Low genetic differentiation despite fragmentation in an endangered fire-sensitive shrub
International Journal of Plant Sciences
Premise of research. Worldwide, fire-sensitive shrubs have an important but underresearched life history, and in Australia they are threatened by anthropogenic changes to fire regimes and habitat loss. Typically, adults are killed by fire, but they can also senesce and die if interfire intervals are prolonged. Populations can regenerate from seed banks displaying fire-stimulated germination; however, populations are ephemeral, and true population sizes and connectedness are difficult to estimate. Persoonia hirsuta ssp. evoluta is an endangered, inconspicuous, fire-sensitive shrub with a soil-stored seed bank currently known only from a small number of locations within the fire-prone Sydney Basin. Although it appears highly fragmented and populations are typically small, we predicted that its seed bank would buffer populations against loss of genetic diversity and population differentiation. Methodology. We used microsatellite markers to assess genetic variation within three aboveground populations of P. hirsuta separated by up to 25 km. The largest and most isolated population, at Appin, New South Wales, Australia, occurs on a mine site and may be subject to disturbance. We compared levels of genetic diversity and estimated the mating systems and genetic connectedness of plants within the three sites. Pivotal results. As predicted, all populations displayed similar genetic diversity, as judged by expected heterozygosity and allelic richness, and displayed little differentiation. All populations appear predominantly outcrossed. However, STRUCTURE and principal coordinates analyses showed that Appin individuals were distinct from those at the other locations. Conclusions. Our data imply that even for fire-sensitive species with few aboveground populations, genetic diversity can be maintained by the buffering effect of persistent seed banks with diversity reflecting historically greater interpopulation gene flow. While all P. hirsuta sites support comparable genetic diversity, the preservation of known populations is critical. Conservation efforts should include searches for additional populations, fire-stimulated germination of seed banks, and collection of seed for propagation in a nursery or direct sowing.
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