Journal Article

Window of opportunity: an episode of recruitment in a <i>Banksia</i> hybrid zone demonstrates continuing hybridization and phenotypic plasticity

A. V. Usher, R. J. Whelan and D. J. Ayre

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 105, issue 3, pages 419-429
Published in print March 2010 | ISSN: 0305-7364
Published online February 2010 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcq001
Window of opportunity: an episode of recruitment in a Banksia hybrid zone demonstrates continuing hybridization and phenotypic plasticity

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

In perennial plants (especially post-fire resprouters), extant populations may reflect recruitment events in the distant past. This is true of hybrid zones formed by two Banksia species of swamps and woodlands in south-eastern Australia, Banksia robur and B. oblongifolia. Both resprout after fire but recruitment is dependent on periodic fires. Although plants of intermediate morphology have also been identified as hybrids using allozyme markers, the extent of ongoing hybridization is unknown. This study investigates whether both microsatellite markers and morphological measurements can be used to distinguish between the two species and their hybrids. A recent recruitment event and microsatellite markers allow the frequency of ongoing hybridization to be estimated, and also the effects of environmental variation on the morphology of plants and seedlings to be tested.

Methods

Variation at seven microsatellite loci was scored and seven leaf characteristics within putatively pure stands and mixed stands of both species were measured, revealing that the two species were genetically and morphologically distinct and that mixed stands also contained genetically and sometimes morphologically distinct hybrids. An opportunity created by wildfires was used to analyse the genetics and morphometrics of adults and seedlings from two hybrid zones.

Key Results

Approximately 9 % of adults and 21 % of seedlings were identified as genetic hybrids in both hybrid zones. Within these sites, the genotype of mature plants correlated well with morphology, except for some hybrid plants that had parental morphology. However, seedling morphology was highly variable and insufficient to describe the composition of the hybrid zone in this cohort. Greater phenotypic plasticity was evident among seedlings growing within the hybrid zones than seedlings growing in pots.

Conclusions

The hybrid zones are complex and the range of genotypes detected in seedlings reveals both continuing hybridization and introgression.

Keywords: Banksia oblongifolia; Banksia robur; genotype; hybrid; morphology; phenotypic plasticity; plant; recruitment; seedling

Journal Article.  5881 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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