Genetics of sprouting: effects of long-term persistence in fire-prone ecosystems

Fire functional traits (postfire resprouting and seeding) are considered to be adaptations for persisting in fire-prone environments. Although ecological and evolutionary consequences of sprouting have been extensively discussed, within-species genetic variability and structure are unknown. Here we report levels and distribution patterns of genetic polymorphisms in postfire stands of the predominant sprouter Nothofagus antarctica. Fresh foliage of 50 individuals was collected following a spatially explicit sampling design for isozyme analysis from two replicates of each of four habitat types inhabited by the species in northwestern Patagonia, Argentina: matorral, high elevation, forest, and temporally flooded basins. Average polymorphism per population ranged from 440% to 78% and mean gene diversity per site H-S varied from 0.187 to 0.274. These results show that sprouter populations hold considerable genetic variation. Significant genetic structure over short distances (< 50 m) was found at all locations. Ancient fine-scale genetic structure is preserved by occasional seedling establishment that results in high co-ancestry coefficients. Sprouter populations growing in suboptimal habitats such as matorral, high elevation or basins consist of pairs of heterozygous genets that occur at larger spatial scales as a result of micro-environmental heterogeneity and/or local competition between near neighbour genotypes. In contrast, homozygous pairs of individuals for distinct isozyme loci occurred at larger spatial scales in forest stands. This indicates that biparental inbreeding due to local propagule establishment may take place to some extent in sprouters growing under favourable conditions. Our results show that sprouters follow a long-lasting genet persistence strategy which most probably is selected under unpredictable disturbance regimes, such as fire.