Reproductive strategies and reliance on pollinators in three highly invasive plant species

The plant-pollinator mutualistic relationship is fundamental to ecosystem functioning, as most angiosperms rely on animal vectors for reproductive success. However, many invasive plant species possess reproductive traits such as self-compatibility and apomixis that may reduce their dependence on pollinators. Understanding these reproductive strategies is important for explaining invasion success and planning effective management. Here, we investigated the reproductive strategies and seed production of three invasive plant species ( Ageratum conyzoides , Chromolaena odorata and Mikania micrantha ) using pollination exclusion experiments in the Eastern Himalaya biodiversity hotspot. Pollination experiments were conducted on 300 experimental twigs (100 per species) using four treatments: a control (open pollination) and three exclusion treatments employing open mesh, large mesh (~ 8 mm) and small mesh (~ 1 mm) bags that provided different levels of pollinator access. We quantified seed set (per floret) and seed mass across treatments. A. conyzoides and C. odorata exhibited no significant differences in seed set or seed mass across pollination treatments. In contrast, M. micrantha showed a significant reduction in seed set and seed mass in complete pollinator exclusion compared with the control. Furthermore, seed set and seed mass were positively correlated in M. micrantha , whereas no such relationship was detected in A. conyzoides or C. odorata . These findings suggest that reproductive independence from pollinators and autonomous reproductive flexibility contributes to the successful establishment of A. conyzoides and C. odorata in disturbed habitats, whereas M. micrantha relies more strongly on pollinator-mediated reproduction in combination with alternative strategies such as vegetative propagation for successful invasion.