Relative frequency of sympatric species influences rates of interspecific hybridization, seed production and seedling performance in the uncommon Eucalyptus aggregata
Article first published online: 10 SEP 2008
© 2008 The Authors. Journal compilation © 2008 British Ecological Society
Journal of Ecology
Volume 96, Issue 6, pages 1198–1210, November 2008
How to Cite
Field, D. L., Ayre, D. J., Whelan, R. J. and Young, A. G. (2008), Relative frequency of sympatric species influences rates of interspecific hybridization, seed production and seedling performance in the uncommon Eucalyptus aggregata. Journal of Ecology, 96: 1198–1210. doi: 10.1111/j.1365-2745.2008.01434.x
- Issue published online: 15 OCT 2008
- Article first published online: 10 SEP 2008
- Received 30 January 2008; accepted 30 July 2008; Handling Editor: John Pannell
- genetic diversity;
- genetic swamping;
- habitat fragmentation;
- inbreeding depression;
- pollen swamping;
- population size
- 1Habitat fragmentation can alter the relative frequency of cross-compatible species within an area, which can affect the levels of interspecific hybrid production and reduce the viability of small populations through genetic and demographic swamping. For 18 populations of Eucalyptus aggregata, we examined the effects of absolute and relative population size (compared with its congeners E. rubida, E. viminalis and E. dalrympleana) on hybrid production, genetic diversity and subsequent seed production and seedling performance.
- 2Relative population size was strongly negatively correlated with rates of hybrid seed production, suggesting increased hybridization when the potential sources of interspecific pollen outnumber the sources of intraspecific pollen for E. aggregata trees.
- 3Genetic diversity was negatively correlated with relative population size which suggests that hybridization may maintain diversity lost through bottlenecks and drift following reductions in population size. However, the presence of fertile hybrid adults, and introgressed leaf traits within populations exhibiting high hybridization rates, suggests that small E. aggregata populations may be vulnerable to genetic swamping by common congeners.
- 4Amongst an array of population parameters (population sizes, genetic diversity and inbreeding), seed production was only positively correlated with relative population size, whereby sites with low relative population sizes tended to produce fewer seed. This could be due to the action of pre-zygotic barriers which removes inviable hybrid genotypes as levels of interspecific pollen flow increase.
- 5Germination and survivorship displayed a similar positive correlation with relative population size, suggesting post-zygotic hybrid breakdown may also contribute towards to demographic swamping of remnant populations.
- 6Synthesis. Our results suggest that relative population size is an important parameter determining rates of hybrid production, seed production and seedling performance. Furthermore, relative population size has stronger effects on population fecundity than absolute population size, genetic diversity and levels of inbreeding. Relative population sizes > 0.5 (i.e. at least equal frequencies of parentals) may be required to avoid the deleterious effects of genetic and demographic swamping on the viability of rare species.