Demographic model of admixture predicts symmetric introgression when a species expands into the range of another: A comment on Currat et al. (2008)

Da-Yong ZHANG

State Key Laboratory of Earth Surface Processes and Resource Ecology and Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Beijing Normal University, Beijing 100875, China.

Abstract: A recent model by Currat et al. indicates that when one species colonizes an area already occupied by a closely related species, massive introgression of neutral genes should take place primarily in the direction from the local to the invasive species. Here, I show that this model relies on an assumption that might not capture the true dynamics of how species exchange migrants during admixture. As an alternative, I formulate a new model, based on a different and perhaps more biologically realistic assumption of interbreeding, that demonstrates symmetric introgression as compared to the large and asymmetric introgression predicted by the original model. The new model indicates that asymmetry is not a default property of introgressions, thus necessitating alternative explanations for the common observation of massive asymmetric introgression including sex-biased dispersal.

Keywords: hybridization; introgression; neutral model; organelle capture; range expansion.