Support for the refugia within refugia hypothesis in a North American cleptoparasitic bee. Nomada articulata

The genus Nomada is the most diverse and specious of the cleptoparasitic bees, yet very little is known about their population dynamics. Studying Nomada populations can be difficult since they occur in small numbers within the landscape; however, some species are abundant enough that studying their populations is possible. Nomada articulata Smith, 1854 is a common nest parasite of Agapostemon virescens (Fabricius, 1775) and Agapostemon sericeus (Forster, 1771) and is found throughout the US and Canada. We selected 74 individuals to explore the genetic structure and diversity of N. articulata across North America. In addition, phylogenetic trees were constructed using ultraconserved elements (UCEs) and mitochondrial DNA to test the relationship between the different individuals and regions. Our data suggests that N. articulata may be a species complex, as half of the specimens from the southern US fell outside teh N. articulata clade on both our UCE and mitochondrial trees. Nomada articulata has an excess of heterozygotes and low levels of inbreeding. We found the presence of two genetic clusters across the species' range one representing a western population and one comprising of the remaining three geographic regions. Division between the western population and all others is likely the result of glacier runoff flooding the Mississippi River during the end of the Last Glacial Maximum. We present here the first phylogeography for a Nomada species and provide a foundation for understanding how cleptoparasitic bee populations have responded to environmental changes over time.