Evidence of multiple vicariance in a marine suture-zone in the Gulf of Mexico

Aim Our aim was to assess whether single or multiple vicariance event(s) have occurred in a marine suture-zone in the northern Gulf of Mexico. We estimated the divergence time of two genetically distinct groups of lane snapper (Lutjanus synagris), distributed on either side of this zone, and compared it to the timing of other vicariance events described previously in the area. Location The northern Gulf of Mexico from the Texas coastline to the Atlantic coast of South Florida, USA. The marine suture-zone is proximal to Mobile Bay in Alabama. Methods A Bayesian Markov chain Monte Carlo (MCMC) approach was used to estimate mutation-corrected divergence and genetic migration between eastern and western groups of lane snapper, based on genotypic differences at 13 nuclear-encoded microsatellites obtained previously from 77 and 171 individual samples, respectively. A second estimate of divergence time for eastern and western groups of lane snapper was generated, based on 590 base pairs of DNA sequence from the mitochondrially encoded NADH dehydrogenase subunit 4 (ND4) obtained previously from 45 and 93 individual samples, respectively. Results Both classes of genetic markers (microsatellites and mtDNA) indicated a fairly recent divergence. Confidence intervals for microsatellite-based estimates suggested that divergence began less than 21 thousand years ago (ka), while confidence intervals for mitochondrial DNA-based estimates suggested divergence began less than 130 ka. These estimates were not consistent with vicariance events in the literature, which are hypothesized to have occurred well before 135 ka. Main conclusions These results indicate that the marine suture-zone in the northern Gulf of Mexico features multiple vicariance events and may be characterized by a complex geological/environmental history. We suggest that processes during or after the Wisconsin glaciation (c. 11018 ka) may have created a previously unrecognized barrier for lane snapper and possibly other species as well.