@article {147, title = {Fine-scale environmental control of hybridization in oaks}, journal = {Molecular EcologyMolecular Ecology}, year = {2012}, pages = {n/a-n/a}, abstract = {Natural hybridization is attracting much interest in modern speciation and conservation biology studies, but the underlying mechanisms remain poorly understood. In particular, it is unclear why environmental changes often increase hybridization rates. To study this question, we surveyed mating events in a mixed oak stand and developed a spatially explicit individual-based hybridization model. This model, where hybridization is frequency-dependent, pollen is nonlimiting and which allows immigrant pollen to compete with local pollen, takes into account species-specific pollen dispersal and sexual barriers to hybridization. The consequences of pollen limitation on hybridization were studied using another simple model. The results indicate that environmental changes could increase hybridization rates through two distinct mechanisms. First, by disrupting the spatial organization of communities, they should decrease the proportion of conspecific pollen available for mating, thus increasing hybridization rates. Second, by decreasing the density of conspecifics, they should increase pollen limitation and thus hybridization rates, as a consequence of chance pollination predominating over deterministic pollen competition. Altogether, our results point to a need for considering hybridization events at the appropriate level of organization and provide new insights into why hybridization rates generally increase in disturbed environments.}, keywords = {disturbance, immigration, mass action model, paternity analysis, pollen limitation, Quercus petraea, Quercus robur}, isbn = {1365-294X}, author = {Lagache, L{\'e}lia and Klein, Etienne K. and Guichoux, Erwan and Petit, R{\'e}my J.} } @article {131, title = {Exploring Species Limits in Two Closely Related Chinese Oaks}, journal = {PLoS ONEPLoS ONE}, volume = {5}, number = {11}, year = {2010}, pages = {e15529}, publisher = {Public Library of Science}, abstract = {Background

The species status of two closely related Chinese oaks, Quercus liaotungensis and Q. mongolica, has been called into question. The objective of this study was to investigate the species status and to estimate the degree of introgression between the two taxa using different approaches.

Methodology/Principal Findings

Using SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa. Bayesian clusters, principal coordinate analysis and population genetic distance trees all classified the oaks into two main groups consistent with the morphological differentiation of the two taxa rather than with geographic locations using both types of markers. Nevertheless, a few individuals in Northeast China and many individuals in North China have hybrid ancestry according to Bayesian assignment. One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific FST simulation analysis, suggesting a role for divergent selection in differentiating species.

Main Conclusions/Significance

All results based on SSRs and AFLPs reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry. They should therefore be considered as discrete taxonomic units. Yet, the degree of introgression varies between the two species in different contact zones, which might be caused by different population history or by local environmental factors.

}, author = {Zeng, Yan-Fei and Liao, Wan-Jin and Petit, R{\'e}my J. and Zhang, Da-Yong} }