Phylogenomic Evidence of Fire Regime Changes: The Case of a Resprouting Juniper

The onset of the Mediterranean climate, with its characteristic seasonal droughts and increased fire activity, marked a significant shift in the evolution of Mediterranean flora. One trait to adapt to this fire regime shift is the ability to resprout from a lignotuber. We used genotyping-by-sequencing (GBS) data to estimate the origin of lignotuber resprouting in the Iberian Juniperus oxycedrus complex and the period when fires-and the Mediterranean seasonality-became sufficiently frequent and stable to favour such plant adaptations. We then infer the demographic consequences of possessing this trait. Results indicate that resprouting and non-resprouting lineages diverged around 6.23 Ma, aligning with key aridification events (e.g., the Messinian Salinity Crisis) followed by the establishment of the Mediterranean climate. We propose that fire-adaptive traits, such as lignotuber resprouting, can serve as proxies to estimate fire regime shifts; by doing so, we provide new insights into the assembly of the Mediterranean biome.