Legs of deception: disagreement between molecular markers and morphology of long‐legged flies (Diptera,Dolichopodidae)

Conflicting hypotheses in phylogenetics and systematics, generated by different data sets (e.g. morphological versus molecular), are common in biology. The clarification of such instances may allow understanding general mechanisms involved in the speciation process in an evolutionary light. Here, we present and discuss the case of the Dolichopus plumipes species group in the long‐legged flies, Dolichopodidae. A phylogenetic survey was performed based on both morphological and molecular data. The full data set comprises 31 morphological characters and 2252 molecular characters (mitochondrial – COI: 810; 12S: 343; 16S: 514; nuclear – ITS2: 585) of 49 different species, represented by 82 specimens. The molecular phylogenetic analysis revealed a clade (composed by the species D. plumipes, Dolichopus wahlbergi, Dolichopus polleti, Dolichopus simplex, and Dolichopus nigricornis) that disagrees with the traditional morphological view based on external characters. In particular, specimens of the species D. plumipes and D. simplex were indistinguishable with the molecular markers used here. Yet, we still consider D. plumipes and D. simplex as two distinct taxa and provide explanatory hypotheses on the evolutionary background. The conspicuous male secondary sexual characters (present in plumipes but not in simplex) are key factors in sexual selection and their presumably rapid reduction in D. simplex is thought to be of main importance for the explanation of the speciation process. The plumipes–simplex case may therefore be viewed as a paradigmatic illustration showing that a better integration of the molecular and morphological approaches is needed to understand and clarify the, in some cases, complex systematics and phylogeny of organisms.