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Promiscuous Proteaceae: natural hybridisation between Australian native Lomatia species
Natural hybridisation occurs when individuals from two natural populations, distinguishable on the basis of one or more heritable characters, are able to reproduce successfully. Hybridisation can introduce variation and novel traits into populations and can offer a platform for adaptive evolution and speciation.
This study provides the first molecular confirmation of hybridisation events between the Australian native species Lomatia myricoides (Gaertner f.) Domin and L. silaifolia (Smith) R.Br. (Proteaceae). Morphologically intermediate, putative L. myricoides x silaifolia hybrids had previously been found in eastern Australia where the species’ ranges overlap. A combination of genetic (twelve nuclear microsatellites), morphometric and ecological approaches were adopted to characterise patterns of hybridisation at three locations; the Royal National Park, Bobbin Head National Park and Newnes State Forest.
One population consisted of pure species with no evidence of current hybridisation; another included a small number of early generation hybrid individuals (F1s and F2s), while the third was a hybrid swarm, formed by extensive introgression and admixture of genotypes.
Interestingly, leaf shape and plant size functioned as strong visual clues of hybridization events in the field, as morphologically intermediate plants were genetically confirmed to be hybrids. Hybrids were also fertile and their flowering produced seeds with germination rates comparable to parental species, suggesting hybridisation will be ongoing in this system.
Thus, hybridisation between L. myricoides and L. silaifolia is confirmed however the processes vary dynamically within the region of overlapping species distributions. These results have also highlighted the importance of gene flow through hybridization as a powerful means of generating molecular and morphological diversity within existing plant lineages.