Uncovering transgenerational phenotypic variation in Parthenium hysterophorus populations in Israel

MAIN CONCLUSION: Invasive Parthenium hysterophorus achieves rapid colonization via phenological divergence and population-specific transgenerational plasticity, balancing maternal environmental effects with rigid developmental canalization to outperform native flora across diverse habitats. Parthenium hysterophorus L. is a highly aggressive invasive weed that has spread across more than 50 countries, causing severe agricultural, ecological, and public health problems. Understanding phenotypic variation among invasive populations is critical for predicting invasion dynamics and designing effective management strategies. This study investigated phenological variation and transgenerational plasticity among five P. hysterophorus populations in northern Israel over three years. We compared developmental traits (emergence, bolting, flowering, height, and biomass) between field-collected seeds and their progeny grown under controlled greenhouse conditions. Significant phenological differences were observed among the populations, with field populations exhibiting more uniform development. These disparities persisted through to final height and weight measurements. A detailed transgenerational analysis of two contrasting populations (Tirat Zvi and Ha'Hotrim) revealed population-specific patterns of developmental plasticity. The Tirat Zvi population, originating from an extremely arid environment and representing the earliest documented Israeli introduction, demonstrated significant transgenerational shifts in emergence timing and a 25% increase in biomass under controlled conditions, while maintaining conserved flowering timing. In contrast, the Ha'Hotrim population exhibited a limited transgenerational response, with significant changes only in bolting timing. These contrasting patterns suggest different adaptive strategies: environmental anticipation through maternal effects versus intrinsic developmental canalization. The pronounced phenological divergence among populations, despite their short geographic separation, supports the hypothesis of multiple independent introductions or rapid local adaptation, with important implications for managing this invasive species in diverse agricultural landscapes.