Parallel evolution of invasive ant populations
Alexander Mikheyev, Alexander (Sasha) Mikheyev
Research School of Biology, Australian National University, Australia & Ecology and Evolution Unit, Okinawa Institute of Science and Technology, Japan; Research School of Biology, Australian National University; Ecology and Evolution Unit, Australia & Okinawa Institute of Science and Technology, Japan
Species often encounter novel environments, which force them to adapt or potentially face extinction. Invasive species provide an excellent model system for the study of adaptation, since they by definition find themselves in non-native habitats and thrive. We studied the nature of adaptation in the little fire ant (Wasmannia auropunctata), which is one of the world’s most widespread and destructive invasive species. It is particularly suitable because of its unusual reproductive system, where males and females reproduce clonally, through androgenesis and thelytokous parthenogenesis, respectively, though other clonal sexually produced are occasionally progeny. Many, if not most, little fire ant invasions are initiated by the introduction of a single clonal couple, which can be found in the population decades after the initial introduction, competing with their sexually produced clonal offspring. At least two populations, in New Caledonia and in Gabon were started by the same queen clone (although mated to different males), allowing us to track the evolutionary changes that happen in the population over time. Using temporally structured sampling, we found that the frequency of the founding queen clone decreased over time, possibly because the sexually produced offspring were higher fitness. Surprisingly, the direction of genetic frequency changes from the founding clone to those that replace it were strongly correlated across the two populations, suggesting widespread genome-wide parallelism. These findings suggest that evolutionary responses can follow similar routes, even in drastically different environments, such as the Pacific islands, and mainland rainforest.