Genomic Data Support the Elevation of the Federally Listed El Segundo Blue (Euphilotes bernardino/Battoides allyni) to Species Status

The El Segundo Blue, Euphilotes battoides allyni (also listed as Euphilotes bernardino allyni), was described in the genus Shijimiaeoides as part of the battoides species group by Shields (1975). Both the genus and species group assignments in Euphilotes have undergone repeated revisions and reassignments (e.g., Pelham 2008, Pratt and Emmel 1998) and debate is active about which taxa merit species status or belong to which species in each of the three groups (E. rita, E. battoides and E. enoptes). Even the species assignment for the El Segundo Blue, perhaps one of the most intensively studied butterflies in the United States, is divided between E. battoides allyni (Pratt and Emmel 1998, Scott 1986, USFWS 2008) and E. bernardino allyni (Mattoni et al. 2001, Shields and Reveal 1988). All Euphilotes rely entirely on Buckwheats (Eriogonum, Polygonaceae), feeding on the inflorescences as larvae, and nectaring on the flowers as adults. Often, when different species of Euphilotes are sympatric, each relies on a single, different, species of Eriogonum, even when several buckwheat species are present in an area. Thus, a combination of morphological, phenological and hostplant data are often needed to separate species in the genus (Opler and Wright 1999). Because of its unique ecology and limited habitat on coastal sand dunes in southern California, the El Segundo Blue (ESB) was one of the first insects listed under the Endangered Species Act in 1976, only a few months after the first insect listed, Schaus’ Swallowtail (Heraclides aristodemus ponceanus). ESB has been the subject of intensive ecological studies and reintroduction efforts (Mattoni 1992, Mattoni et al. 2000, 2001), but has remained precariously limited in its range. In 2004, a morphologically similar population was discovered on coastal sand dunes, whose larvae also feed on Eriogonum parvifolum, over 150 miles to the north at Vandenberg Air Force Base (VAFB) in Santa Barbara County. This population was assigned to E. battoides allyni based on ecology and mitochondrial DNA haplotype information (Pratt and Stouthamer 2008). If this were actually E. b. allyni, it would have constituted a substantial extension to its known range and suggested a much more secure future for the species, being present on protected dunes on VAFB. Dupuis et al. (2020) conducted a genomic study of Euphilotes populations on multiple species of Eriogonum across southern California encompassing the new VAFB populations, ESB from all populations and other E. bernardino/ battoides populations from Santa Barbara through San Diego counties, including butterflies from coastal, inland desert and montane habitats. Their results not only demonstrated that ESB was not closely related to the populations at VAFB, but also that they were highly divergent from all surrounding E. bernardino / battoides populations (Fig. 1). The original subspecific description of E. b. allyni notes that two male E. battoides from Cedros Island, Baja California, Mexico also “fit the description” of allyni (Shields, 1975), so convergence of characteristics within isolated coastal populations, as seen at VAFB, was not unprecedented. As Figure 1 demonstrates, E. bernardino populations from areas of Los Angeles County that are adjacent to ESB coastal dune and bluff habitats are more closely related to other E. bernardino populations in the mountains and valleys of Los Angeles, San Bernardino, Riverside, and San Diego counties than they are to ESB (Dupuis et al. 2020). These levels of divergence across the genome in Dupuis et al. (2020) were not reflected at the same levels in mtDNA (COI haplotype diversity between populations ranged from 0–0.907, and Tajima’s D was negative for most populations), suggesting potential problems with relying on just mtDNA for conservation purposes and indicating that ESB is a unique species that has long been isolated and diverged from surrounding Euphilotes populations. We therefore elevate E. bernardino / battoides allyni to full species status as Euphilotes allyni. Type specimens continue to be held at the McGuire Center, University of Florida (holotype pictured in Figure 1).