How does the post-fire facultative seeding strategy impact genetic variation and phylogeographical history? The case of Bossiaea ornata (Fabaceae) in a fire-prone, mediterranean-climate ecosystem

Aim Fire regimes are a significant driver of plant adaptation and evolution, and projected changes under a changing climate will have significant implications for demographic and evolutionary responses of plant populations in fireprone regions globally. We tested predictions regarding level and pattern of genetic variation within a model post-fire facultative seeder, Bossiaea ornata (Fabaceae), that exhibits a combination of both post-fire resprouting and seeding strategies. Location Fire-prone forests in the mediterranean-climate region of southwestern Australia. Methods We genotyped individuals with eight microsatellite markers and four non-coding chloroplast sequence regions to assess population genetic variation and reconstruct phylogeographical history. Results Extremely high levels of chloroplast (H-D = 0.95) and nuclear (H-E = 0.81) diversity were detected. Nuclear population differentiation was weak (F-ST = 0.06) and chloroplast phylogeographical structure was absent. A significant excess of rare chloroplast haplotypes was detected (D, F-S, R-2; all P < 0.01), consistent with demographic expansion. Main conclusions Results suggest that a facultative seeding life-history affords the benefits of both obligate resprouting and obligate seeding strategies in terms of resistance and resilience to fire. High diversity and low differentiation are likely driven by long generational overlap (resprouter feature), regular post-fire population supplementation from a persistent soil seed bank (seeder feature) and longterm stability. Expansion signals may be a feature of species with regular, synchronous post-fire recruitment from a soil seed bank, rather than evidence of a single range or demographic expansion event, as typically interpreted. The facultative seeding strategy may therefore offer resilience to potential increases in fire frequency under a changing climate in fire-prone regions.