| dc.description.abstracteng | Accurate species identification and assessment of species diversity are essential for studies on phylogeny and phylogeography, adaptation and ecological function. The development of molecular methods triggered the discovery of cryptic species, i.e., genetically distinct lineages in morphologically undifferentiated species. Collembola (Arthropoda, Hexapoda) are one of the most numerous soil-living animals occurring in virtually all terrestrial ecosystems and habitats. Species delimitation is particularly difficult in Collembola due to considerable morphological conservatism, and many Collembola species comprise high genetic divergence and high cryptic species diversity. DNA-based methods provide useful tools for species delimitation, phylogenetic reconstruction, and lineage divergence time estimation. By analyzing two mitochondrial and two nuclear genes from three morphospecies of the European Lepidocyrtus lanuginosus species group (Collembola: Entomobryidae) from different geographic regions of Europe, this thesis focuses on exploring cryptic species / lineages diversity, their phylogeny, and the effects of historical geographic and climatic changes on the divergence and distribution of this species group in Europe.
In chapter II, I investigated phylogenetic relationships and genetic distances between populations of the morphospecies L. lanuginosus (Gmelin, 1788) from three different habitats in Central Europe, i.e. arable fields, grasslands, and forests replicated at six locations. Geographic distances between sampling locations were considerably larger than between habitat types. All four genes clearly separated the morphospecies L. lanuginosus into three major genetic lineages, with one of these lineages being close to Lepidocyrtus cyaneus Tullberg, 1871. The three lineages were genetically as distant to each other as well separated species. Selective colonization of the three habitats by these lineages indicate that they are sorted by habitats: one lineage was common and occurred in each of the three habitat types but preferentially in arable land; the second was restricted to forest; the third, although rare, preferentially occurred in grassland. The results indicate that genetic markers are a reliable and fast method to detect cryptic species, which may facilitate taxonomic research on Collembola species and the identification of possible species-specific morphological characters.
In Chapter III, I delimited species boundaries of the L. lanuginosus species group sampled across Central and Southern Europe (north and south of the Alps) by utilizing three DNA-based methods, ABGD, PTP, and BPP. Species diversity delimited by morphology was compared with that delimited by genes. Three methods based on mitochondrial COI and COII congruently identified ten and nine distinct genetic lineages in the morphospecies L. cyaneus and L. lanuginosus, respectively. ABGD delimitated species barcoding gaps with K2P distances of 0.055–0.095 and 0.06–0.115 for COI and COII, respectively, within the species group. EF1-α separated 89% of these lineages, showing a higher resolution than 28S rDNA D1–2 in distinguishing closely related genetic lineages of the species group. The phylogenetic analysis based on the four genes showed that both morphospecies L. cyaneus and L. lanuginosus are polyphyletic, suggesting that body color is insufficient for delimiting morphospecies and lineages in this Collembola species group. This study challenges the current morphology-based species delimitation in the L. lanuginosus species group and suggests that molecular approaches are needed for accurate determination of Collembola species in both taxonomic and ecological studies. Overall, the results suggest that wide geographic sampling combined with molecular phylogenetic approaches is necessary to delimit species, understand the full range of cryptic diversity, and analyze phylogenetic relationships in Collembola.
In Chapter IV, I studied the phylogeography of 18 lineages of the L. lanuginosus species group using a multi-locus molecular approach. The genetic diversity and population structure of all lineages were analyzed using COII, while all four above-mentioned genes were concatenated to infer the phylogeographic origin of these lineages. Results showed that the 18 lineages did not overlap in their distribution ranges in Central, Southern, and Southeastern Europe, suggesting high genetic structure and limited gene flow between these three regions. The major lineages diverged in the Late Miocene and Pliocene (17–2.59 million years ago, Mya), i.e. before Quaternary ice ages, indicating that distinct lineages survived in multiple refugia in each sampling region during Quaternary glacial periods. The genetic structure of the 18 lineages of the group supported a model of sequential allopatric diversification within each sampling region. Further, three distinct lineages which diverged during the Pleistocene and Holocene were widely distributed across Central Europe, suggesting that glacial cycles in the Quaternary affected the spread of these lineages. Identical haplotypes of both of these lineages, occurring in localities hundreds of kilometers apart, suggest recent human-mediated dispersal across Central Europe. These results indicate that distribution patterns of Collembola in Europe are more complex than previously assumed.
By utilizing DNA-based analyses, my thesis highlights a novel view of the diversity, ecology, phylogeny, and phylogeography of the three morphospecies of the European L. lanuginosus species group. DNA-based analyses rejected the three-species hypothesis based on the morphological species concept and the monophyly of each species based on the phylogenetic species concept. This suggests that historical geographic and climatic changes dating to the late Miocene as well as recent human-mediated dispersal caused the lineage divergence and shaped the present-day distribution of this species group. Environmental factors other than geographic distances likely impede gene flow among lineages. Overall, the results of this thesis suggest that soil animals likely experienced different and more complex evolutionary forces than aboveground animals and plants in shaping their genetic diversification and biogeographic distribution. Future studies need to explore the physiological characters responsible for habitat sorting of cryptic species / lineages of the L. lanuginosus species group, and global scale phylogeographic studies on a number of Collembola species are needed for a deeper understanding of the dispersal, speciation, and evolution of Collembola and of soil animals in general. | de |