Conservation Genetics and Genomics of the Narrowly Endemic Island Marble Butterfly Euchloe ausonides insulanus

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The island marble butterfly (Euchloe ausonides insulanus) was first discovered on Vancouver Island, Canada in 1861.  Based on morphological characteristics, it has been described as a subspecies of Euchloe ausonides.  After a collection was made in 1908 on Gabriola Island, Canada, the island marble was not seen again until 1998 on San Juan Island, Washington, USA. Recent surveys have determined that the island marble now exists only at San Juan Island National Historical Park in the American Camp Unit and on adjoining lands on San Juan Island. The island marble is currently a candidate for listing as an endangered species.

The US Fish and Wildlife Service (USFWS), National Park Service (NPS), along with other cooperators have implemented multiple ongoing preservation and habitat restoration activities/initiatives to protect remnant populations of the island marble butterfly. However, no detailed information exists on levels of genetic diversity, population sub-structuring, or relatedness among island marble butterfly individuals. In 2017, the USGS Leetown Science Center partnered with the USFWS to initiate a genetic study of the island marble butterfly to help guide recovery and restoration efforts. 

To facilitate a genetic investigation of the remnant island marble population, USFWS has provided multiple non-lethally collected samples of island marble butterfly tissue from the captive rearing program for genetic analysis at the Leetown Science Center. These samples consist of larval natural mortalities, larval manure pellets (frass) from individual known larvae, residual cellular fluid from eclosed exuviae, and whole dried exuviae. These samples have been collected over 2016, 2017, and 2018 representing multiple year-classes.

Through shotgun genomic DNA sequencing of an exuviae sample at LSC, a suite of 14 microsatellite loci were developed for genotyping the DNA extracted from these different tissue types. These microsatellite loci are being used to generate multi-locus genotypes of island marble butterfly samples to determine levels of neutral genetic diversity, relatedness, inbreeding, and population structure.  In addition, high throughput sequencing of multiple samples is being undertaken for a comparison of mitochondrial genomes among the island marble and closely related species.

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An island marble butterfly Euchloe ausonides insulanus caterpillar.

(Credit: Gary Tarleton, USFWS. Public domain.)

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Jenny Shrum (National Park Service) checks on island marble butterfly Euchloe ausonides insulanus pupae in the captive rearing facility at San Juan Island National Park, Washington, USA.

(Credit: Karen Reagan, USFWS. Public domain.)

Adult island marble butterfly

An adult island marble butterfly Euchloe ausonides insulanus resting on vegetation in San Juan Island National Park, Washington, USA.

(Credit: Karen Reagan, USFWS. Public domain.)