Failure of the ILD to Determine Data Combinability for Slow Loris Phylogeny

Abstract

Tests for incongruence as an indicator of among-data partition con ict have played an important role in conditional data combination.When such tests reveal signi cant incongruence, this has been interpreted as a rationale for not combining data into a single phylogenetic analysis.In this study of lorisiform phylogeny, we use the incongruence length difference (ILD) test to assess con ict among three independent data sets.A large morphological data set and two unlinked molecular data sets-the mitochondrial cytochrome 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, Loridae).When analyzed separately, the morphological data show impressive statistical support for a monophyletic Loridae.Both molecular data sets resolve the Loridae as paraphyletic, though with different branching orders depending on the optimality criterion or character weighting used.When the three data partitions are analyzed in various combinations, an inverse relationship between congruence and phylogenetic accuracy is observed.Nearly all combined analyses that recover monophyly indicate strong data partition incongruence (P D 0:00005 in the most extreme case), whereas all analyses that recover paraphyly indicate lack of signi cant incongruence.Numerous lines of evidence verify that monophyly is the accurate phylogenetic result.Therefore, this study contributes to a growing body of information af rming that measures of incongruence should not be used as indicators of data set combinability. [Conditional data combination; galagos; incongruence length difference; lorises; molecules and morphology; partition homogeneity test.]The slow lorises (family Loridae; Gray, 1821) make up the most securely diagnosed clade in the entire primate radiation, both extant and extinct.These animals are distinguished from other primates by a spectacular array of behavioral, morphological, physiological, and ecological characteristics.A partial list of these characteristics includes fewer caudal vertebrae, more numerous thoracic vertebrae, transpedicular foramina of the thoracic vertebrae, shortened second digit of the hands and feet, retia mirabilia of the proximal limb vessels, large humeral and femoral articulations, highly mobile ankles and wrists, frontated and upwardly rotated orbits, specialized scent glands, slow methodical locomotion, digestive specializations for the consumption of toxic prey, and reduced basal metabolic rate (Charles-Dominique, 1977;