Female heterogamety and speciation: Reduced introgression of the Z chromosome between two species of nightingales
Abstract
The X chromosome plays a large role in intrinsic postzygotic isolation. The role of the Z chromosome in speciation is much less understood.
To explore the role of the Z chromosome in reproductive isolation, we studied nucleotide variation in two closely related bird species, the Thrush Nightingale (Luscinia luscinia) and the Common Nightingale (L. megarhynchos). Our results suggest that the nightingale species diverged approximately 1.8 Mya.
We found strong evidence of gene flow after divergence in both directions, although more introgression occurred from L. megarhynchos into L. luscinia. Gene flow was significantly higher on the autosomes than on the Z chromosome.
Our results support the idea that the Z chromosome plays an important role in reproductive isolation in birds.