Origin of obligate dim-light foraging in nomiine sweat bees (Halictidae: Nomiinae), with the description of a new species of Mellitidia

Dim-light foraging is exhibited by the majority of the seven bee families (facultative behavior—five families; obligate behavior – four families) and represents an underappreciated aspect of pollination ecology. The most diverse adaptive radiations occur within the family Halictidae and while neotropical augochlorine bees (Halictinae) have been well studied, very little is known about an independent paleotropical origin of nomiine dim-light bee foraging (Nomiinae) restricted to Australasia (New Guinea and Australia). Here we provide the first molecular systematic hypothesis for the obligate dim-light genus Reepenia and its closest diurnal relatives derived from ultraconserved elements and whole genome sequence data: (Paulynomia, (Austronomia, (Mellitidia (Reepenia, Ptilonomia)))). Relaxed-clock divergence estimates suggest a Miocene origin for this Australo-Papuan endemic clade of Nomiinae (~ 20 mya, 95% CI 11–35) and the most recent common ancestor of Reepenia + Ptilonomia (~ 7 mya, 95% CI 2.82–16.7); with a Pleistocene/Pliocene crown age for Reepenia (~ 2 mya, 95% CI 0.83–6.22). Integrative taxonomic inference yielded the discovery of Mellitidia glossata Bossert sp. nov., which is described and illustrated herein.