Daily energy expenditure during lactation is strongly selected in a free-living mammal

Quinn E. Fletcher*, John R. Speakman, Stan Boutin, Jeffrey E. Lane, Andrew G. Mcadam, Jamieson C. Gorrell, David W. Coltman, Murray M. Humphries

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


Energy expenditure is a trait of central importance in ecological and evolutionary theory. We examined the correlates of, the strength of selection on, and the heritability of, daily energy expenditure (DEE; kJ day-1) during lactation in free-ranging North American red squirrels (Tamiasciurus hudsonicus). Over 7 years, lactating squirrels with greater DEE had higher annual reproductive success (ARS; standardized selection gradient: β' = 0·47; top 12% of published estimates). Surprisingly, positive fecundity selection on lactation DEE for increased ARS did not result because lactation DEE was correlated with typical measures of reproductive performance and/or investment. We found no evidence of costs of elevated lactation DEE acting through female survival, subsequent year lactation DEE or subsequent year reproduction. Lactation DEE was not significantly repeatable, and heritability was not significantly different from zero. Elevated lactation DEE enhances ARS through a link between DEE and an unidentified measure of maternal or environmental quality, but there is limited evolutionary potential for lactation DEE to respond to our documented selection.

Original languageEnglish
Pages (from-to)195-208
Number of pages14
JournalFunctional Ecology
Issue number2
Early online date21 Jul 2014
Publication statusPublished - 1 Feb 2015

Bibliographical note

Funded by
Natural Sciences and Engineering Council of Canada (NSERC)
National Science Foundation and Northern Scientific Training Program Grants
NSERC Postgraduate Graduate Scholarship


  • Costs of reproduction
  • Energetics
  • Heritability
  • Reproductive success


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