Do Hybrid Trees Inherit Invasive Characteristics? Fruits of Corymbia torelliana X C. citriodora Hybrids and Potential for Seed Dispersal by Bees

PLOS ONE, Dec 2019

Tree invasions have substantial impacts on biodiversity and ecosystem functioning, and trees that are dispersed by animals are more likely to become invasive. In addition, hybridisation between plants is well documented as a source of new weeds, as hybrids gain new characteristics that allow them to become invasive. Corymbia torelliana is an invasive tree with an unusual animal dispersal mechanism: seed dispersal by stingless bees, that hybridizes readily with other species. We examined hybrids between C. torelliana and C. citriodora subsp. citriodora to determine whether hybrids have inherited the seed dispersal characteristics of C. torelliana that allow bee dispersal. Some hybrid fruits displayed the characteristic hollowness, resin production and resin chemistry associated with seed dispersal by bees. However, we did not observe bees foraging on any hybrid fruits until they had been damaged. We conclude that C. torelliana and C. citriodora subsp. citriodora hybrids can inherit some fruit characters that are associated with dispersal by bees, but we did not find a hybrid with the complete set of characters that would enable bee dispersal. However, around 20,000 hybrids have been planted in Australia, and ongoing monitoring is necessary to identify any hybrids that may become invasive.

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Do Hybrid Trees Inherit Invasive Characteristics? Fruits of Corymbia torelliana X C. citriodora Hybrids and Potential for Seed Dispersal by Bees

September Do Hybrid Trees Inherit Invasive Characteristics? Fruits of Corymbia torelliana X C. citriodora Hybrids and Potential for Seed Dispersal by Bees Helen Margaret Wallace 0 1 2 Sara Diana Leonhardt 0 1 2 0 1 Genecology Research Centre, Faculty of Science , Health , Education and Engineering, University of the Sunshine Coast , Maroochydore DC 4558 , Australia , 2 Department of Animal Ecology and Tropical Biology, University of Würzburg , 97074, Würzburg , Germany 1 Funding: This work was funded in part by an Australian Research Council Linkage Grant LP0218877 to HMW and the Queensland Government Smart State Program via the Smart Forests Alliance Queensland to HMW. Funding for SDL was provided by the Deutsche Forschungs- Gemeinschaft (DFG project: LE 2750/1-1) and by a grant of the German Excellence Initiative to the Graduate School of Life Science, University of Würzburg. The funders had no role in study design 2 Editor: Sergio R. Roiloa, University of A Coruña , SPAIN Tree invasions have substantial impacts on biodiversity and ecosystem functioning, and trees that are dispersed by animals are more likely to become invasive. In addition, hybridisation between plants is well documented as a source of new weeds, as hybrids gain new characteristics that allow them to become invasive. Corymbia torelliana is an invasive tree with an unusual animal dispersal mechanism: seed dispersal by stingless bees, that hybridizes readily with other species. We examined hybrids between C. torelliana and C. citriodora subsp. citriodora to determine whether hybrids have inherited the seed dispersal characteristics of C. torelliana that allow bee dispersal. Some hybrid fruits displayed the characteristic hollowness, resin production and resin chemistry associated with seed dispersal by bees. However, we did not observe bees foraging on any hybrid fruits until they had been damaged. We conclude that C. torelliana and C. citriodora subsp. citriodora hybrids can inherit some fruit characters that are associated with dispersal by bees, but we did not find a hybrid with the complete set of characters that would enable bee dispersal. However, around 20,000 hybrids have been planted in Australia, and ongoing monitoring is necessary to identify any hybrids that may become invasive. - Introduction Global interest in invasive trees is increasing and invasive trees have recently been recognized as having substantial impacts on biodiversity and ecosystem functioning [1]. There are many factors that may contribute to trees becoming invasive, and some critical factors include tree dispersal mechanisms, hybridisation and escape from plantations. Tree species dispersed by animals are disproportionality more likely to become invasive and long-distance seed dispersal, often a feature of animal dispersal, can play a crucial role in invasions [2, 3]. Invasion may also be facilitated by hybridisation [4]. Hybridisation is an important evolutionary process for plants that allows them to evolve rapidly and can confer new characteristics that enable plants data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. to proliferate, persist and invade [5]. Hybridisation between domesticated plants and wild relatives is well documented as a source of new weeds [4, 6]. Lastly, tree invasions are often driven by tree species escaping from cultivation or plantations [7]. Thus management strategies for tree plantations need to account for the possibility of seed dispersal into surrounding areas and subsequent invasions [7]. Corymbia torelliana is an invasive tree species with an unusual animal dispersal mechanism [8, 9]. The tree is dispersed by stingless bees foraging for resin inside the fruit [8–11]. Stingless bees collect plant resins for nest building and defence [12, 13]. Seeds taken up by resin collecting bees may be dispersed long distances (over 300 m), and the tree is invasive in areas outside of its natural range where it co-occurs with stingless bees [8, 10]. C. torelliana is the only Corymbia species to be dispersed by bees and to be invasive. Other members of the genus are not invasive and are dispersed very short distances through barochory. Furthermore C. torelliana is invasive only in areas where it co-occurs with stingless bees [8, 10]. This suggests that this unique dispersal mechanism contributes greatly to making C. torelliana invasive. Moreover, C. torelliana (section Cadagaria) hybridizes readily with three closely related species in the spotted gum group, (section Politaria) Corymbia citriodora subsp. citriodora, C. citriodora subsp. variegata, C. henryi and C. maculata [14–17]. In addition, C. torelliana is able to form hybrids with more distantly related Corymbia species [15]. Corymbia species and their hybrids are of increasing interest for forestry plantations globally due to their fast growth and resistance t (...truncated)


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Helen Margaret Wallace, Sara Diana Leonhardt. Do Hybrid Trees Inherit Invasive Characteristics? Fruits of Corymbia torelliana X C. citriodora Hybrids and Potential for Seed Dispersal by Bees, PLOS ONE, 2015, Volume 10, Issue 9, DOI: 10.1371/journal.pone.0138868