Geographic variation in body size and sexual size dimorphism of north american ratsnakes (Pantherophis spp. s.l.)

Brett A. Degregorio, Gabriel Blouin-Demers, Gerardo L.F. Carfagno, J. Whitfield Gibbons, Stephen J. Mullin, Jinelle H. Sperry, John D. Willson, Kenny Wray, Patrick J. Weatherhead

Research output: Contribution to journalArticlepeer-review


Because body size affects nearly all facets of an organism’s life history, ecologists have long been interested in large-scale patterns of body-size variation, as well as why those large-scale patterns often differ between sexes. We explored body-size variation across the range of the sexually dimorphic Ratsnake complex (species of the genus Pantherophis Fitzinger, 1843 s.l.; formerly Elaphe obsoleta (Say in James, 1823)) in North America. We specifically explored whether variation in body size followed latitudinal patterns or varied with climatic variables. We found that body size did not conform to a climatic or latitudinal gradient, but instead, some of the populations with the largest snakes occurred near the core of the geographic range and some with the smallest occurred near the northern, western, and southern peripheries of the range. Males averaged 14% larger than females, although the degree of sexual size dimorphism varied between populations (range: 2%–25%). There was a weak trend for male body size to change in relation to temperature, whereas female body size did not. Our results indicate that relationships between climate and an ectotherm’s body size are more complicated than linear latitudinal clines and likely differ for males and females.

Original languageEnglish (US)
Pages (from-to)1196-1202
Number of pages7
JournalCanadian journal of zoology
Issue number11
StatePublished - 2018


  • Bergmann’s rule
  • Body size
  • Climatic variability
  • Latitudinal clines
  • North American Ratsnake
  • Pantherophis spp
  • Sexual dimorphism
  • Temperature

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Animal Science and Zoology


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