity by either accumulating damage or by instantaneously affecting mortality rate, we included a third group of mice exposed to 10°C early in life and to 22°C afterward (CW). Exposure to cold increased mean daily energy expenditure by ca. 48% (from 47.8 kJ d−1 in WW to 70.6 kJ d−1 in CC mice, with CW intermediate at 59.9 kJ d−1). However, we observed no significant differences in median life span among the groups (WW, 832 d; CC, 834 d; CW, 751 d). CC mice had reduced body mass (lifetime mean 30.7 g) compared with WW mice (33.8 g), and hence their lifetime energy potential (LEP) per gram whole-body mass had an even larger excess than per individual. Greenberg (1999) has pointed out that the size of the energetically costly organs, rather than that of the whole body, may be relevant for the rate-of-living idea. We therefore expressed LEP also in terms of energy expenditure per gram dry lean mass or per gram “metabolic” organ mass (i.e., heart, liver, kidneys, and brain). No matter how it was expressed, LEP in CC mice significantly exceeded that of WW mice. This result demonstrates that increased energy expenditure does not shorten life span and adds evidence to the intraspecific refutation of the rate-of-living theory. We suggest that increased energy expenditure has both positive and negative effects on different factors determining life span and that the relationship between energy turnover and longevity is fundamentally nonmonotonic