Wild cucumber invasiveness: impact of seasonal changes on biometric seed traits and dispersal strategy

Wild cucumber (Echinocystis lobata) is an invasive annual vine rapidly spreading across Central European riparian zones. Its success is linked to seed dispersal, with hydrochory expected to play a major role, but the specific mechanisms are not fully understood. This study examines whether E. lobata uses a dual dispersal strategy by seed morphological differences and hydrodynamic behavior, supporting both short-distance and long-distance dispersal. Seeds were collected in autumn and early spring, and analysed for morphology, buoyancy, and hydrodynamic properties. Over 150 seeds underwent biometric measurements: digital image correlation for swelling deformation, micro-computed tomography for internal structure, and hydrodynamic properties. Approximately 23% of seeds were buoyant, with buoyant ones present in both autumn and spring seed groups. Buoyant seeds had larger surface areas and internal air cavities, contributing to lower drag and enhanced passive transport in water. Using digital image correlation and micro-computed tomography imaging, we visualized seed coat swelling patterns and quantified internal structures. Hydrodynamic experiments revealed that buoyant seeds experienced lower drag and slower acceleration. Under oscillatory flow, buoyant seeds exhibited passive propulsion at 1 Hz, indicating a resonance effect facilitating dispersal during fluctuating water flow. These findings support a dual dispersal strategy: temporal seed release and buoyancy enable both local recruitment and long-distance dispersal, likely contributing to invasive success in riparian habitats.