Hierarchical population genetic analysis reveals metapopulation structure in a phytophagous Galapagos beetle

The Galapagos Archipelago has long been considered a living laboratory for the study of evolution. Due to geographic isolation and speciation many end emic animal and plant groups have radiated on the islands. Although the ver tebrate fauna of these islands (e.g. giant tortoises, Darwin's finches) has been studied in great detail, little is known about invertebrates and espe cially insects. Results are given of a population genetic study on the phyt ophagous beetle Nesaecrepida darwini. This small alticine beetle is present on all major islands but shows a discontinuous population distribution. To obtain population genetic information we used cellulose acetate gel electr ophoresis to study allozyme variation in 6 populations from 3 islands. Twel ve presumptive loci, including 9 polymorphic ones, were analysed The result s show low heterozygosity values, with the lowest genetic diversity on the youngest island. F-statistics (mean F-ST = 0.431) indicate a very large amo unt of genetic differentiation between populations. Hierarchical analysis i ndicates little inter-island gene flow but also considerable genetic variat ion between populations occurring on the same island. These results strongl y suggest a metapopulation structure with recurrent extinctions and recolon isations of populations within each island. Recent field observations suppo rt these findings.