Temporal Dynamics of Biological Invasions: Perception of Host Quality Differs Between Native and Alien Host Species

The spread of non-native species into new regions is a dynamic process driven by behavioural adaptations to local environments and species interactions. Interactions between coexisting populations can lead to localised coevolutionary patterns, shaped by the duration of their co-occurrence. We investigated the relationship between the European bitterling fish (<i>Rhodeus amarus</i>), a parasitic fish that lays eggs in the gills of unionid mussels, and an invasive mussel host, <i>Sinanodonta woodiana</i>, which has spread across Europe over the past 50 years. The bitterling, a host generalist, can parasitise any European unionid mussel species, but its reproductive success with <i>S. woodiana</i> is limited due to the mussel's ability to reject bitterling eggs. We tested three hypotheses on the role of rapid local coevolution in host choice using <i>S. woodiana</i> populations with recent (5 years), intermediate (17 years), and long-term (40+ years) associations with European bitterling. We experimentally evaluated the spawning preferences of four bitterling populations: three coexisting with their respective <i>S. woodiana</i> populations and one naïve to <i>S. woodiana</i>. All bitterling populations avoided <i>S. woodiana</i> from the most recently established population. Neither local coexistence nor individual mussel quality influenced bitterling responses to <i>S. woodiana</i>. In contrast, bitterling selected native <i>Anodonta anatina</i> mussels based on individual quality rather than population identity. These findings suggest that native species can recognise and avoid an invasive host at the invasion front, where co-occurrence is recent.