Systematics Section / ASPT
Dodd, Richard S , Afzal-Rafii, Zara .
Landscape patterns of multiple hybrid structure in California red oaks.
The four western North American red oak species (Quercus wislizeni, Q. parvula, Q. agrifolia and Q. kelloggii) are known to produce hybrid products in all inter-specific combinations. However, it is unknown whether hybrids are transitory resulting from inter-specific gene flow, or whether they are maintained through extrinsic selection. Here, we examine cryptic hybrid structure in Quercus wislizeni through a broad region in northern California including zones of contact and isolation from three other western North American red oaks using AFLP molecular markers. All four species were simultaneously detected in the genetic background of individuals morphologically assigned to Q. wislizeni, although the contribution of Q. kelloggii was minor. In some cases, introgression was detected well outside the region of sympatry with one of the parental species. Molecular structure at the individual level indicated this was due to long distance pollen dispersal and not to local extinction of parental species. Species admixture proportions were correlated with climatic variables. Greater proportions of Q. agrifolia and Q. parvula were present in the genetic background of Q. wislizeni in sites with cooler and more humid summers, corresponding with habitat preferences of the parental species. Partial Mantel tests indicated that climate was more important than distance from pollen source in this association. Despite high levels of introgression, species integrity was maintained in some populations in close proximity to the other species, providing further support to environmental selection in determining population genetic structure. Thus, the contribution of species mixtures to population genetic structure varies across the landscape according to availability of pollen, but more importantly to varying environmental selection pressures that produce a complex pattern of hybrid and pure gene pools.
1 - University of California, Environmental Science Policy and Management, 151 Hilgard Hall, Berkeley, California, 94720, USA
2 - CNRS-Universite d'Aix-Marseille III, IMEP, Faculte des Sciences St Jerome, Marseille, 13397, France
Presentation Type: Paper
Location: Cottonwood A (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 4:45 PM