Background: Ecological speciation is a process in which a transiently resource-polymorphic species divides into two specialized sister lineages as a result of divergent selection pressures caused by the use of multiple niches or environments. Ecology-based speciation has been studied intensively in plant-feeding insects, in which both sympatric and allopatric shifts onto novel host plants could speed up diversification. However, while numerous examples of species pairs likely to have originated by resource shifts have been found, the overall importance of ecological speciation in relation to other, non-ecological speciation modes remains unknown. Here, we apply phylogenetic information on sawflies belonging to the 'Higher' Nematinae (Hymenoptera: Tenthredinidae) to infer the frequency of niche shifts in relation to speciation events.
Recent phylogenetic studies on Nematinae based on DNA sequences have shown extensive incongruencies with current nomenclature of genus-group taxa. Here, we expand previous DNA sequence datasets based on three genes (CoI, Cytb, and EF-1α), to include a fourth (NaK) and more genera. The analyses largely confirm the previous findings, particularly the existence of two well-supported large clades, Euura and Pristiphora, together comprising more than 75% of the species of Nematinae. Basal relationships within these two clades remain poorly resolved, mirroring the difficulties in delimiting genera based on morphology. In addition, a moderately supported small clade, Nematus, is found. The relationships between the Euura, Pristiphora, and Nematus clades are uncertain. Therefore, to stabilize the nomenclature we treat these clades as genera. This taxonomic treatment results in numerous new combinations of species names. The following synonymies are
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