Several recent studies investigating patterns of diversification in widespread desert-adapted vertebrates have associated major periods of genetic differentiation to late Neogene mountain-building events; yet few projects have addressed these patterns in widespread invertebrates. We examine phylogeographic patterns in the widespread antlion species Brachynemurus sackeni Hagen (Neuroptera: Myrmeleontidae) using a region of the mitochondrial gene cytochrome oxidase I (COI). We then use a molecular clock to estimate divergence dates for the major lineages. Our analyses resulted in a phylogeny that shows two distinct lineages, both of which are likely distinct species. This reveals the first cryptic species-complex in Myrmeleontidae. The genetic split between lineages dates to about 3.8–4.7 million years ago and may be associated with Neogene mountain building. The phylogeographic pattern does not match patterns found in other taxa. Future analyses within this species-complex may uncover a unique evolutionary history in this group. 1. Introduction Phylogeographic analyses investigate the relationship between genealogies and their geographic distribution [1]. Many recent studies have investigated the historical biogeography of the Nearctic arid lands through the phylogeographic analyses of wide-ranging, desert-adapted taxa [2–7]. These studies often associated major genetic divergences with mountain-building events that took place in the late Neogene. As a result of these late Neogene events, deeply divergent clades were found to be restricted to the eastern (Chihuahuan) and western (Mojave and Sonoran) deserts. While the various hypotheses detailing the causes of the diversification of the Nearctic’s arid-adapted biota approach a generalized model [8], little work has been done on wide-ranging, arid-adapted arthropods [7]. Phylogeographic analyses of these organisms will aid in the development of a generalized model detailing diversification in the deserts. In addition to the importance of phylogeographic analyses to historical biogeography, these analyses often uncover the existence of cryptic species [9–13]. Recognition of these complexes is an essential aspect of documenting biodiversity and can be beneficial in the development of conservation strategies [14, 15]. While some phylogeographic investigations have been done on arid-adapted arthropods, like beetles [16, 17], velvet ants [7, 18], and spiders [2, 19], several diverse arthropod groups remain unexplored. One such group are the antlions (Neuroptera: Myrmeleontidae). Antlions in the tribe
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