Adaptive introgression between two <i>Drosophila</i> species enhances heat tolerance despite barriers to gene flow

The useful part

Ritchie As global temperatures rise and heat waves become more frequent, populations must adapt rapidly to avoid local extinctions. However, certain genomic regions, containing barrier loci, may resist introgression. We experimentally tested whether strong heat stress selection can overcome such barriers and facilitate the transfer of adaptive alleles to improve heat tolerance.

How it works

• We also examined whether chromosomal inversions, which can tightly link adaptive and barrier loci through reduced recombination, promote or prevent introgression.
• We conducted a hybridize, evolve, and re-sequence experiment by crossing the heat-sensitive D.
• montana, exposing heat-selection lines to transient heat for three generations while maintaining control lines.
• We also mapped long-term barriers to gene flow between natural populations using a demographically explicit genome scan.
• The heat-selection lines exhibited approximately twice the introgression and higher male fertility under heat stress compared to control lines and the heat-sensitive parental D.

What to take from it

This introgression was primarily located in colinear autosomal regions and correlated with improved heat tolerance. Some introgression occurred also in inverted autosomal regions in the heat-selection lines but not in the control lines. The X chromosome, with three overlapping inversions, resisted introgression in both heat-selection and control lines, thereby maintaining a strong species barrier.

Example or evidence

• Our study demonstrates that strong selection can lead to adaptive introgression despite long-standing genetic barriers.