Failure of the ILD to determine data combinability for slow loris phylogeny

Tests for incongruence as an indicator of among-data partition conflict hav e played an important role in conditional data combination. When such tests reveal significant incongruence, this has been interpreted as a rationale for not combining data into a single phylogenetic analysis. In this study o f lorisiform phylogeny, we use the incongruence length difference (ILD) tes t to assess conflict among three independent data sets. A large morphologic al data set and two unlinked molecular data sets-the mitochondrial cytochro me b gene and the nuclear interphotoreceptor retinoid binding protein (exon 1)-are analyzed with various optimality criteria and weighting mechanisms to determine the phylogenetic relationships among slow lorises (Primates, L oridae). When analyzed separately, the morphological data show impressive s tatistical support for a monophyletic Loridae. Both molecular data sets res olve the Loridae as paraphyletic, though with different branching orders de pending on the optimality criterion or character weighting used. When the t hree data partitions are analyzed in various combinations, an inverse relat ionship between congruence and phylogenetic accuracy is observed. Nearly al l combined analyses that recover monophyly indicate strong data partition i ncongruence ( P = 0.00005 in the most extreme case), whereas all analyses t hat recover paraphyly indicate lack of significant incongruence. Numerous l ines of evidence verify that monophyly is the accurate phylogenetic result. Therefore, this study contributes to a growing body of information affirmi ng that measures of incongruence should not be used as indicators of data s et combinability.