Abstract
Long‐lived, widespread plant species are expected to be genetically diverse, reflecting the interaction between large population sizes, overlapping generations, and gene flow. Such species are thought to be resilient to disturbance, but may carry an extinction debt due to reproductive failure. Genetic studies of Australian arid zone plant species suggest an unusually high frequency of asexuality, polyploidy, or both. A preliminary AFLP genetic study implied that the naturally fragmented arid zone tree, Acacia carneorum, is almost entirely dependent on asexual reproduction through suckering, and stands may have lacked genetic diversity and interconnection even prior to the onset of European pastoralism. Here we surveyed microsatellite genetic variation in 20 stands to test for variation in life histories and further assessed the conservation status of the species by comparing genetic diversity within protected stands in National Parks and disturbed range lands. Using herbarium records, we estimate that 219 stands are extant, all of which occur in the arid zone, west of the Darling River in southeastern Australia. With two exceptions, all surveyed stands comprised only one multilocus genet and at least eight were putatively polyploid. Although some stands comprise thousands of stems, our findings imply that the species as a whole may represent ~240 distinct genetic individuals, many of which are polyploid, and most are separated by >10 km of unsuitable habitat. With only 34% of stands (and therefore genets) occurring within conservation reserves, A. carneorum may be at much greater risk of extinction than inferred from on‐ground census data. Land managers should prioritize on‐ground preservation of the genotypes within existing reserves, protecting both vegetative suckers and seedlings from herbivory. Importantly, three stands are known to set viable seed and should be used to generate genetically diverse germ‐plasm for ex situ conservation, population augmentation, or translocation.
Highlights
Remnant stands of long-lived, recently abundant, and widespread plant species, in particular, temperate, and tropical forest trees, are often found to display high levels of genetic diversity, reflecting genetic interconnection, mediated by pollen or seed dispersal (Kramer, Ison, Ashley, & Howe, 2008) within typically large populations
Our findings of almost exclusively asexual reproduction and apparent variation in ploidy in A. carneorum stand in contrast to the initial finding of O’Brien et al (2014) of moderate clonality, with multiple genotypes detected within a smaller number of samples and surveyed stands
Our study revealed that the majority of surveyed stands comprise only one genetic individual
Summary
Remnant stands of long-lived, recently abundant, and widespread plant species, in particular, temperate, and tropical forest trees, are often found to display high levels of genetic diversity, reflecting genetic interconnection, mediated by pollen or seed dispersal (Kramer, Ison, Ashley, & Howe, 2008) within typically large populations. Such species may carry an extinction debt (Janzen, 1986). We use these data to expand knowledge of the distribution of genetic diversity within this species and to make recommendations for its conservation and management
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