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Keywords:

  • Coevolution;
  • Spatial autocorrelation;
  • Aphids

Abstract

The geographic covariation of the eastern cottonwood Populus deltoides with three different gallforming aphids in the genus Pemphigus is studied over eastern North America. Ten vegetative Populus characters were analyzed together with 32 stem mother, slate und gall dimension characters in Pemphigus populicaulis und in two morphs of P. populitransversus. The number of locality samples studied ranges from 56 to 157. The covariation between host und parasite characters was examined by correlation analysis und canonical correlations und shown to be slight. Multiple regressions of factor scores of Pemphigus variables on Populus characters show relatively low percentages of explained variance und few significant partial regression coefficients. Spatial autocorrelation analyses of Pemphigus factor scores und of their residuals on Populus variables demonstrated largely independent spatial structure of the two sets of variables. These findings were confirmed by multiple Mantel tests of distance matrices based on cottonwood und aphid phenetics und on geography. The undoubtedly close Pemphigus-Populus coevolution over geological time is not reflected in the microevolutionary variation over geographic space. Possible esplanations for these surprising findings are discussed.