Rejection of non-adaptive hypotheses for intraspecific variation in trophic morphology in gape-limited predators

Anders Forsman*, Richard Shine

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)

Abstract

Recent studies have interpreted intraspecific divergence in relative head sizes in snakes as evidence for adaptation of the trophic apparatus in gape-limited predators to local prey size. However, such variation might also arise from non-adaptive processes (such as allometry, correlated response, genetic drift, or non-adaptive phenotypic plasticity). We test predictions from these alternative hypotheses using data on the allometric relationship between head size and body size in two wide-ranging snake species: eight populations of adders (Vipera berus) and 30 populations of common gartersnakes (Thamnophis sirtalis). Our data enable strong rejection of the alternative (non-adaptive) hypotheses, because the relationship between head and body size differed significantly among populations, the geographic distance separating pairs of populations explained less than 1.5% of their divergence in allometric coefficients, and the within-population allometric coefficients were higher than the among-population coefficients in each species. In addition, the geographical variability of allometric coefficients in females did not parallel that in males, suggesting that allometric coefficients have evolved independently in the two sexes. Phenotypic plasticity also cannot explain the data, because laboratory studies show that the allometric relationship between head size and body size is relatively insensitive to differing growth rates. We conclude that the intraspecific head size divergence in these snakes is better explained by spatially heterogeneous selection to optimize prey handling ability, than by non-adaptive processes.

Original languageEnglish
Pages (from-to)209-223
Number of pages15
JournalBiological Journal of the Linnean Society
Volume62
Issue number2
DOIs
Publication statusPublished - Oct 1997
Externally publishedYes

Keywords

  • Allometry
  • Correlated response
  • Divergence
  • Evolution
  • Feeding habits
  • Geographic variation
  • Phenotypic plasticity
  • Snakes

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