Parallel speciation or long-distance dispersal? Lessons from seaweeds (Fucus) in the Baltic Sea

Area of Science:

• Marine biology
• Evolutionary genetics
• Speciation research

Background:

• Parallel evolution is a key mechanism in species formation, but distinguishing it from recent divergence with hybridization can be challenging.
• Reproductive isolation, dispersal barriers, and long-distance dispersal capacity influence demographic structures critical for divergent evolution.

Purpose of the Study:

• To investigate intra- and interspecific genetic diversity of two closely related brown algae species, Fucus radicans and Fucus vesiculosus, in the Baltic Sea.
• To explore the role of connectivity patterns in shaping genetic structures using biophysical modeling.

Main Methods:

• Utilized nine microsatellite DNA markers to analyze genetic diversity within and between F. radicans and F. vesiculosus populations.
• Employed biophysical modeling to assess potential marine connectivity influencing genetic patterns.

Main Results:

• Observed contrasting intraspecific patterns of clonality and population structure for each species.
• Detected strong genetic differentiation between F. radicans and F. vesiculosus, supporting distinct evolutionary lineages (FST = 0.15-0.41).
• Genetic clustering revealed populations from Estonia were more similar to each other than to conspecific populations from Sweden and Finland.

Conclusions:

• Data supports a hypothesis of parallel speciation between F. radicans and F. vesiculosus.
• An alternative hypothesis suggests Estonia as an ancestral source, with oceanographic barriers limiting gene flow and genetic drift driving observed genetic structures.