The role of fire and a long‐lived soil seed bank in maintaining persistence, genetic diversity and connectivity in a fire‐prone landscape

Abstract

Aim Terrestrial plant ecology and evolution is significantly influenced by the phenomenon of fire, but studies of its potential impact on intraspecific genetic variation and phylogeography are rare. This understanding will be important for predicting the biogeographical consequences of changing fire regimes under global climate change. Here, we asked whether changing historical fire regimes, together with climatic and geological history, have influenced phylogeographical patterns in a fire‐ephemeral vine. We also asked whether demographic stochasticity associated with a fire‐ephemeral life history results in nuclear genetic drift as expected from spatio‐temporal patchiness, or if this effect is buffered by the connectivity and diversity afforded by a persistent soil seed bank. Location The fire‐prone, mediterranean‐type climate region of south‐western Australia. Methods We used Bayesian phylogeny reconstruction and statistical tests of demographic expansion based on variation at three non‐coding chloroplast sequence regions ( atpF, ndhF–rpl32, psbD–trnT ) to reconstruct phylogeographical history. Nuclear diversity and population structure at 11 microsatellite loci were investigated for evidence of genetic drift. Results Evidence for prolonged persistence and a lack of vicariance within the species range was found, together with strong evidence of historical demographic expansion. Contrary to expectations, there was little evidence of nuclear genetic drift despite strong, above‐ground spatio‐temporal population patchiness. Main conclusions Our findings suggest that a late Pleistocene increase in fire frequency may have led to demographic expansion in this fire‐ephemeral species; alternatively, the expansion signal may be an inherent feature of fire ephemerals with a persistent soil seed bank. Prolonged climatic stability has likely fostered persistence within the species range in contrast to contraction and vicariance. The notable lack of genetic drift implies a role for ample pollen dispersal and a long‐lived soil seed bank in the maintenance of diversity and connectivity in an otherwise stochastic, fire‐driven system.

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