El Segundo Blue is a full species

One of my side projects in grad school was to analyze data on the endangered El Segundo Blue that had been collected by Dr. Rudi Mattoni at the Los Angeles International Airport dunes. It eventually ended up as a bit larger collaboration with Dr. Cor Zonneveld from the Netherlands (Mattoni et al. 2001) and ended up setting me on the road to working on butterfly monitoring over the last couple of decades. The range of the species was then thought to be restricted to the dunes along the Santa Monica Bay from Venice, give or take, to the bluffs and up onto the northern part of the Palos Verdes Peninsula. It has been, since 1975, classified as a subspecies of the Square-spotted Blue (Euphilotes bernardino), which some authorities call Euphilotes battoides. The bernardino/battoides status had little practical effect, since it was protected by the Endangered Species Act and distinct enough not to be confused within its known range.

Things got a little funny when a population of butterflies looking a whole lot like El Segundo Blue was discovered at Vandenberg Air Force Base on the central California coast. Some preliminary genetics work was done and it was proclaimed to be El Segundo Blue (Pratt & Stouthamer 2008). I had my doubts, which I kept mostly, but not completely, to myself, since I didn’t see how such a disjunct distribution could have developed with no evidence of the butterfly at any location in between, notwithstanding the presence of its foodplant.

The US Fish and Wildlife Service eventually decided to sort out this question and wisely awarded funding to Dr. Dan Rubinoff at the University of Hawaii to do a more detailed genomic study of the Vandenberg butterfly, El Segundo Blue, and an array of surrounding populations of Euphilotes bernardino. Dan and his grad students had sorted out the phylogenetics of a listed California moth species (Rubinoff et al. 2015), so they were the right team for the job. I helped out where I could with the El Segundo Blue study, with recommendations on sampling locations.

The results of the showed quite clearly that the Vandenberg AFB butterfly was not El Segundo Blue, but was much more closely related to other nearby populations of Euphilotes bernardino (Dupuis et al. 2020). It is even more closely related to Square-spotted Blues in San Diego County than to El Segundo Blue. The visual similarity with El Segundo Blue arises therefore from convergence — adaptation to a similar environmental condition along the coast. When El Segundo Blue itself was described (Euphilotes bernardino allyni), Shields (1975) noted that there was an island population from Baja California that looked similar (but was not included in the subspecies, presumably because of the great distance separating it from the Santa Monica Bay). The research by Dupuis et al. (2020) also revealed that El Segundo Blue differed considerably from all of the other Euphilotes bernardino populations. Its level of difference suggested a separate and distinct evolutionary path from the other populations. Interestingly, it showed that the northern Palos Verdes Peninsula population of El Segundo Blue — up on the bluffs rather than on the dune system — shared a little bit of genetic similarity with a population in northeast San Pedro (green on the graphic below). Years ago, we used to call that bluff population E. bernardino X, because it was like El Segundo Blue, but just a little bit different. The genetics showed that to be the case, but still similar enough to cluster in with El Segundo Blue.

Based on this genetic information, we have now elevated El Segundo Blue to full species status as Euphilotes allyni (Rubinoff et al. 2021). This change has no practical effect on its protection — it was and remains protected by the Endangered Species Act — but it does reinforce the importance of conserving this unique branch of the evolutionary tree associated with the dunes and bluffs of the Santa Monica Bay. We have put a whole lot of work into recovering El Segundo blue, including advocacy to keep LAX from trying to expand across the El Segundo Dunes and out into the ocean (thanks to the late Senator Tom Hayden and an early morning press conference on top of the dunes for killing that idea), the Beach Bluffs Restoration Project, restorations at Torrance Beach, Ballona Wetlands, and the Ballona Lagoon (successful until bulldozed by a misguided restoration contractor). Work continues today coordinated by the ESB Coalition and includes even more restoration projects in the works that will further expand the occupied range of this beautiful species.

References

Dupuis, J. R., S. M. Geib, K. H. Osborne, and D. Rubinoff. 2020. Genomics confirms surprising ecological divergence and isolation in an endangered butterfly. Biodiversity and Conservation 29:1897–1921.

Mattoni, R., T. Longcore, C. Zonneveld, and V. Novotny. 2001. Analysis of transect counts to monitor population size in endangered insects: the case of the El Segundo Blue butterfly, Euphilotes bernardino allyni. Journal of Insect Conservation 5:197–206.

Pratt, G. F. & R. Stouthamer. 2008. The genetic relationships between the El Segundo Blues from Los Angeles County and Santa Barbara County. Report. University of California at Riverside, Riverside.

Rubinoff, D., M. San Jose, P. Johnson, R. Wells, K. Osborne, and J. J. Le Roux. 2015. Ghosts of glaciers and the disjunct distribution of a threatened California moth (Euproserpinus euterpe). Biological Conservation 184:278–289.

Rubinoff, D., T. Longcore, J. R. Dupuis, and K. H. Osborne. 2021. Genomic data support the elevation of the federally isted El Segundo blue (Euphilotes bernardino/battoides allyni) to species status. Journal of the Lepidopterists’ Society 75(2):161-164.

Shields, O., 1975. Studies on North American Philotes (Lycaenidae). IV. Taxonomic and biological notes, and new subspecies. Bulletin of the Allyn Museum 28:1–36.

Travis Longcore, Ph.D.
June 18, 2021