Application of non-coding DNA regions in intraspecific analyses

In this review we discuss the use of non-coding DNA at the intraspecific level in plants. Both nuclear and organelle non-coding regions are widely used in interspecific phylogenetic approaches. However, they are also valuable in analyses on the intraspecific level. Besides taxonomy, that is, defining subspecies or varieties, large fields for the application of non-coding DNA are population genetic and phylogeographic studies. Population genetics tries to explain the genetic patterns within species mostly by the amount of extant gene flow among populations, while phylogeography explicitly tries to reconstruct historic events. Depending on the study different molecular markers can be used, varying between very fast evolving microsatellites or some more slowly changing regions like intergenic spacers and introns. Here, we focus mainly on the use of non-coding regions in phylogeographic analyses. Mostly used in this context are regions of the genomes of the chloroplasts and mitochondria. In phylogeography, the correct estimation of allele or haplotype relationships is particularly important. As tree-based methods are mostly insufficient to depict relationships within species, network approaches are better suitable to infer gene or locus genealogies. Problematic for phylogeographic studies are alleles shared among multiple species, which could result from either hybridization or incomplete lineage sorting. Especially the latter can severely influence the interpretation of the phylogeographic patterns. Therefore, it seems necessary for us to also include close relatives of the species under study in phylogeographic analyses. Not only the sample design but also the analysis methods are currently changing, as some new methods such as statistical phylogeography were emerging recently and widely used methods like nested clade analysis might not be reliable in every case. During the last few years, a multitude of studies were published, which mainly analyzed phylogeographic patterns in European and North American plants. Phylogeographic studies in other regions of the earth are still comparably rare, although questions like the influence of the ice age on the vegetation in the tropics or southern hemisphere are still open and phylogeography provides an excellent remedy to answer them.