Many mountain ranges have been strongly glaciated during the Quaternary ice ages, and the locations of glacial refugia of mountain plants have been debated for a long time. A series of detailed molecular studies, investigating intraspecific genetic variation of mountain plants in the European Alps, now allows for a first synopsis. A comparison of the phylogeographic patterns with geological and palaeoenvironmental data demonstrates that glacial refugia were located along the southwestern, southern, eastern and northern border of the Alps. Additional glacial refugia were present in central Alpine areas, where high-elevation plants survived the last glaciation on ice-free mountain tops. The observed intraspecific phylogeographies suggest general patterns of glacial survival, which conform to well-known centres of Alpine species diversity and endemism. This implies that evolutionary or biogeographic processes induced by climatic fluctuations act on gene and species diversity in a similar way.

Two main possibilities regarding glacial survival of the mountain flora of the Alps during the Quaternary have been discussed: the tabula rasa and the nunatak hypotheses. Eritrichium nanum (L.) Gaudin (Boraginaceae) is a perennial cushion plant, occurring at high elevations of the Central Alps and having a preference for extreme habitats. It belongs to a group of high-alpine plants, for which in situ glacial survival on nunataks is ecologically possible. By investigating 20 populations of E. nanum of potential nunatak and peripheral refugial regions using amplified fragment length polymorphism, considerable genetic differences between populations from the Central Alps and populations from peripheral refugia were detected; hence, the latter probably did not serve as potential sources for the re-colonization of the Central Alps after glaciation. Genetic variation was hierarchically structured (AMOVA), and three genetically distinct regions could be identified in the Central Alps. Two of these, the Penninic and Rhaetic Alps, correspond to nunatak regions proposed in the biogeographic literature. Populations from the Lepontic Alps formed a third genetic group. Genetic correlation (Mantel statistics) was highest within populations, with a modest decline among populations within specific nunatak regions and a negative correlation outside the genetic influence of specific nunatak regions. In situ glacial survival in E. nanum could be a model for the Quaternary history of other alpine plants, especially those that also occur at high elevations and in similar habitats.

Polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLPs) and sequence analysis of noncoding regions of chloroplast DNA were used to investigate 37 populations of Eritrichium nanum covering its total distribution area, the European Alps. There was no haplotypic variation within the populations, and most haplotypes were restricted to single sites or to neighbouring populations, suggesting low levels of long distance gene flow via seeds. The present geographical distribution of haplotypes probably reflects an ancient geographical pattern within two regions in the intensely glaciated western and eastern central Alps identified as genetic hotspot areas. These two regions contained seven of the total of 11 haplotypes, including many of the most derived ones. The divergent haplotypes formed closely related groups, which supported a separate evolution of these haplotypes in these two regions and, more importantly, gave strong evidence for the in situ survival of these populations on nunataks within the western and eastern central Alps during Pleistocene glaciation. This result is in concordance with a previous study on E. nanum using nuclear markers. Only one haplotype was common and widespread throughout the distributional range of E. nanum. At the same time, it was the evolutionarily basal-most and all other haplotypes were best described as its descendants. This haplotype is hypothesized to be genetically identical to a Tertiary Alpine colonizing ancestor, whose distribution was secondarily fragmented and infiltrated by derived haplotypes originating through local mutations.

There is considerable controversy concerning the fate of Alpine plants during Pleistocene glaciations. While some studies have found evidence for nunatak survival, others have explained the present genetic patterns by survival only in peripheral refugia. We investigated 75 populations of high alpine Ranunculus glacialis from its entire Alpine distribution. Phylogeographical analyses of AFLP data revealed four groups of populations. Two of them, located in the western Alps, were genetically isolated from each other and from the eastern groups, whereas the two eastern Alpine groups were genetically more similar to each other. This suggests longer isolation and/or lower levels of gene flow in the two western groups. As all groups are close to, or overlap with, presumed glacial refugia, invoking glacial survival on nunataks is unnecessary to explain the present genetic pattern. Similar to the phylogeographical patterns of R. glacialis , the previously investigated alpine Phyteuma globulariifolium and Androsace alpina , which are also confined to siliceous bedrock, showed strong geographical affinities to peripheral refugial areas and there were large-scale congruencies in the location of these refugia for all three species.

Sex ratios of flowering individuals in dioecious plant populations are often close to unity, or are male biased owing to gender-specific differences in flowering or mortality. Female-biased sex ratios, although infrequent, are often reported in species with heteromorphic sex chromosomes. Two main hypotheses have been proposed to account for female bias: (1) selective fertilization resulting from differential pollen-tube growth of female- versus male-determining microgametophytes (certation); (2) differences in the performance and viability of the sexes after parental investment. Here we investigate these hypotheses in Rumex nivalis (Polygonaceae), a European alpine herb with female-biased sex ratios in which females possess XX, and males XY1Y2, sex chromosomes. Using field surveys and a glasshouse experiment we investigated the relation between sex ratios and life-history stage in 18 populations from contrasting elevations and snowbed microsites and used a male-specific SCAR-marker to determine the sex of nonflowering individuals. Female bias among flowering individuals was one of the highest reported for populations of a dioecious species (mean female frequency = 0.87), but males increased in frequency at higher elevations and in the center of snowbeds. Female bias was also evident in nonflowering individuals (mean 0.78) and in seeds from open-pollinated flowers (mean 0.59). The female bias in seeds was weakly associated with the frequency of male flowering individuals in populations in the direction predicted when certation occurs. Under glasshouse conditions, females outperformed males at several life-history stages, although male seeds were heavier than female seeds. Poor performance of Y1Y2 gametophytes and male sporophytes in R. nivalis may be a consequence of the accumulation of deleterious mutations on Y-sex chromosomes.

