Reevaluating claims of ecological speciation in Halichoeres bivittatus

Allopatry has traditionally been viewed as the primary driver of
speciation in marine taxa, but the geography of the marine environment and
the larval dispersal capabilities of many marine organisms render this
view somewhat questionable. In marine fishes, one of the earliest and most
highly cited empirical examples of ecological speciation with gene flow is
the slippery dick wrasse, Halichoeres bivittatus. Evidence for this
cryptic or incipient speciation event was primarily in the form of a deep
divergence in a single mitochondrial locus between the northern and
southern Gulf of Mexico, combined with a finding that these two haplotypes
were associated with different habitat types (“tropical” vs.
“subtropical”) 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. We find no evidence to support the claim that haplotype frequencies
differ between habitat types, and little evidence to support any
differences between populations in the Keys. These results undermine
claims of ecological speciation with gene flow in Halichoeres bivittatus.
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.