We don’t know the half of it: morphological and molecular evidence reveal dramatic underestimation of diversity in a key pollinator group (Nemestrinidae)

Nemestrinidae (tangle-veined flies) are important pollinators of numerous southern African plant species. Despite their known ecological importance, the family has received little taxonomic attention in recent years and the systematics of the group is poorly understood. In this study we aimed to assess the phylogenetic relationships and species diversity among three southern African nemestrinid genera from the Nemestrininae subfamily: Prosoeca, Moegistorhynchus and Stenobasipteron, with a specific focus on the largest among these, Prosoeca. We reconstructed a molecular phylogeny using both mitochondrial and nuclear (COI, 16S rRNA, 28S rRNA and CAD) DNA sequence data. Both morphology and molecular species delimitation methods (Automatic Barcode Gap Discovery and the Bayesian Poisson Tree Process) were used to estimate species diversity. The topology from the combined analysis places a monophyletic Moegistorhynchus as the sister group to a paraphyletic Prosoeca with Stenobasipteron nested inside Prosoeca. In all three genera, almost half of the putative species sampled did not match the concept of described species based on morphology. Analysis of phylogenetic diversity showed that undescribed putative species make a substantial contribution to the overall phylogenetic diversity among the sampled species. Comparisons among biogeographic regions suggested that diversity is concentrated in multiple biodiversity hotspots and biomes, particularly in Fynbos and Grassland biomes. The numerous undescribed species and paraphyly of Prosoeca both emphasise the need for increased taxonomic attention for this ecologically important group of flies in particular, and for southern African insect taxa in general.