Resting and daily energy expenditures of free-living field voles are positively correlated but reflect extrinsic rather than intrinsic effects

John Roger Speakman, T. Ergon, R. Cavanagh, Karen Reid, D. M. Scantlebury, Xavier Lambin

Research output: Contribution to journalArticle

83 Citations (Scopus)

Abstract

Resting metabolic rates at thermoneutral (RMRts) are unexpectedly variable. One explanation is that high RMRts intrinsically potentiate a greater total daily energy expenditure (DEE), but recent work has suggested that DEE is extrinsically defined by the environment, which independently affects RMRt. This extrinsic effect could occur because expenditure is forced upwards in poor habitats or enabled to rise in good habitats. We provide here an intraspecific test for an association between RMRt and DEE that separates intrinsic from extrinsic effects and forcing from enabling effects. We measured the DEE and RMRt of 75 free-living short-tailed field voles at two time points in late winter. Across all sites, there was a positive link between individual variation in RMRt and DEE. This correlation, however, emerged only because of an effect across sites, rather than because of an intrinsic association within sites. We defined site quality from the survivorship of voles at the sites and the time at which they commenced breeding in spring. The associations between DEE/RMRt and site quality suggested that in February voles in poorer sites had higher energy demands, indicating that DEE was forced upwards, but in March the opposite was true, with higher demands in good sites, indicating that high expenditure was enabled. These data show that daily energy demands are extrinsically defined, with a link to RMRt that is secondary or independent. Both forcing and enabling effects of the environment may pertain at different times of year.

Original languageEnglish
Pages (from-to)14057-14062
Number of pages5
JournalPNAS
Volume100
Issue number24
DOIs
Publication statusPublished - Nov 2003

Keywords

  • MICE PEROMYSCUS-MANICULATUS
  • BASAL METABOLIC-RATE
  • LIFE-HISTORY TRAITS
  • MUS MUSCULUS
  • MICROTUS-AGRESTIS
  • LACTATING MICE
  • INTRASPECIFIC VARIATION
  • SIGMODON-HISPIDUS
  • COLD-EXPOSURE
  • COTTON RAT

Cite this

Resting and daily energy expenditures of free-living field voles are positively correlated but reflect extrinsic rather than intrinsic effects. / Speakman, John Roger; Ergon, T.; Cavanagh, R.; Reid, Karen; Scantlebury, D. M.; Lambin, Xavier.

In: PNAS, Vol. 100, No. 24, 11.2003, p. 14057-14062.

Research output: Contribution to journalArticle

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AU - Reid, Karen

AU - Scantlebury, D. M.

AU - Lambin, Xavier

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AB - Resting metabolic rates at thermoneutral (RMRts) are unexpectedly variable. One explanation is that high RMRts intrinsically potentiate a greater total daily energy expenditure (DEE), but recent work has suggested that DEE is extrinsically defined by the environment, which independently affects RMRt. This extrinsic effect could occur because expenditure is forced upwards in poor habitats or enabled to rise in good habitats. We provide here an intraspecific test for an association between RMRt and DEE that separates intrinsic from extrinsic effects and forcing from enabling effects. We measured the DEE and RMRt of 75 free-living short-tailed field voles at two time points in late winter. Across all sites, there was a positive link between individual variation in RMRt and DEE. This correlation, however, emerged only because of an effect across sites, rather than because of an intrinsic association within sites. We defined site quality from the survivorship of voles at the sites and the time at which they commenced breeding in spring. The associations between DEE/RMRt and site quality suggested that in February voles in poorer sites had higher energy demands, indicating that DEE was forced upwards, but in March the opposite was true, with higher demands in good sites, indicating that high expenditure was enabled. These data show that daily energy demands are extrinsically defined, with a link to RMRt that is secondary or independent. Both forcing and enabling effects of the environment may pertain at different times of year.

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KW - LIFE-HISTORY TRAITS

KW - MUS MUSCULUS

KW - MICROTUS-AGRESTIS

KW - LACTATING MICE

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KW - COLD-EXPOSURE

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