Resolving conflict and outgroup sampling in the diachlorine grade; a new classification system for Tabaninae (Diptera: Tabanidae)

The Diachlorini (Tabanidae: Tabaninae), as currently circumscribed, includes more genera and morphological variation than any other horse fly tribe. The 915 described species in this cosmopolitan but predominantly Neotropical and Australasian group include some of the only horse flies with phytophagous larvae and iridescent, wasp mimicking, host-specific, nocturnal feeding, or long tongued adults. Phylogenetic analyses from various data sources always show Diachlorini to be a paraphyletic grade, a progression of relationships including two other diverse and morphologically distinct tribes, Tabanini and Haematopotini. Our current phylogenetic work reveals ten monophyletic diachlorine genus groups, at least six of which should be raised to a suprageneric status to inform a more robust classification of Tabaninae. However, mitochondrial, nuclear ribosomal, nuclear protein coding, and morphological data contrast in their support for relationships between these genus groups. Taxon choice among sampled tabanine outgroups also affects the topology of the diachlorines. Here, we present and compare several outgroup sampling strategies to resolve data conflict and assess alternative support for relationships across data types. Regional, morphology-, and taxonomy-based taxon sampling are compared for their effects on ingroup relationships. Detailed investigation of alternative sources of evidence, taxon sampling and analytical approach greatly improves understanding of horse fly phylogeny, provides data useful for discerning morphological patterns, and leads to a more robust natural classification.