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Expansion of the rare Eucalyptus risdonii under climate change through hybridization with a closely related species despite hybrid inferiority

Pfeilsticker, TR, Jones, RC ORCID: 0000-0002-6491-1423, Steane, DA ORCID: 0000-0002-8061-8454, Harrison, PA ORCID: 0000-0002-3502-0242, Vaillancourt, RE ORCID: 0000-0002-1159-9149 and Potts, BM ORCID: 0000-0001-6244-289X 2021 , 'Expansion of the rare Eucalyptus risdonii under climate change through hybridization with a closely related species despite hybrid inferiority' , Annals of Botany, vol. 129, no. 1 , pp. 1-14 , doi:

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Background and AimsHybridization is increasingly recognized as an integral part of the dynamics of species range expansion and contraction. Thus, it is important to understand the reproductive barriers between co-occurring species. Extending previous studies that argued that the rare Eucalyptus risdonii was expanding into the range of the surrounding E. amygdalina by both seed and pollen dispersal, we here investigate the long-term fitness of both species and their hybrids and whether expansion is continuing.MethodsWe assessed the survival of phenotypes representing a continuum between the two pure species in a natural hybrid swarm after 29 years, along with seedling recruitment. The performance of pure species as well as of artificial and natural hybrids was also assessed over 28 years in a common garden trial.Key ResultsIn the hybrid zone, E. amygdalina adults showed greater mortality than E. risdonii, and the current seedling cohort is still dominated by E. risdonii phenotypes. Morphologically intermediate individuals appeared to be the least fit. Similar results were observed after growing artificial first-generation and natural hybrids alongside pure species families in a common garden trial. Here, the survival, reproduction, health and growth of the intermediate hybrids were significantly less than those of either pure species, consistent with hybrid inferiority, although this did not manifest until later reproductive ages. Among the variable progeny of natural intermediate hybrids, the most E. risdonii-like phenotypes were the most fit.Key ConclusionsThis study contributes to the increasing number of reports of hybrid inferiority in Eucalyptus, suggesting that post-zygotic barriers contribute to the maintenance of species integrity even between closely related species. However, with fitness rapidly recovered following backcrossing, it is argued that hybridization can still be an important evolutionary process, in the present case appearing to contribute to the range expansion of the rare E. risdonii in response to climate change.

Item Type: Article
Authors/Creators:Pfeilsticker, TR and Jones, RC and Steane, DA and Harrison, PA and Vaillancourt, RE and Potts, BM
Keywords: Eucalyptus amygdalina, Eucalyptus risdonii, hybridization, hybrid swarm, hybrid zone, post-zygotic barriers, fitness, outbreeding depression, hybrid inferiority
Journal or Publication Title: Annals of Botany
Publisher: Oxford Univ Press
ISSN: 0305-7364
DOI / ID Number:
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Copyright 2021 The Author(s)

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