Niche divergence contributes to geographical parthenogenesis in two dandelion taxa

Distinct geographic parthenogenesis in spite of niche conservatism and a single ploidy level: A case of Rubus ser. Glandulosi (Rosaceae)

Asexual organisms often differ in their geographic distributions from their sexual relatives. This phenomenon, termed geographic parthenogenesis, has long been known, but the underlying factors behind its diverse patterns have been under dispute. Particularly problematic is an association between asexuality and polyploidy in most taxa. Here, we present a new system of geographic parthenogenesis on the tetraploid level, promising new insights into this complex topic. We used flow cytometric seed screen and microsatellite genotyping to characterise the patterns of distribution of sexuals and apomicts and genotypic distributions in Rubus ser. Glandulosi across its range. Ecological modelling and local-scale vegetation and soil analyses were used to test for niche differentiation between the reproductive groups. Apomicts were detected only in North-western Europe, sexuals in the rest of the range in Europe and West Asia, with a sharp borderline stretched across Central Europe. Despite that, we found no significant differences in ecological niches. Genotypic richness distributions suggested independence of the reproductive groups and a secondary contact. We argue that unless a niche differentiation (resulting from polyploidy and/or hybridity) evolves, the main factors behind the patterns of geographic parthenogenesis in plants are phylogeographic history and neutral microevolutionary processes, such as clonal turnover.

Taxonomy and distribution of Taraxacum sect. Erythrosperma (Asteraceae) in Poland

The dandelions from Taraxacumsect.Erythrosperma are taxonomically well distinguished and ecologically restricted to warm and sunlit habitats of steppes, dry and sandy grasslands, and distributed in temperate regions of Europe and Central Asia, with some being introduced to North America. Despite the long tradition of botanical research, the taxonomy and distribution of dandelions of T.sect.Erythrosperma is still underexplored in central Europe. In this paper, by combining traditional taxonomic studies supported by micromorphological, molecular and flow cytometry analyses as well as potential distribution modelling we shed light on taxonomical and phylogenetical relationships between members of T.sect.Erythrosperma in Poland. We also provide an identification key, species-checklist, detailed descriptions of morphology and occupated habitats as well as distribution maps for 14 Polish erythrosperms (T.bellicum, T.brachyglossum, T.cristatum, T.danubium, T.disseminatum, T.dissimile, T.lacistophyllum, T.parnassicum, T.plumbeum, T.proximum, T.sandomiriense, T.scanicum, T.tenuilobum, T.tortilobum). Finally, conservation assessments performed using the IUCN method and threat categories for all the examined species are proposed.

Geographical Parthenogenesis in Alpine and Arctic Plants

The term "Geographical parthenogenesis" describes the phenomenon that asexual organisms usually occupy larger and more northern distribution areas than their sexual relatives, and tend to colonize previously glaciated areas. Several case studies on alpine and arctic plants confirm the geographical pattern, but the causal factors behind the phenomenon are still unclear. Research of the last decade in several plant families has shed light on the question and evaluated some of the classical evolutionary theories. Results confirmed, in general, that the advantages of uniparental reproduction enable apomictic plants to re-colonize faster in larger and more northern distribution areas. Associated factors like polyploidy seem to contribute mainly to the spatial separation of sexual and asexual cytotypes. Ecological studies suggest a better tolerance of apomicts to colder climates and temperate extremes, whereby epigenetic flexibility and phenotypic plasticity play an important role in occupying ecological niches under harsh conditions. Genotypic diversity appears to be of lesser importance for the distributional success of asexual plants. Classical evolutionary theories like a reduced pressure of biotic interactions in colder climates and hence an advantage to asexuals (Red Queen hypothesis) did not gain support from studies on plants. However, it is also still enigmatic why sexual outcrossing remains the predominant mode of reproduction also in alpine floras. Constraints for the origin of apomixis might play a role. Interestingly, some studies suggest an association of sexuality with abiotic stresses. Light stress in high elevations might explain why most alpine plants retain sexual reproduction despite other environmental factors that would favor apomixis. Directions for future research will be given.

Niche Divergence at Intraspecific Level in the Hyrcanian Wood Frog, Rana pseudodalmatina: A Phylogenetic, Climatic, and Environmental Survey

The role of ecological niche divergence in lineage speciation has recently stimulated the interest of evolutionary biologists and ecologists. Phylogenetic analysis has revealed that the Hyrcanian wood frog, Rana pseudodalmatina, has diverged into two western and eastern regional clades (WRC and ERC) within the Hyrcanian forest. The goal of this study was to investigate whether the ecological niches of WRC and ERC are conserved or diverged, as well as to figure out what variables promote niche conservatism or divergence. For this purpose, the maximum entropy model was employed to assess environmental niche modeling in geographical (G) space utilizing climatic and macro-environmental data. The niche overlap, equivalency, and similarity tests based on PCAenv analyses were used to assess niche divergence or conservatism in environmental (E) space. The findings strongly support the hypothesis that WRC and ERC have undergone substantial niche divergence and are constrained by a unique set of climatic and macro-environmental conditions. This study by ecological niche comparisons based on phylogenetic data provides new insights into the exploration of species diversification processes in the Hyrcanian forests.

Niche divergence contributes to geographical parthenogenesis in two dandelion taxa

Many sexual-asexual complexes show a distinct pattern where the asexuals have larger and more northerly ranges than closely related sexuals. A prime candidate to explain this so-called "geographical parthenogenesis" is ecological niche divergence between the sexuals and asexuals. Modern niche modelling techniques allow testing niche divergence by directly comparing the niches of sexuals and asexuals. In this study, I use such techniques to perform range-wide tests of whether nine bioclimatic variables, including annual mean temperature and annual precipitation, contribute to geographical parthenogenesis in two dandelion taxa: Taraxacum section Ruderalia and Taraxacum section Erythrosperma, which are both comprised of sexual diploids and asexual triploids. For both sections, I found evidence of niche divergence, though the exact nature of this divergence was different for the two sections. In section Ruderalia, the sexuals preferred warmer and wetter conditions, whereas in section Erythrosperma, the sexuals preferred dryer conditions. Using Species Distribution Modelling, consistent differences between the sexuals and asexuals were found when looking at the niche determinants: the variables that are most important for modelling the distribution. Furthermore, and in contrast with theoretical expectations that predict that the sexuals should have a wider niche, in section Erythrosperma the asexuals were found to have a wider niche than the sexuals. In conclusion, differences in niche optima, niche determinants, and niche width all contribute to the pattern of geographical parthenogenesis of these two dandelion taxa. However, the results also indicate that the exact causation of geographical parthenogenesis is not uniform across taxa.