Authors: Berggren, Åsa; Kanuch, Peter;Cassel-Lundhagen, Anna;Preuss, Sonja;Nordlander, Göran;

To understand colonization success of an invasive species we need to know the origin of the founders, where and when they were introduced, and spread from introduction site(s). Admixture of different genetic lineages from multiple introductions is generally hypothesized to be beneficial thanks to adaptive variation and heterozygosity-fitness correlations. In this study, population genetic and landscape data was gathered for Roesel’s bush-cricket currently expanding its range in Europe. We examined how colonization history and landscape structure affect its spread and population genetic structure. Using ecological and dispersal information with genetic structure inferred from 29 locations, we found that two parapatric founding lineages coexist with very little gene flow. Our findings are in strong contrast to the hypothesis that different genetic lineages will admix when introduced to the same area. The presence of separate lineages decades after introduction and without physical barriers shows some mechanism prevents admixture. Lineages with different genetic setups may have adapted independently to local conditions and their admixture result in loss of locally adapted genotypes and less viable hybrids. Our data indicate that human transportation of agricultural goods may play an important role for the spatial genetic pattern of the species by aiding the spread.