Detecting migration routes and barriers by examining the distribution of species in an apomictic species complex
The distribution of taxa (‘microspecies’) in the apomictic species complexes Hieracium L. sect. Hieracium and H. sect. Vulgata (Griseb.) Willk. and Lange have been analysed to test whether the geographical distribution of species within each complex will reflect historical processes and phenomena, e.g. historical barriers to migration and range expansion. It is argued that apomictic species can be used for phylogeographic analysis in the same way as organelle haplotypes or multilocus genotypes.Location
The investigated area is the Nordic countries excluding Iceland, together with the Baltic islands of Saarema (Estonia) and Rügen (Germany).Methods
The presence or absence of 160 species of H. sect. Hieracium and 165 species of H. sect. Vulgata was recorded in 39 geographical areas. Based on this dataset, Jaccard similarity indices were calculated and subjected to upgma cluster analysis and non-metric multidimensional scaling (MDS).Results
For both species complexes, the larger water surfaces were found to represent discontinuities in species composition, interpreted as migration barriers. Some inland migration barriers were also indicated, e.g. in northern-central Sweden. The Scandes seems to have constituted a migration barrier for H. sect. Vulgata. Some areas in south-western Sweden represent discontinuities in the distribution of species within H. sect. Hieracium.Main conclusions
The revealed geographical patterns in species composition, as well as the differences in the patterns for the two species complexes, are readily explainable as reflecting historical migration routes and barriers. Further analysis using apomictic taxa as ‘markers’ may give important phylogeographic insights. The pros and cons of using microspecies, as opposed to molecular markers, in historical biogeography is discussed.