Plant species with larger extrafloral nectaries produce better quality nectar when needed and interact with the best ant partners

Abstract

Few studies have explored the phenotypic plasticity of nectar production on plant attractiveness to ants. Here, we investigate the role of EFN size on the productivity of extrafloral nectar in three sympatric legume species. We hypothesised that plant species with larger EFNs i) have higher induced nectar secretion after herbivory events, and ii) are more likely to interact with more protective, i.e., dominant, ant partners. We target 90 plants of three Chamaecrista species in the field. We estimated EFN size and conducted field experiments to evaluate any differences in nectar traits before and after leaf damage to investigate the phenotypic plasticity of nectar production across species. We censused ant species feeding on EFNs over time. Plant species increased nectar descriptors after leaf damage, but in different ways. Supporting our hypothesis, C. duckeana, with the largest EFN size, increased all nectar descriptors, with most intense post-herbivory induced response, taking its place as the most attractive to ants, including dominant species. EFN size variation was an excellent indicator of nectar productivity across species. The higher control over reward production in plants with larger-sized EFNs reflects an induction mechanism under damage that reduces costs and increases the potential benefits of indirect biotic defences.

Age-dependent miR156-targetedSPLsare required for extrafloral nectary development inPassifloraspp

“…4), which might make them less attractive to ants. In addition, the quality of the nectar is impacted by the size of EFNs in different species, and affects ant visitation (Alencar et al, 2023). We therefore evaluated nectar availability and carbohydrate content in the EFNs from miR156-OE and NT plants.…”

“…It is important to note that the lower sucrose content might be associated with lower expression of SUC2-like transporters in miR156-OE leaf primordia as, during the nectar secretion phase of wild type EFNs, genes encoding sucrose transporter are up-regulated (Chatt et al, 2021). Nectar with high concentrations of sugars seems to be more attractive to ants than those with low concentrations, resulting in increased visitation and persistence of the protective agent on the plant (Villamil et al, 2013;Alencar et al, 2023).…”

“…Changes in nectary size and abundance may partially explain the indifferent behavior of ants towards miR156-OE plants. Species with abundant, more prominent and accessible EFNs attract more ants than those with smaller nectaries, increasing defense performance (Apple & Feener, 2001;Alencar et al, 2023). Removing EFNs reduces ant patrolling, but mechanically damaging EFNs without affecting nectar supply has not been shown to limit ant visitation (Izarigue et al, 2013).…”

“…Removing EFNs reduces ant patrolling, but mechanically damaging EFNs without affecting nectar supply has not been shown to limit ant visitation (Izarigue et al, 2013). Other variables, such as nectar quality and quantity, interfere with plant-animal mutualistic interactions (Heil et al, 2011;Alencar et al, 2023). The altered sugar profile in miR156-OE EFNs may have contributed to the observed reduction in ant patrolling.…”