Metabolic consequences of hard work

Abstract

When an animal has to meet increased demands on its working capacity, for example, for thermoregulation or parental care, two strategies are available. The animal can reallocate energy from costly maintenance processes - such as immunological defence or DNA repair systems (compensation hypothesis) - or it may try to increase the rate of energy intake or efficiency of digestion by increasing the size of the alimentary tract (increased-intake hypothesis). By manipulating brood size, I affected parental effort among marsh tits (Parus palustris) as demonstrated by a significant increase in parental feeding rate with experimental brood size. Basal metabolic rate (BMR) increased both with manipulated brood size and individual feeding rate, supporting the predictions from the increased-intake hypothesis. Furthermore, I found a direct positive relation between BMR and energy expenditure, measured with the help of the doubly labelled water technique. The cost of achieving a higher working capacity is substantial since BMR increases more quickly than the surplus energy available for work. Since the cost of a high sustained workload was not primarily dependent on a reallocation of energy away from maintenance, such a cost should be searched for among the detrimental effects of a high metabolic rate per se, for example, an increased oxidative damage to DNA, proteins and lipids.

Early nutrition and phenotypic development: ‘catch-up’ growth leads to elevated metabolic rate in adulthood

“…The longer term consequences of this variation in metabolic rate will also be of interest since RMR is a major contributor to overall energy costs (Hulbert & Else 2004); a high RMR therefore increases the daily food requirement but may also allow a greater workload at peak times ( Nilsson 2002). Moreover, RMR has been implicated in the rate of senescence.…”

Costly steroids: egg testosterone modulates nestling metabolic rate in the zebra finch

“…Increased requirements for energy expenditure often translate into higher RMR (Nilsson 2002) and, thus, higher RMR in T-chicks may have resulted from higher levels of (begging) activity. Unfortunately, we have no data available on the begging activity of our chicks and, thus, we do not know whether T-chicks begged indeed longer or more intensely than controls.…”

Analysis of the effects of inbreeding on lifespan and starvation resistance in Drosophila melanogaster

“…Whether good quality individuals have higher or lower rate of metabolism is however still an unresolved question (Hawkins and Day 1999;Konarzewski and Diamond 1995;Reinhold 1999;Nilsson 2002;Rantala and Roff 2006;Johnston et al 2007;Ketola and Kotiaho 2009a, b;Mikkelsen et al 2010). The environment in which a population has evolved to live may have fundamental effects on its metabolic strategy in the sense that a low metabolic rate is favored in areas where food supply is scarce, while high metabolic rate is favored in areas where food supplies are abundant (Mueller and Diamond 2001).…”