Selection does not favor larger body size at lower temperature in a seed-feeding beetle

R. Craig Stillwell, Jordi Moya-Laraño, Charles W. Fox

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Body size of many animals increases with increasing latitude, a phenomenon known as Bergmann's rule (Bergmann clines). Latitudinal gradients in mean temperature are frequently assumed to be the underlying cause of this pattern because temperature covaries systematically with latitude, but whether and how temperature mediates selection on body size is unclear. To test the hypothesis that the "relative" advantage of being larger is greatest at cooler temperatures we compare the fitness of replicate lines of the seed beetle, Stator limbatus, for which body size was manipulated via artificial selection ("Large," "Control," and "Small" lines), when raised at low (22°C) and high (34°C) temperatures. Large-bodied beetles (Large lines) took the longest to develop but had the highest lifetime fecundity, and highest fitness (rC), at both low and high temperatures. However, the relative difference between the Large and Small lines did not change with temperature (replicate 2) or was greatest at high temperature (replicate 1), contrary to the prediction that the fitness advantage of being large relative to being small will decline with increasing temperature. Our results are consistent with two previous studies of this seed beetle, but inconsistent with prior studies that suggest that temperature-mediated selection on body size is a major contributor to the production of Bergmann clines. We conclude that other environmental and ecological variables that covary with latitude are more likely to produce the gradient in natural selection responsible for generating Bergmann clines.

Original languageEnglish
Pages (from-to)2534-2544
Number of pages11
Issue number10
StatePublished - Oct 2008


  • Bergmann's rule
  • Body size
  • Latitudinal cline
  • Seed beetles
  • Temperature

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Genetics
  • General Agricultural and Biological Sciences


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