Impacts of human-induced environmental disturbances on hybridization between two ecologically differentiated Californian oak species.
Natural hybridization, which can be involved in local adaptation and in speciation processes, has been linked to different sources of anthropogenic disturbance. Here, we use genotypic data to study range-wide patterns of genetic admixture between the serpentine-soil specialist leather oak (Quercus durata) and the widespread Californian scrub oak (Quercus berberidifolia). First, we estimated hybridization rates and the direction of gene flow. Second, we tested the hypothesis that genetic admixture increases with different sources of environmental disturbance, namely anthropogenic destruction of natural habitats and wildfire frequency estimated from long-term records of fire occurrence. Our analyses indicate considerable rates of hybridization (> 25%), asymmetric gene flow from Q. durata into Q. berberidifolia, and a higher occurrence of hybrids in areas where both species live in close parapatry. In accordance with the environmental disturbance hypothesis, we found that genetic admixture increases with wildfire frequency, but we did not find a significant effect of other sources of human-induced habitat alteration (urbanization, land clearing for agriculture) or a suite of ecological factors (climate, elevation, soil type). Our findings highlight that wildfires constitute an important source of environmental disturbance, promoting hybridization between two ecologically well-differentiated native species.
Department of Integrative Ecology, Estación Biológica de Doñana, EBD-CSIC, Avda. Américo Vespucio s/n, E-41092, Seville, Spain.
Joaquín
J
Ortego
Appalachian Laboratory, University of Maryland Center for Environmental Science, 301 Braddock Road, Frostburg, MD, 21532, USA.
Paul F
PF
Gugger
Department of Ecology and Evolutionary Biology, University of California, Box 957239, Los Angeles, CA, 90095, USA.|Institute of the Environment and Sustainability, University of California, Box 951496, Los Angeles, CA, 90095-1496, USA.
Victoria L
VL
Sork
D001499:Bayes Theorem; D017753:Ecosystem; D051456:Gene Flow; D005843:Geography; D006802:Human Activities; D006801:Humans; D006824:Hybridization, Genetic; D016014:Linear Models; D008957:Models, Genetic; D025341:Principal Component Analysis; D029963:Quercus / Q000235:genetics*; D013045:Species Specificity

Quercus
; California; environmental disturbance; genetic admixture; genetic structure; hybridization; introgression; wildfire