Increased fire frequency promotes stronger spatial genetic structure and natural selection at regional and local scales in Pinus halepensis Mill.
The recurrence of wildfires is predicted to increase due to global climate change, resulting in severe impacts on biodiversity and ecosystem functioning. Recurrent fires can drive plant adaptation and reduce genetic diversity; however, the underlying population genetic processes have not been studied in detail. In this study, the neutral and adaptive evolutionary effects of contrasting fire regimes were examined in the keystone tree species Pinus halepensis Mill. (Aleppo pine), a fire-adapted conifer. The genetic diversity, demographic history and spatial genetic structure were assessed at local (within-population) and regional scales for populations exposed to different crown fire frequencies.



Eight natural P. halepensis stands were sampled in the east of the Iberian Peninsula, five of them in a region exposed to frequent crown fires (HiFi) and three of them in an adjacent region with a low frequency of crown fires (LoFi). Samples were genotyped at nine neutral simple sequence repeats (SSRs) and at 251 single nucleotide polymorphisms (SNPs) from coding regions, some of them potentially important for fire adaptation.



Fire regime had no effects on genetic diversity or demographic history. Three high-differentiation outlier SNPs were identified between HiFi and LoFi stands, suggesting fire-related selection at the regional scale. At the local scale, fine-scale spatial genetic structure (SGS) was overall weak as expected for a wind-pollinated and wind-dispersed tree species. HiFi stands displayed a stronger SGS than LoFi stands at SNPs, which probably reflected the simultaneous post-fire recruitment of co-dispersed related seeds. SNPs with exceptionally strong SGS, a proxy for microenvironmental selection, were only reliably identified under the HiFi regime.



An increasing fire frequency as predicted due to global change can promote increased SGS with stronger family structures and alter natural selection in P. halepensis and in plants with similar life history traits.
INIA Forest Research Centre, Department of Forest Ecology and Genetics, Carretera A Coruña km 7·5, 28040 Madrid, Spain.|INRA, Université de Bordeaux, UMR 1202 BIOGECO, 33610 Cestas, France.
Katharina B
KB
Budde
INIA Forest Research Centre, Department of Forest Ecology and Genetics, Carretera A Coruña km 7·5, 28040 Madrid, Spain.|INRA, Université de Bordeaux, UMR 1202 BIOGECO, 33610 Cestas, France.
Santiago C
SC
González-Martínez
INRA, UMR1062 CBGP, 34988 Montferrier-sur-Lez, France.
Miguel
M
Navascués
INRA, UMR 1334 AGAP, 34060 Montpellier, France.
Concetta
C
Burgarella
Faculty of Science and Technology, Free University of Bolzano, piazza Università 1, 39100 Bolzano, Italy.
Elena
E
Mosca
INIA Forest Research Centre, Department of Forest Ecology and Genetics, Carretera A Coruña km 7·5, 28040 Madrid, Spain.
Zaida
Z
Lorenzo
INIA Forest Research Centre, Department of Forest Ecology and Genetics, Carretera A Coruña km 7·5, 28040 Madrid, Spain.
Mario
M
Zabal-Aguirre
National Research Council, Institute of Biosciences and Bioresources, Via Madonna del Piano 10, 50019 Sesto Fiorentino (Florence), Italy.
Giovanni G
GG
Vendramin
Centro de Investigaciones sobre Desertificación (CIDE-CSIC), 46113 Moncada (Valencia), Spain.
Miguel
M
Verdú
Centro de Investigaciones sobre Desertificación (CIDE-CSIC), 46113 Moncada (Valencia), Spain.
Juli G
JG
Pausas
INIA Forest Research Centre, Department of Forest Ecology and Genetics, Carretera A Coruña km 7·5, 28040 Madrid, Spain.|INRA, Université de Bordeaux, UMR 1202 BIOGECO, 33610 Cestas, France.
Myriam
M
Heuertz
D057231:Climate Change; D005390:Fires; D014644:Genetic Variation; D018895:Microsatellite Repeats; D028223:Pinus / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D012641:Selection, Genetic; D013030:Spain; D014197:Trees / Q000235:genetics
Genetic diversity; demographic history; fire ecology; natural selection; spatial genetic structure