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Transient hybridization, not homoploid hybrid speciation, between ancient and deeply divergent conifers


Worth, JRP and Larcombe, MJ and Sakaguchi, S and Marthick, JR and Bowman, DMJS and Ito, M and Jordan, GJ, Transient hybridization, not homoploid hybrid speciation, between ancient and deeply divergent conifers, American Journal of Botany, 103, (2) pp. 246-259. ISSN 0002-9122 (2016) [Refereed Article]

Copyright Statement

Copyright 2016 Botanical Society of America

DOI: doi:10.3732/ajb.1500433


Premise of the study: Homoploid hybrid speciation is receiving growing attention due the increasing recognition of its role in speciation. We investigate if individuals intermediate in morphology between the two species of the conifer genus Athrotaxis represent a homoploid hybrid species, A. laxifolia, or are spontaneous F1 hybrids.

Methods: A total of 1055 individuals of Athrotaxis cupressoides and A. selaginoides, morphologically intermediate individuals, and two putative hybrid swarms were sampled across the range of the genus and genotyped with 13 microsatellites. We used simulations to test the power of our data to identify the pure species, F1s, F2s, and backcross generations.

Key results: We found that Athrotaxis cupressoides and A. selaginoides are likely the most divergent congeneric conifers known, but the intermediates are F1 hybrids, sharing one allele each from A. cupressoides and A. selaginoides at six loci with completely species specific alleles. The hybrid swarms contain wide genetic variation with stronger affinities to the locally dominant species, A. selaginoides and A. selaginoides backcrosses outnumbering A. cupressoides backcrosses. In addition, we observed evidence for isolated advanced generation backcrosses within the range of the pure species.

Conclusions: We conclude that, even though they can be large and long-lived, Athrotaxis hybrid swarms are on a trajectory of decline and will eventually be reabsorbed by the parental species. However, this process may take millennia and fossil evidence suggests that such events have occurred repeatedly since the early Quaternary. Given this timeline, our study highlights the many obstacles to homoploid hybrid speciation.

Item Details

Item Type:Refereed Article
Keywords:ancient conifer, Athrotaxis, homoploid hybrid speciation, hybrid swarm genesis/decline, pollen donor, spontaneous F1
Research Division:Biological Sciences
Research Group:Evolutionary biology
Research Field:Evolutionary biology not elsewhere classified
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the environmental sciences
UTAS Author:Larcombe, MJ (Mr Matthew Larcombe)
UTAS Author:Marthick, JR (Mr James Marthick)
UTAS Author:Bowman, DMJS (Professor David Bowman)
UTAS Author:Jordan, GJ (Professor Greg Jordan)
ID Code:106787
Year Published:2016
Funding Support:Australian Research Council (DP120100501)
Web of Science® Times Cited:13
Deposited By:Plant Science
Deposited On:2016-02-20
Last Modified:2017-11-03

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