Molecular and morphological evidence of natural interspecific hybridization between the uncommon Eucalyptus aggregata and the widespread E. rubida and E. viminalis |
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Authors: | David L Field David J Ayre Rob J Whelan Andrew G Young |
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Institution: | (1) Department of Ecology and Evolutionary Biology, 25 Willcocks street, Toronto, ON, Canada, M5S 3B2;(2) School of Biological Sciences, Institute for Conservation Biology, University of Wollongong, Wollongong, NSW, 2522, Australia;(3) CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia |
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Abstract: | Human activities can promote increased hybridization in the genus Eucalyptus with potentially detrimental consequences for the persistence of rare species. However, many hybrid combinations have not
been investigated with combined use of genetic markers and morphology. We assessed the efficiency of the STRUCTURE program
and morphological intermediacy for identifying hybrids between the uncommon tree, Eucalyptus aggregata, which putatively hybridizes with the common congeners, E. rubida and E. viminalis in south-eastern Australia. We sampled 1,005 seedlings across 27 populations, all seedlings were genotyped at 6 allozyme
loci and scored for 22 stem and leaf characters. Both marker sets confirmed that E. aggregata is hybridizing with both E. rubida and E. viminalis. Allozymes revealed hybrids from E. aggregata trees in 88% of populations and hybrids comprised 7.3% of all seedlings. Both genetics and morphology indicated that ~50%
were likely to be F1 hybrids, and both simulations and morphological characteristics indicated that the remainder were mostly backcrosses. Morphological
analysis correctly distinguished 71% of F1 hybrids from parentals and was least accurate when dealing with potential backcrosses (50% success). Hence, techniques using
genetic data (no prior information) and the assessment of appropriate admixture thresholds through simulations provided the
most accurate estimates of hybrid frequency. In this study, potential introgression and the high frequency of hybrids in small
populations (~30%), suggests that hybridization should be considered in the management and conservation of E. aggregata. |
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Keywords: | Conservation genetics Hybridization Population size Eucalyptus Habitat fragmentation |
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