G. Henk Visser

Development of Temperature Regulation in Shorebirds

We studied the influence of body size on the development of temperature regulation in chicks of 10 North American and five European shorebird species belonging to the families Charadriidae and Scolopacidae. Neonatal body mass ranged between 4 and 55 g, and asymptotic body mass ranged between 20 and 650 g. We measured the change in body temperature of chicks individually exposed for 30 min to ambient temperatures of 2°, 10°, and 18°C. An index of homeothermy for each species at each ambient temperature increased as a linear function of the logarithm of body mass. Before achieving homeothermy at 18°C, chicks of small species almost tripled their body mass from hatching, whereas chicks of the largest species increased their body mass by only 10%. In the five European species we studied the development of resting and peak metabolic rate, and minimal thermal conductance, as a function of body mass. The development of homeothermy resulted mainly from a strong increase in the maximum mass-specific heatproduction due to thermogenesis (peak metabolic rate minus resting metabolic rate in the thermoneutral zone). The latter phenomenon is linked with a parallel reduction of the relative growth rate of the chick. These results are consistent with the hypothesis of Ricklefs (1979), who suggested that well-developed muscle function is incompatible with a high relative growth rate.

Behavioural and physiological responses to increased foraging effort in male mice

SUMMARY Free-living animals must forage for food and hence may face energetic constraints imposed by their natural environmental conditions (e.g. ambient temperature, food availability). Simulating the variation in such constraints, we have experimentally manipulated the rate of work (wheel running) mice must do to obtain their food, and studied the ensuing behavioural and physiological responses. This was done with a line of mice selectively bred for high spontaneous wheel running and a randomly bred control line that vary in the amount of baseline wheel-running activity. We first determined the maximum workload for each individual. The maximum workload animals could engage in was around 23 km d–1 in both control and activity-selected mice, and was not associated with baseline wheel-running activity. We then kept mice at 90% of their individual maximum and measured several physiological and behavioural traits. At this high workload, mice increased wheel-running activity from an average of 10 to 20 km d–1, and decreased food intake and body mass by approximately 20%. Mass-specific resting metabolic rate strongly decreased from 1.43 to 0.98 kJ g–1 d–1, whereas daily energy expenditure slightly increased from 2.09 to 2.25 kJ g–1 d–1. Costs of running decreased from 2.3 to 1.6 kJ km–1 between baseline and workload conditions. At high workloads, animals were in a negative energy balance, resulting in a sharp reduction in fat mass as well as a slight decrease in dry lean mass. In addition, corticosterone levels increased, and body temperature was extremely low in some animals at high workloads. When challenged to work for food, mice thus show significant physiological and behavioural adjustments.

Metabolism and Aging: Effects of Cold Exposure on Metabolic Rate, Body Composition, and Longevity in Mice

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.

Protein Synthesis and Antioxidant Capacity in Aging Mice: Effects of Long‐Term Voluntary Exercise

Exercise increases metabolic rate and the production of reactive oxygen species (ROS) but also elevates protein turnover. ROS cause damage to macromolecules (e.g., proteins) and thereby contribute to aging. Protein turnover removes and replaces damaged proteins. The balance between these two responses may underlie beneficial effects of physical activity on aging. Effects of lifelong exercise on antioxidant enzyme activities and fractional synthesis rate of protein (FSRP) were examined at various ages (2–26 mo) in heart, liver, and muscle of mice that had been selectively bred for high wheel‐running activity, housed with (S+) or without (S−) a running wheel, and their random‐bred controls (C+) housed with running wheels. FSRP decreased with age and increased in muscle of young, but not old, activity‐selected mice. Enzyme activity of superoxide dismutase and glutathione peroxidase decreased with age and showed a peak at 10 mo of age in liver. Selection for wheel‐running activity did not affect antioxidant enzyme activity. Daily energy expenditure correlated positively with antioxidant levels in liver. This might indicate that oxidative stress (ROS production) increases with metabolic rate, driving upregulation of antioxidant enzymes. Alternatively, the elevated energy expenditure may reflect the energetic cost of elevated protection, consistent with the disposable‐soma hypothesis and with other studies showing positive links between energy expenditure and life span. Long‐term elevations in voluntary exercise did not result in elevations in antioxidant enzyme activities or protein synthesis rates.

Water and Heat Balance during Flight in the Rose‐Colored Starling (Sturnus roseus)

Water imbalance during flight is considered to be a potentially limiting factor for flight ranges in migrating birds, but empirical data are scarce. We studied flights under controlled ambient conditions with rose‐colored starlings in a wind tunnel. In one experiment, we measured water fluxes with stable isotopes at a range of flight speeds (9–14 m s−1) at constant temperature (15°C). In a second experiment, we measured evaporation rates at variable ambient temperatures (ndocumentclass{aastex}nusepackage{amsbsy}nusepackage{amsfonts}nusepackage{amssymb}nusepackage{bm}nusepackage{mathrsfs}nusepackage{pifont}nusepackage{stmaryrd}nusepackage{textcomp}nusepackage{portland,xspace}nusepackage{amsmath,amsxtra}nusepackage[OT2,OT1]{fontenc}nnewcommandcyr{nrenewcommandrmdefault{wncyr}nrenewcommandsfdefault{wncyss}nrenewcommandencodingdefault{OT2}nnormalfontnselectfont}nDeclareTextFontCommand{textcyr}{cyr}npagestyle{empty}nDeclareMathSizes{10}{9}{7}{6}nbegin{document}nlandscapen

Evaluation of the Deuterium Dilution Method to Estimate Body Composition in the Barnacle Goose: Accuracy and Minimum Equilibration Time

T_{mathrm{a},}=5^{circ }{mbox{--}} 27^{circ }mathrm{C},

Female mice respond differently to costly foraging versus food restriction

nend{document} ) but constant speed (12 m s−1). During all flights, the birds experienced a net water loss. On average, water influx was 0.98 g h−1 (ndocumentclass{aastex}nusepackage{amsbsy}nusepackage{amsfonts}nusepackage{amssymb}nusepackage{bm}nusepackage{mathrsfs}nusepackage{pifont}nusepackage{stmaryrd}nusepackage{textcomp}nusepackage{portland,xspace}nusepackage{amsmath,amsxtra}nusepackage[OT2,OT1]{fontenc}nnewcommandcyr{nrenewcommandrmdefault{wncyr}nrenewcommandsfdefault{wncyss}nrenewcommandencodingdefault{OT2}nnormalfontnselectfont}nDeclareTextFontCommand{textcyr}{cyr}npagestyle{empty}nDeclareMathSizes{10}{9}{7}{6}nbegin{document}nlandscapen