4.6 Article

The Influence of Modularity on Cranial Morphological Disparity in Carnivora and Primates (Mammalia)

Journal

PLOS ONE
Volume 5, Issue 3, Pages -

Publisher

PUBLIC LIBRARY SCIENCE
DOI: 10.1371/journal.pone.0009517

Keywords

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Funding

  1. U.S. National Science Foundation International Research Fellowship OISE [0502186]
  2. U.S. National Science Foundation DDIG [0308765]
  3. Field Museum Women-in-Science Fellowship
  4. Society of Vertebrate Paleontology Predoctoral Fellowship
  5. American Museum of Natural History Collections Study Grant
  6. University of California Samuel P. and Doris Welles Fund
  7. University of Chicago Hinds Fund
  8. Division Of Environmental Biology
  9. Direct For Biological Sciences [0308765] Funding Source: National Science Foundation
  10. Office Of Internatl Science &Engineering
  11. Office Of The Director [0502186] Funding Source: National Science Foundation

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Background: Although variation provides the raw material for natural selection and evolution, few empirical data exist about the factors controlling morphological variation. Because developmental constraints on variation are expected to act by influencing trait correlations, studies of modularity offer promising approaches that quantify and summarize patterns of trait relationships. Modules, highly-correlated and semi-autonomous sets of traits, are observed at many levels of biological organization, from genes to colonies. The evolutionary significance of modularity is considerable, with potential effects including constraining the variation of individual traits, circumventing pleiotropy and canalization, and facilitating the transformation of functional structures. Despite these important consequences, there has been little empirical study of how modularity influences morphological evolution on a macroevolutionary scale. Here, we conduct the first morphometric analysis of modularity and disparity in two clades of placental mammals, Primates and Carnivora, and test if trait integration within modules constrains or facilitates morphological evolution. Principal Findings: We used both randomization methods and direct comparisons of landmark variance to compare disparity in the six cranial modules identified in previous studies. The cranial base, a highly-integrated module, showed significantly low disparity in Primates and low landmark variance in both Primates and Carnivora. The vault, zygomatic-pterygoid and orbit modules, characterized by low trait integration, displayed significantly high disparity within Carnivora. 14 of 24 results from analyses of disparity show no significant relationship between module integration and morphological disparity. Of the ten significant or marginally significant results, eight support the hypothesis that integration within modules constrains morphological evolution in the placental skull. Only the molar module, a highly-integrated and functionally important module, showed significantly high disparity in Carnivora, in support of the facilitation hypothesis. Conclusions: This analysis of within-module disparity suggested that strong integration of traits had little influence on morphological evolution over large time scales. However, where significant results were found, the primary effect of strong integration of traits was to constrain morphological variation. Thus, within Primates and Carnivora, there was some support for the hypothesis that integration of traits within cranial modules limits morphological evolution, presumably by limiting the variation of individual traits.

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