Natural Selection

Figure 5 Comparison of conventional and phylogenetic regression analyses. Phylogeny of six terminal taxa (TA-TF) and two outgroup taxa (O1 and O2), represented by two continuously distributed characters (C1 and C2). Tree topology determined from data other than characters 1 and 2, and branch lengths treated as equal. Seven internal tree nodes represented by ancestral taxa (AG-AM) with ancestral trait values estimated by least-squares parsimony. a, Conventional regression of trait values from terminal taxa. b, Phylogenetic regression of trait values at internal tree nodes using the method of independent contrasts. Note that by removing psuedoreplicates, the phylogenetic regression compares fewer taxa, has fewer degrees of freedom, and has a lower correlation coefficient (R2 value) than does the conventional regression. The phylogenetic regression, therefore, provides a more conservative quantitative measure of correlated evolution between the two traits.

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