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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 and Jones, RC and Steane, DA and Harrison, PA and Vaillancourt, RE and Potts, BM, Expansion of the rare Eucalyptus risdonii under climate change through hybridization with a closely related species despite hybrid inferiority, Annals of Botany, 129, (1) pp. 1-14. ISSN 0305-7364 (2021) [Refereed Article]

Copyright Statement

Copyright 2021 The Author(s)

DOI: doi:10.1093/aob/mcab103


Background and Aims

Hybridization 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.


We 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 Results

In 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 Conclusions

This 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 Details

Item Type:Refereed Article
Keywords:Eucalyptus amygdalina, Eucalyptus risdonii, hybridization, hybrid swarm, hybrid zone, post-zygotic barriers, fitness, outbreeding depression, hybrid inferiority
Research Division:Biological Sciences
Research Group:Evolutionary biology
Research Field:Biological adaptation
Objective Division:Plant Production and Plant Primary Products
Objective Group:Forestry
Objective Field:Native forests
UTAS Author:Pfeilsticker, TR (Ms Thais Ribeiro Pfeilsticker)
UTAS Author:Jones, RC (Dr Rebecca Jones)
UTAS Author:Steane, DA (Dr Dorothy Steane)
UTAS Author:Harrison, PA (Dr Peter Harrison)
UTAS Author:Vaillancourt, RE (Professor Rene Vaillancourt)
UTAS Author:Potts, BM (Professor Brad Potts)
ID Code:148355
Year Published:2021
Funding Support:Australian Research Council (DP0664923)
Web of Science® Times Cited:3
Deposited By:Plant Science
Deposited On:2022-01-02
Last Modified:2022-05-04

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