Using museum specimens to assess historical distribution and genetic diversity in an endangered butterfly

Abstract

The Miami blue butterfly,Cyclargus thomasi bethunebakeri, is a state-endangered taxon in Florida and a candidate for federal listing. This once common butterfly saw a dramatic decline in population number and abundance in the 1970s and 1980s, but significant collections of individuals prior to this decline are deposited in natural history museums. Using museum specimens, we quantified the genetic diversity in a historical population present in Key Largo, Florida in 1940, 1960, and 1980. Genetic diversity was consistently high within this historical population, but diversity was observed to decrease over the decades sampled. A comparison of historical diversity from the Key Largo population with the extant populations on Bahia Honda State Park (BHSP) and Key West National Wildlife Refuge (KWNWR) revealed differences in allelic frequencies, but only minor differences in the overall number of alleles. The historical distribution of butterflies throughout the Florida Keys further suggests a metapopulation structure. This structure involved partially-isolated populations ofC. t. bethunebakerithat were loosely connected via gene flow and that underwent localized extinction and colonization events along the chain of suitable habitat in the Florida Keys. It appears that a “mini-metapopulation” currently exists on BHSP and KWNWR; structures that are similar to the historical metapopulation structure and distribution of populations on a larger scale. Knowledge of historical distribution helps to plan future reintroduction events with captive-bred butterflies. Additional populations of butterflies may represent undiscovered genetic diversity that, if appropriate, may be further incorporated into captive-breeding efforts.