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Resurrection Ecology

Contrary to popular conservation aphorism, extinction may not always be forever. Occasionally, the thoughtful reintroduction of an organism closely related to an extinct type can result in the functional reconstruction of the animal or plant thought to be lost. Recently, in Britain, lepidopterists imported subspecies closely related to the extinct British Large Blue (Maculinea arion), bred them up in labs, and introduced the reconstructed species into its old habitat.

The conditions permitting such a Lazarus act are rare, and their em-ployment raises all sorts of philosophical questions. Still, reestablishment of near relatives in restored habitats may be an act worth considering. I feel the attempt would be worth it, if only for the vigorous debate and solid experience it would promote in the young practice I am bound to term "Resurrection Ecology."

I would like to nominate the Xerces Blue butterfly (Glaucopsyche xerces) as a candidate for such radical reconstitution. In 1875, San Francisco lepidopterist Herman Behr wrote to his Chicago colleague Herman Strecker, lamenting that the Xerces Blue was "now extinct, as regards the neighborhood of San Francisco. The locality where it used to be found is converted into building lots, and between German chickens and Irish hogs no insect can exist besides louse and flea." Eventually, Behr's prophecy panned out, and the Xerces Blue ceased flying altogether.

Often, when a taxon (a kind of plant or animal) becomes extinct, it leaves behind related taxa that might or might not have become separate species since their isolation from one another. The surviving taxon might be considered a different subspecies from the extinct type, or a different (but very close) species. Transported to the site of the extinction (assuming its supportive conditions have been restored), the survivor may reinoculate the place with organisms similar to those lost; and in time, under those conditions, may evolve traits that make them virtually indistinguishable from the original occupants. This has occurred in nature. For instance, extinct Floridian butterflies were replenished by arrivals from the Bahamas and Cuba.

The Endangered Species Act allows for the listing of subspecies, recognizing that these are the active units of evolution, where differentiation is in the process of occurring. Subspecies are where the action is, in evolutionary terms. So when a creature drops out due to environmental change, surviving related taxa in not-too-distant localities may contain much the same genetic complement as the lost ones.

Even after Behr's lament to Strecker about its decline, the Xerces Blue remained common in places. William Hovanitz, a prominent California lepidopterist, used to bicycle out to the Presidio and collect as many as he liked without making a dent in their numbers, as he worked out their life history. He spoke about the area with the Presidio commander, who left it undisturbed for the time. The renowned insect photographer Dr. Edward Ross and Harry Davis of UC Davis were the last entomologists to see Xerces Blues on the wing. They observed them around a blue-flowered lupine near the Marine Hospital above Lobos Creek, on a slope at the head of a natural amphitheater. That upland was subsequently flattened, graveled, and built upon by the Army's ordnance department. The last known Xerces Blues flew over dunes at the Presidio in 1943.

Now, an opportunity looms that could jump-start a whole new era of butterfly (and habitat) sensitivity and imagination. Three conditions have created this possibility. First, since Xerces' demise, the military reservation known as the Presidio, where the butterfly last flew, has become part of the Golden Gate National Recreation Area. Extensive wetland restoration is taking place on part of the Presidio along San Francisco Bay, including restoration of native San Francisco duneland habitat.

Second, the recovery of a Los Angeles cousin of the Xerces Blue, the Palos Verde Blue (Glaucopsyche lygdamus palosverdesensis) is underway. The Palos Verdes Blue was thought to be the first federally listed taxon to become extinct on the government's watch. But it was later rediscovered by lepidopterist Rudi Mattoni at a US Navy fuel depot. The Palos Verdes Blue has since become the target of a major lab-rearing and restoration effort by Dr. Mattoni, and the early results are promising.

Third, some fairly near relatives of Xerces may be extant today. Thomas C. and John F. Emmel describe a new Xerces-like subspecies of the Silvery Blue (Glaucopsyche lygdamus) from Santa Rosa Island, one of the California offshore islands and part of Channel Islands National Park. Although the males are a paler, more violet blue than those of G. xerces, and the females browner, the underside hindwings do bear prominent white halos around the black spots, and sometimes only the white spots as found in "the true Xerces of San Francisco." As the Emmels put it, the name they gave the new subspecies, G. l. pseudoxerces, "reflects its phenotypic similarity to the extinct Xerces Blue."

The discovery of an animal bearing a striking similarity and relationship to Xerces, contemporary with a vigorous attempt to restore suitable habitat in the last place Xerces existed, suggests a symbiotic opportunity too obvious and appealing to ignore.

"Resurrection" of Whom?

Some lepidopterists believe that the Xerces Blue was the same species as Silvery Blue. Whether this is the case or they are simply closely related, it is unlikely that the Silvery Blue and Xerces differentiated very long ago in the evolutionary past.

Closeness might be judged by food habits. The Emmels found the island Silvery Blue females ovipositing on California broom (or deerweed, Lotus scoparius), a legume that was the Xerces' primary, if not sole, caterpillar host plant in San Francisco. But some believe Xerces was not strictly a lotus eater. Tree lupine has been reported as a host for it, and the larvae consumed Nuttall's pea in the laboratory.

Nor was Xerces always white-spotted; there was both a form with small black irises and one with larger dark centers that resembled the Silvery Blue. It was just this extreme polymorphy that made Xerces so interesting from a population genetics standpoint. Though the new island subspecies is the closest in appearance to the usual form of the extinct Xerces, it might not be the most relevant factor in deciding whether the Santa Rosa Island form should serve as the best founder population for a reintroduction.

Maybe the founder population should be the closest geographically. A Silvery Blue population that had evolved closer to the San Francisco Peninsula might well prove more suitable for local conditions than one from southern California. And geographically closer Silveries might also be more recently related to Xerces than the Channel Islands population. Besides, it would likely prove much easier to obtain and transport living material from outside a national park than from within.

The likely candidate would be G. l. incognitus (formerly called G. l. behrii) from Marin County, Santa Clara, and elsewhere on the north and central California coast. Rudi Mattoni, to whom the idea of restoring Xerces occurred years ago, suggests that this subspecies could be laboratory-reared en masse and interbred to achieve something of the polymorphy of Xerces, while strengthening genetic variability. In order to further broaden the gene pool, founders should be drawn from several sites.

Regardless of the subspecies employed, there would be nothing to lose (except for a modest number of founder individuals who would die) by reintroducing blues to the Xerces' last habitat. There might be a great deal to gain in terms of expanded support for the restoration and refined management practice.

Reintroduction is a last resort that should never be undertaken until the original extinction is virtually certain, and this can be difficult to prove. Nonetheless, perhaps the Presidio restoration will succeed in bringing back a patch of habitat bearing some resemblance to the city's lost landscape. This patch could grow. If all went well, and if local conditions acted upon a similar genome to fix the white-spotted blue butterfly and attune it to the rebuilt habitat, who knows? At some future date, we might even be able to say: Xerces flies again!