AOBPreview originally published online on October 15, 2008
Annals of Botany 2008 102(6):1031-1041; doi:10.1093/aob/mcn195
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Limitations to Reproductive Output and Genetic Rescue in Populations of the Rare Shrub Grevillea repens (Proteaceae)
1 Centre for Environmental Stress and Adaptation Research (CESAR), Department of Genetics, Bio21 Institute, University of Melbourne, 30 Flemington Rd, Parkville, VIC 3010, Australia
2 School of Botany, University of Melbourne, Parkville, VIC 3010, Australia
3 Royal Botanic Gardens Melbourne, Private Bag 2000, South Yarra, VIC 3141, Australia
* For correspondence. E-mail gdholmes{at}unimelb.edu.au
Received: 8 July 2008 Returned for revision: 1 August 2008 Accepted: 28 August 2008 Published electronically: 15 October 2008
Background and Aims: When conserving rare plant species, managers are often faced with small and/or isolated populations displaying low levels of sexual reproduction and genetic variation. One option for reinvigorating these populations is the introduction of genetic material from other sites, but in some cases fitness may be reduced as a result of outbreeding depression. Here the pollination biology of the rare shrub Grevillea repens is studied across its natural range and reproductive responses following cross-pollination among populations are examined to determine factors that may be limiting sexual reproduction and the potential for genetic rescue.
Methods: Pollen manipulation treatments (self-, autogamous self-, cross- and open pollination) were applied to flowers to examine the breeding system and fruit and seed production in five populations of G. repens. Pollen production, presentation and viability were investigated and interpopulation crosses of increasing genetic distance performed among the populations.
Key Results: The study species is self-incompatible and displayed very low natural seed set over two seasons, due partly to low pollen viability in one of the populations. Within-population crossing increased fruit and seed production at some sites, indicating pollinator limitation. Interpopulation crosses further increased reproductive output in one population, suggesting mate limitation, and for this site there was a positive relationship between genetic distance among populations and the size of genetic rescue benefits. However, in other populations there was a decrease in fruit and seed set with increasing genetic distance.
Conclusions: The results highlight that management strategies involving interpopulation crosses can improve reproductive output in small, isolated populations of rare plants, but guidelines need to be developed on a population by population basis.
Key words: Grevillea repens, Proteaceae, genetic rescue, pollination ecology, self-incompatibility, breeding system, interpopulation cross, outbreeding depression, pollinator limitation, mate limitation, resource limitation
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