Phylogeny & Phylogeography of Androsace sect. Aretia

Disjunction, the occurrence of fragmented distributions within a taxon, is one of the most fascinating phenomena in biogeography. The investigation of disjunctions can provide insights into processes such as speciation, extinction, changes of distributional areas (expansion, restriction), or colonization. Depending on the rank of the investigated taxon, two avenues of research can be taken: (1) the phylogenetic approach from the specific rank upwards, or (2) the phylogeographic approach from the specific rank downwards. Androsace sect. Aretia (Primulaceae) provides an excellent model system for research at the interface of phylogeny and phylogeography. This group comprises ca. 20 closely related, morphologically well-defined species with similar dispersal abilities and floral syndromes. It is distributed in the southern and central European mountain ranges with centres of species-richness in the Alps and the Pyrenees. Both vicariance of sister taxa and intraspecific disjunctions are present. The following questions can be addressed with this model system: (1) Is the species-richness in the Alps and Pyrenees due to in situ-radiation (cladogenesis) or multiple colonization events with subsequent anagenetic speciation? (2) What are the phylogeographical patterns of widely distributed but disjunct species? Are these disjunctions due to (ancient) range fragmentation or due to rather recent long-distance dispersal events? (3) How deep are the major splits within widely but disjunctly distributed species compared to those between sister-taxa? Are there cryptic taxa to be discovered? We apply a set of complementary molecular and cytogenetic techniques to address these questions: DNA- sequencing, AFLP (Amplified Fragment Length Polymorphism), PCR-RFLP (restriction fragment length polymorphism) of chloroplast DNA, FISH (Fluorescence in situ-hybridization). The power of this study lies in two points: 1) Comparative phylogeography of closely related biologically very similar species. Comparative phylogeography in general allows investigating processes such as dispersal of taxa through a region, speciation, adaptive radiation, and extinction. 2) Synthesis of phylogeny and comparative phylogeography will yield a much broader basis to address two questions of interest going far beyond the group investigated: biogeography of the alpidic European mountain system; and the delimitation of species by comparison of the genetic divergence of sister-species and intraspecific isolated entities.

Phylogeography deals with the geographic distribution of genealogical lineages, usually within species, in order to reconstruct the origins and diffusion of lineages. While phylogeographic studies of single species are interesting in themselves, they are not sufficient to investigate general processes at work in shaping organisms` distribution. Therefore, combining results from several species is required, a field known as comparative phylogeography. While the majority of comparative phylogeographic studies use a group of species with similar distributions, we instead investigated a group of closely related species with essentially identical biological characteristics - in particular concerning pollination and dispersal ecology - but dissimilar distribution areas. An excellent model system for this approach is the European endemic high mountain group Androsace sect. Aretia (Primulaceae), whose c. 20 species show different distribution patterns ranging from widespread to local distributions with both contiguous or more or less highly fragmented distribution areas. Four broad conclusions can be drawn from our investigations: (i) The widespread inference that geographically wide, but fragmented distribution, especially if more or less confined to putative (Pleistocene) refugial areas, are remnants of a wide ancient distribution, is often false (e.g., Androsace lactea, A. vitaliana). (ii) Long distance dispersals play a significant role in shaping current distributions and may involve counter- intuitive combinations of mountain ranges, e.g., between the Alps and the NW Iberian Cordillera Cantbrica sparing the geographically intermediate Pyrenees (e.g., Androsace cantabrica, A. vitaliana). (iii) Gene flow, both ancient and current, due to hybridisation and introgression is prominent, resulting in reticulate relationships (e.g., A. adfinis group, A. halleri group). This also emphasizes the need to investigate data from different genomes, as different contradicting data sets allow elucidating different aspects of a species` history. (iv) Despite the high degree of similarity concerning pollination and dispersal biology, each species or species- group has a highly idiosyncratic history, indicating that common processes shaping species` distributions, if present at all, are much more subtle than suggested by established phylogeographic paradigms. As a by-product of the in depth phylogeographic investigations, populations from the eastern Pyrenees so far treated as A. halleri and from Crna Gora (Montenegro) so far treated as A. mathildae are recognised as new species.