Introgressive hybridization and latitudinal admixture clines in North Atlantic eels

Area of Science:

• Evolutionary Biology
• Genetics
• Marine Biology

Background:

• Hybridization between divergent species is crucial for evolutionary studies.
• North American and European eels migrate to the Sargasso Sea to mate, but reproductive isolation mechanisms are unclear.
• Evidence of inter-species hybrids suggests ongoing gene flow, yet the impact of introgression on North Atlantic eel genetic differentiation remains understudied.

Purpose of the Study:

• To investigate the extent of hybridization and introgression between North Atlantic eel species.
• To understand how gene flow influences genetic differentiation in these eel populations.
• To test hypotheses regarding recent introgression versus ancient polymorphism.

Main Methods:

• Analysis of mitochondrial and nuclear DNA markers to detect hybridization.
• Bayesian assignment analyses to map hybridization patterns across geographic ranges.
• Simulation of F1 hybrids and admixed individuals to model isolation-by-distance patterns.
• Fitting an isolation-with-migration model to assess introgression dynamics.

Main Results:

• Mitochondrial lineages of North American and European eels are distinct.
• Nuclear DNA markers reveal limited hybridization, with the signal strongest in northern regions and decreasing southward.
• Simulations successfully replicated observed isolation-by-distance patterns, supporting introgression.
• The isolation-with-migration model favored recent asymmetric introgression over ancient polymorphism.

Conclusions:

• Fluctuating levels of introgressive hybridization between Atlantic eel species adequately explain observed genetic and geographic distance correlations in European eel populations.
• Recent introgression, rather than ancient polymorphisms, is the primary driver of current genetic patterns.
• Understanding introgression is key to comprehending the evolutionary dynamics of North Atlantic eels.