Reproductive biology of the invasive Gleditsia triacanthos L. (Fabaceae)

Abstract

Biotic invasions constitute a threat for natural communities, affecting ecological and evolutionary integrity of natural ecosystems. Gleditsia triacanthos is an invasive species in many regions of the world. In Argentina, its populations are expanding over native vegetation of different ecoregions. The aim of this work is to study the reproductive biology of the invasive honey locust, characterizing the reproductive individuals, the assemblage of pollinators, the pollination process, the compatibility system, and the reproductive success. Considering that G. triacanthos could be characterized as a novel invader in Argentina and plant-pollinator interactions could be important to facilitate plant invasions, we expect to find (a) an assembly of generalist floral visitors that promote pollination; (b) that fruits and seeds could be produced through self- (autogamy) or cross-pollination (mediated by pollinators); (c) that pollinators can increase reproductive success of exposed flowers compared to those experimentally isolated from pollinators. The studied populations (Córdoba Province, central Argentina) can be characterized as polygamous andro-dioecious, with a higher proportion of male individuals. Although honeybees were the most frequent pollinator, all floral visitors could be potential pollinators and the honey locust can be characterized as pollinator-generalist. G. triacanthos produces fruits and seeds by spontaneous self-pollination, but a higher reproductive success was observed after hand cross- or natural pollinations. Producing both self- and cross-pollinated seeds could be advantageous for this species during different stages of the invasion process. The generalist pollination system presented by G. triacanthos, the high production of pollen by male individuals compared to the individuals with perfect flowers, and the higher fruit and seed set by cross- or natural pollinated flowers are all traits favouring the invasion process. These reproductive traits could be considered when designing management strategies to control the expansion of this invasive species.