Reevaluating claims of ecological speciation in Halichoeres bivittatus

Abstract

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.

Assessing temporal biases across aggregated historical spatial data: a case study of North Carolina’s freshwater fishes

“…Over the past century, numerous logistical problems associated with sampling, including accessibility (Willis andBabcock 2000, Koenig andStallings 2015), as well as biases in the efficiency and detection rates of different monitoring equipment (Kjelson and Colby 1977, Beamesderfer and Rieman 1988, Dornburg et al 2017b, have had to be overcome. These efforts have resulted in an unprecedented picture of the spatial distribution of fishes that has been fundamental for studies of niche modeling (Bond et al 2011, Ruaro et al 2019, McMahan et al 2020, biogeography (Dornburg et al 2015, 2017a, Cowman et al 2017, Siqueira et al 2019, and population genetics (Rocha 2003, Echelle et al 2015, Healey et al 2018, Warren et al 2021 to name but a few. However, the potential that underlying biases persist in this aggregated data remains.…”