Assessment of the invasion potential of two genetically distinct populations of the Ponto-Caspian amphipod - Dikerogammarus villosus

Abstract

This PhD thesis explored intraspecific variation in invasive potential in freshwater ecosystems using an invasive Ponto-Caspian amphipod – Dikerogammarus villosus – as a model species. This species has spread in Europe from two genetically distinct and geographically isolated populations: the Danube and the Dnieper deltas, forming the Western and the Eastern invasive groups, respectively. Its wide distribution and high invasiveness make it an ideal model for studying invasion potential at a population level. Firstly, I tested whether the Eastern Group could invade lakes using boating as a vector. Analyses revealed that tourism, especially sailing, facilitated its spread in the Masurian Lakeland. This species rapidly colonized new environments, displacing native and invasive species. Next, I assessed morphological variation across populations. The Eastern Group showed morphological adaptations for herbivory, while the Western Group exhibited adaptations for enhanced predatory capacity and locomotion. Morphospace changes indicated high phenotypic plasticity in the Eastern Group. Analyses of food preferences confirmed the conclusions of the morphological analyses - the Western Group being more carnivorous may pose a greater threat to aquatic macroinvertebrates, while the Eastern Group being more omnivorous may use food resources more efficiently in limited conditions. Finally, I compared dispersal abilities. The Eastern Group successfully competed for preferred habitats, forcing the Western Group to disperse further. These dynamics suggest that the Western Group may spread more widely in future. This research highlights how genetic and environmental factors shape invasive traits, emphasizing the need to study multiple populations to predict invasive species’ spread and ecological impacts.