Data from: The K=2 conundrum

Assessments of population genetic structure have become an increasing
focus as they can provide valuable insight into patterns of migration and
gene flow. STRUCTURE, the most highly cited of several clustering-based
methods, was developed to provide robust estimates without the need for
populations to be determined a priori. STRUCTURE introduces the problem of
selecting the optimal number of clusters and as a result the ΔK method was
proposed to assist in the identification of the ‘true’ number of clusters.
In our review of 1,264 studies using STRUCTURE to explore population
subdivision, studies that used ΔK were more likely to identify K=2 (54%,
443/822) than studies that did not use ΔK (21%, 82/386). A troubling
finding was that very few studies performed the hierarchical analysis
recommended by the authors of both ΔK and STRUCTURE to fully explore
population subdivision. Furthermore, extensions of earlier simulations
indicate that, with a representative number of markers, ΔK frequently
identifies K=2 as the top level of hierarchical structure, even when more
subpopulations are present. This review suggests that many studies may
have been over- or underestimating population genetic structure; both
scenarios have serious consequences, particularly with respect to
conservation and management. We recommend publication standards for
population structure results so that readers can assess the implications
of the results given their own understanding of the species biology.