Metabolic rate depression is induced by caloric restriction and correlates with rate of development and lifespan in a parthenogenetic insect

Caloric restriction (CR) extends lifespan in most animals, but the mechanisms underlying this phenomenon are the subject of much debate. We investigated the association between longevity and resting metabolic rate (RMR) in Indian stick insects (Carausius morosus) by (i) determining the appropriate scaling coefficient for calculating mass-corrected RMR of insects throughout development, (ii) quantifying the response of RMR to diet history, and (iii) correlating RMR in multiple life-history stages with adult and total lifespan. Over a range of body sizes, whole-body RMR (measured as oxygen consumption rate) scaled linearly with body mass. Mass-specific RMR decreased in response to CR, particularly when food was restricted during juvenile stages. With one exception, RMR of insects in different life-history stages matched current feeding level and was not substantially affected by intake history. Total lifespan was affected by intake, with insects that experienced CR early in development living longer than insects that were fed ad libitum. Although CR was associated with extended total lifespan and decreased RMR, it was also associated with shortened adult lifespan. Thus, we found limited evidence that decreased RMR plays a causative role in determining longevity. Instead, CR and decreased RMR were associated with slower progression through pre-reproductive life-history stages. (C) 2009 Elsevier Inc. All rights reserved.