Interspecific variation in defensive flower closure of Drosera (Droseraceae) is related to the herbivory pressure

Abstract Rapid plant movements in response to mechanical stimulation have long captivated mainstream interest. The flowers of Drosera species, notably studied for their defensive closure upon touch, protect their ovules from the specialist herbivore caterpillar Buckleria paludum. Although several species within Drosera exhibit variation in the speed of flower closure, the evolutionary and ecological contexts of these differences remain unclear. We hypothesize that the interspecific variation in flower closure speed has evolved in response to differing levels of herbivory pressure. Using Drosera rotundifolia and Drosera tokaiensis, we investigated the relationships between flower closure speed, effectiveness in ovule defence, herbivory pressure in nature, and the potential cost of flower closure. Our results indicate that D. tokaiensis, which exhibits faster flower closure than D. rotundifolia, more effectively reduces ovule damage due to B. paludum feeding attempts. Field surveys revealed that D. tokaiensis experiences higher herbivory pressure, likely due to its preference for drier microhabitats, which may influence the evolution of its rapid closure response. These findings enhance our understanding of the ecological and evolutionary factors driving the diversification of rapid plant movements and contribute to the emerging field of plant behavioural ecology.