Two new hybrid populations expand the swordtail hybridization model system

Area of Science:

• Evolutionary Biology
• Genetics
• Ichthyology

Background:

• Natural hybridization offers insights into species divergence and reproductive isolation.
• Swordtail fish (Xiphophorus) provide a model system for studying hybridization dynamics.

Purpose of the Study:

• To characterize the genetic structure of hybrid populations between Xiphophorus cortezi and Xiphophorus birchmanni.
• To investigate the role of assortative mating in maintaining distinct hybrid subpopulations.

Main Methods:

• Utilized simulations and genetic reference panels for local ancestry calling.
• Analyzed hybrid populations from two river systems.

Main Results:

• Identified two distinct subpopulations: pure X. birchmanni and intermediate hybrids with ~85-90% X. cortezi ancestry.
• Estimated initial hybridization ~150 generations ago with limited contemporary gene flow.
• Observed population structure consistent with strong assortative mating.

Conclusions:

• Assortative mating plays a significant role in shaping hybrid population structure in Xiphophorus.
• Hybridization patterns between X. birchmanni and X. cortezi mirror those with X. malinche, suggesting conserved evolutionary mechanisms.
• Further research can elucidate shared drivers of hybridization outcomes across species.