Understanding the role of ecological processes in speciation has become
one of the most active areas of research in marine population biology in
recent decades. The traditional view was that allopatry was the primary
driver of speciation in marine taxa, but the geography of the marine
environment and the dispersal capabilities of many marine organisms
render this view somewhat questionable. One of the earliest and most
highly cited empirical examples of ecological speciation with gene flow
in marine fishes is that of the slippery dick wrasse, Halichoeres
bivittatus. Evidence for this cryptic or incipient speciation event was
primarily in the form of a deep north-south divergence in a single
mitochondrial locus, combined with a finding that these two haplotypes
were associated with different habitat types in the Florida Keys and
Bermuda, where they overlap. Here we examine habitat assortment in the
Florida Keys using a broader sampling of populations and habitat types
than were available for the original study, and find no evidence to
support the claim that haplotype frequencies differ between habitat
types, and little evidence to support any differences between
populations. These results severely undermine claims of ecological
speciation with gene flow in Halichoeres bivittatus. We argue that
future claims of this type should be supported by multiple lines of
evidence that illuminate potential mechanisms and allow researchers to
rule out alternative explanations for spatial patterns of genetic
differences.