Aggressive bodyguards are not always the best: Preferential interaction with more aggressive ant species reduces reproductive success of plant bearing extrafloral nectaries

Abstract

Variation in partner species and frequency of interaction between species pairs are potential drivers of the net outcome of generalized mutualisms. In ant-plant mutualisms, the quality of defence provided by ants is related to ant aggressiveness. Hence, we hypothesize that the performance of plants bearing extrafloral nectaries will be higher when they interact more frequently with more aggressive ant species. We estimated ant aggressiveness in the field by observing their behaviour towards soil baits. Afterwards, we observed the frequency with which individuals from these ant species visited plants through an entire reproductive cycle. We measured the production and persistence of plants reproductive structures through this period and the total seed production. Increasing in the interaction frequency with highly aggressive ants reduced the number of floral buds and seeds produced. Increased visitation frequency by less aggressive ants increased the number of floral buds and seeds per branch. The inverse relationship between ant aggressiveness and seed production may be influenced by the costs imposed by different mutualistic partners. Thus, frequent interaction with highly aggressive ants may lead to a higher accumulation of costs through time, resulting in a negative net outcome for the plants. Our results bring new evidence highlighting the importance to incorporate temporal aspects in the study of mutualistic interactions. We suggests that the quality of mutualistic partners must be understood as a function of its per-interaction benefit and their cumulative costs to their partner over time, what puts in check our current classification regarding partner quality in mutualistic systems.

Nectar quality affects ant aggressiveness and biotic defense provided to plants

“…We hypothesize that plants should secrete higher‐quality nectar in situations in which they might most benefit from better protection (Smith, Lanza, & Smith, ). Since extrafloral nectar secretion follows optimal defense theory (Holland, Chamberlain, & Horn, ) and highly aggressive ants may tilt the balance to a negative outcome for plants, as highly aggressive ants tend to exclude also pollinators from the plant (Melati & Leal, ), natural selection should favor secretion of enriched nectar in situations in which the benefits provided by ants surpass the costs, such as when herbivore pressure is high (Millán‐Cañongo, Orona‐Tamayo, & Heil, ).…”

Untitled

“…As our results suggest that a more balanced and nutritious nectar with amino acids, although being more expensive to the plants, improves ant defense behavior, plants should secrete a valuable nectar in situations in which they might benefit from better protection (Smith et al 1990). As extrafloral nectar secretion follows optimal defense theory (Holland et al 2009) and highly aggressive ants may tilt the balance to a negative outcome for plants (Melati & Leal 2018), natural selection should favor secretion of enriched nectar in situations in which the benefits provided by ants surpass the costs, as periods when herbivore pressure is higher (Millán-Cañongo et al 2014).…”

Variation in the production of plant tissues bearing extrafloral nectaries explains temporal patterns of ant attendance in Amazonian understorey plants

“…This association has the potential to intensify biotic defence on young tissues that are preferred by herbivores (Coley, 1980), even though the herbivory pressure is likely to be slightly lower in the dry season (Aide, 1988;Coley & Barone, 1996;Wolda, 1988). In such interactions, dominant ant species recruit more workers to plants (Cerdá, Arnan, & Retana, 2013), which could impose high costs to the plant partner except when plants are under high herbivore pressure (Melati & Leal, 2018). Therefore, the role of such association over time should be interpreted with caution, mainly because the direction and magnitude of ant effect on plant fitness depend on herbivore pressure.…”