Separating population structure from population history: a cladistic analysis of the geographical distribution of mitochondrial DNA haplotypes in the tiger salamander, Ambystoma tigrinum.

TLDR

Nonrandom associations of alleles or haplotypes with geographic location can arise from restricted gene flow, historical events such as fragmentation, range expansion, or colonization, or a mixture of these factors. The study demonstrates how nested cladistic analysis of geographic distances can test for no association, attribute significant associations to restricted gene flow, and identify patterns due to historical events. The method employs nested cladistic analysis with criteria to distinguish contiguous range expansion, long‑distance colonization, and fragmentation, depends on adequate geographic sampling, and is illustrated using mitochondrial DNA haplotypes from Ambystoma tigrinum. Analyses of Ambystoma tigrinum haplotypes matched prior expectations of restricted gene flow and historical events, supporting the method’s plausibility while indicating further work is needed to assess robustness and accuracy.

Abstract

Abstract Nonrandom associations of alleles or haplotypes with geographical location can arise from restricted gene flow, historical events (fragmentation, range expansion, colonization), or any mixture of these factors. In this paper, we show how a nested cladistic analysis of geographical distances can be used to test the null hypothesis of no geographical association of haplotypes, test the hypothesis that significant associations are due to restricted gene flow, and identify patterns of significant association that are due to historical events. In this last case, criteria are given to discriminate among contiguous range expansion, long-distance colonization, and population fragmentation. The ability to make these discriminations depends critically upon an adequate geographical sampling design. These points are illustrated with a worked example: mitochondrial DNA haplotypes in the salamander Ambystoma tigrinum. For this example, prior information exists about restricted gene flow and likely historical events, and the nested cladistic analyses were completely concordant with this prior information. This concordance establishes the plausibility of this nested cladistic approach, but much future work will be necessary to demonstrate robustness and to explore the power and accuracy of this procedure.