High levels of genetic variability and population differentiation in Gressittacantha terranova (Collembola, Hexapoda) from Victoria Land, Antarctica

Allozyme electrophoresis was used to assess genetic variability and differe ntiation in 22 populations of Gressittacantha terranova Wise (Hexapoda, Col lembola) from a coastal area of Victoria Land between the Mariner Glacier a nd the Nansen Ice Sheet. Allelic frequencies were determined at five enzyme loci: Phi, Pgm, Hk, Mpi and Mdh. Levels of variability, estimated as rates of heterozygosity, were higher than those calculated for the same loci in taxonomically related and non-related species of non-Antarctic Collembola. Thus, in spite of the ecological simplicity of Antarctic terrestrial ecosys tems, G. terranova is characterized by high levels of genetic variability, and the 22 populations could be divided into three geographic groups, separ ated by the Aviator and Campbell glaciers. Genetic differentiation reflects the geographic arrangement of the populations, suggesting that the glacier s are effective barriers to gene flow, and that the patchy distribution of collembolan species in Antarctica has the potential to induce, in the long term, microspeciation processes. Interestingly, detectable genetic differen tiation was observed between six populations collected at Edmonson Point, e ven though these are very close to each other, indicating the impact of geo graphic isolation even within short distances. The only exception to the co ngruence between genetic and geographic structuring was provided by the pop ulation of Apostrophe Island, for which a recent introduction with individu als coming from southern populations is suggested.