Effect of taxon sampling in morphological phylogenetic analyses: Insights from three Diptera taxa with different diversification rates

Taxon sampling is an integral and important part of any phylogenetic analysis. Testing the monophyly of previously established taxa by including more than one representative species is an obvious and important task. The present analysis will study the effect of taxon sampling in three taxa of flies (Diptera) that together form a clade. Apioceridae (flower-loving flies), Asilidae (robber flies), and Mydidae (mydas flies) share a Cetaceous-age common ancestor, but have since diversified very differently into 138, more than 7,500, and 473 currently known species, respectively. Therefore, the density of sampling and number of taxa included in analyses to elucidate the phylogenetic relationships within each family will be different based on available material and the effects of taxon sampling could vary. Over the past few years, morphological character matrices for all three families have been developed based on a comprehensive taxon sampling approach. Here, the topological results as well as character and branch support for certain clades are compared between the original, complete taxon matrix hypothesis of relationships to hypotheses derived from the analysis of either reduced or increased taxon matrices. Two scenarios are studied: (1) a posteriori taxon exclusion through removal of species from taxa that are represented by more than one species and (2) a posterior taxon inclusion through the addition of representatives to higher-level taxa that have previously only been represented by a single species.