A 'Bermuda Triangle' Effect Shaping Reef Fish Connectivity Across the Western Atlantic

Area of Science:

• Marine Biology
• Population Genetics
• Oceanography

Background:

• Marine connectivity is crucial for understanding gene flow and population structure in reef organisms.
• Ocean currents significantly influence larval transport and genetic exchange.

Purpose of the Study:

• To examine range-wide patterns of gene flow and population structure in the tomtate (Haemulon aurolineatum).
• To assess connectivity, demographic history, and lineage boundaries across the species' distribution in the western Atlantic.

Main Methods:

• Utilized genome-wide single nucleotide polymorphisms (SNPs) and mitochondrial DNA sequences.
• Incorporated a re-evaluation of morphological variation across 22 locations.
• Employed population structure, phylogenetic analyses, demographic modeling, and coalescent-based species delimitation.

Main Results:

• Identified three main genetic groups: Caribbean/Southwestern Atlantic (CSA), Gulf of Mexico (GOM), and Bermuda (BDA).
• Revealed early divergence with sustained, asymmetric gene flow, particularly into Bermuda, acting as a demographic sink.
• Marine barriers (e.g., Caribbean breaks) contributed to differentiation, while coastal corridors facilitated gene flow.

Conclusions:

• Asymmetric dispersal and oceanographic isolation structure genetic diversity in marine organisms.
• Peripheral demographic sinks, like Bermuda, promote long-term genetic differentiation (the 'Bermuda Triangle effect').
• Identified three distinct lineages, interpreted as subspecies, not fully reproductively isolated.