Evaluating the Central-Marginal Hypothesis: Introgression and Genetic Variation at the Trailing Edge of Quercus...

Area of Science:

• Evolutionary Biology
• Population Genetics
• Conservation Genetics

Background:

• The central-marginal hypothesis (CMH) predicts lower genetic diversity at range edges.
• Deviations can occur due to hybridization, a common process in the genus Quercus.
• Understanding genetic patterns in range-edge populations is crucial for conservation.

Purpose of the Study:

• To investigate genetic diversity, structure, and introgression in Quercus bicolor across its distribution.
• To test the predictions of the CMH in a widespread eastern North American oak species.
• To assess the role of hybridization in shaping genetic landscapes at range margins.

Main Methods:

• RADseq genotyping of 142 Quercus bicolor individuals from 12 range-edge and 9 range-core sites.
• Incorporation of reference data from six sympatric white oak species to detect introgression.
• Ecological niche modeling (hindcast, current, forecast) to predict hybridization potential.

Main Results:

• Extensive introgression from Quercus lyrata was detected in southern range-edge populations, but not in core populations.
• Range-edge populations exhibited increased genetic structure and differentiation, but not reduced diversity or increased inbreeding.
• Introgressed ancestry was positively correlated with heterozygosity and differentiation, suggesting a buffering effect against genetic erosion.

Conclusions:

• Findings provide mixed support for the CMH, highlighting the significant role of introgression at range margins.
• Hybridization may introduce novel alleles, potentially benefiting range-edge populations.
• Future climate change and niche overlap suggest increased hybridization potential, with implications for Quercus bicolor conservation.