Ant guards can increase plant fitness by deterring herbivores but may also reduce it by interfering with pollination, hence ant-plant interactions are ideal systems in which to study costs and benefits of mutualisms. While ant impacts on herbivory are well-studied, much less is known about impacts on pollinators and associated consequences for plant mating systems and fitness. We used field experiments to quantify the effect of ant guards on pollinator community composition, frequency and duration of flower visits, and cascading effects on plant mating system and plant fitness in Turnera velutina (Passifloraceae). Although ant patrolling did not affect pollinator community composition or visitation frequency, it decreased pollinator foraging time and flower visit duration. Such behavioural changes resulted in reduced pollen deposition on stigmas, decreasing male fitness whilst increasing outcrossing rates. This study contributes to understanding how non-pollinators, such as these defensive mutualists, can shape plant mating systems.

Ant guards influence the mating system of their plant hosts by altering pollinator behaviour