There is a long‐standing debate about the fate of the mountain flora of the European Alps during the Pleistocene ice ages. Two main scenarios of glacial survival of alpine plant taxa have been discussed, namely (1) total extinction within glaciated areas, survival in peripheral refugia, and postglacial re‐immigration into vacant areas (tabula rasa hypothesis), and (2) long‐term in situ survival within glaciated regions in isolated ice‐free areas above the ice‐shield (nunatak hypothesis). Four alpine species with differing distributions and ecological demands were investigated to elucidate their glacial history using molecular methods (AFLPs, RFLPs of cpDNA, RAPDs). Their glacial histories are very diverse. Whereas in situ survival in the most intensely glaciated Central Alps played an important role in Eritrichium nanum, the low alpine Erinus alpinus survived in situ on some mountains of the northern Swiss Prealps, and Rumex nivalis grows at intermediate alpine elevations in snow‐beds in both the northern and the Central Swiss Alps. In the common arctic‐alpine Saxifraga oppositifolia, the species with the widest distribution and ecological amplitude as compared to the other three species, it is not possible to reconstruct its glacial history. It is probable, therefore, that in the Alps, as in northern Europe, resident genotypes surviving glaciation in situ were integrated into the gene pool of postglacially immigrating periglacial individuals. The size of refugia differed according to species and region. On the one hand, refugia were restricted to individual mountains (E. alpinus, R. nivalis). On the other hand, they spanned several mountain ranges in larger areas (E. nanum, E. alpinus). Postglacial migration over longer distances was inferred for E. alpinus from southern France to northern Switzerland, and, over shorter distances, for R. nivalis from the northern Prealps into the Central Alps in Switzerland. Both postglacial immigration and in situ survival shaped the phylogeography at least of E. alpinus and R. nivalis. It is likely, therefore, that the nunatak and the tabula rasa hypotheses are too simplistic to describe the rich diversity of glacial and postglacial processes in Alpine plant species. It rather appears that the glacial history of each species is to a certain degree unique and influenced by its ecological demands or breeding systems. Moreover, stochasticity has to be regarded of essential importance, since factors such as preglacial distribution patterns or postglacial dispersal or extinction events should have had effects on the present genetic composition and the distribution of a species.

The proximity of mates can influence mating opportunities and the quantity and quality of offspring, especially in dioecious plant species. Progeny sex ratios modulated by environmental conditions is one of the most radical ways in which offspring quality may be influenced, yet it has rarely been reported in plants. A mechanism proposed to influence progeny sex ratios in dioecious plants involves competition between female-and male-determining microgametophytes (certation) as a result of variation in pollination intensity. However, the role of selective fertilization in dioecious plants is controversial and has not been demonstrated under field conditions. Here we investigate whether natural variation in the spatial arrangement of females and males influences pollination intensity and progeny sex ratios in the wind-pollinated herb Rumex nivalis. Based on previous experimental manipulation of pollination intensity in this species, we predicted that maternal parents in close proximity to males would produce more strongly female-biased progeny sex ratios. We tested this prediction in six alpine populations in Switzerland by measuring the distance between focal females and neighboring males and assessing pollen loads and seed sex ratios of maternal parents. In four of the six populations, females positioned in close proximity to males captured more pollen and exhibited more female-biased sex ratios. Our results demonstrate that demographic aspects of the maternal mating environment can influence progeny sex ratios. The most probable explanation for biased primary sex ratios in Rumex is selective fertilization resulting from pollen tube competition.female-biased sex ratios ͉ pollination intensity ͉ selective fertilization T he spatial context in which reproduction occurs is of critical importance for plants because of their sessile habit. Most plants mate and disperse offspring locally, so that mating success is context-dependent and influenced by plant density and the phenotypic composition of neighborhoods (1-3). Dioecious species are especially sensitive to spatial structure and composition because of the restricted number of mating groups within populations. Female reproductive success can be influenced by male flowering density, depending on the extent of pollen dispersal (4-6). Patch density and the local sex ratio may also affect parental fitness through their influence on pollination intensity. The amount of pollen captured by stigmas could potentially affect both the quality of offspring and progeny sex ratios through gametophytic competition (certation) and selective fertilization (7,8). However, the relative roles of genetic and environmental factors in governing primary sex ratios in dioecious populations are still poorly understood, and evidence for environmentally induced variation in primary sex ratios is limited despite considerable heterogeneity in seed sex ratios (9).Sex determination induced by the environment is one of the most direct ways in which progeny sex ratios can vary. Environmental sex de...

The glacial history of the alpine herb Rumex nivalis was investigated using amplified fragment length polymorphisms (AFLPs) and restriction fragment length polymorphisms with polymerase chain reaction (PCR-RFLPs) of cpDNA. Both traditional statistical methods widely applied in phylogeographic research and nested clade analysis were used. The AFLPs indicated little geographic structure probably due to the wind-pollinated reproductive system of the dioecious R. nivalis. Because cpDNA haplotypes exhibited distinct distributional patterns, correlation between AFLPs and PCR-RFLPs was low. The results of common statistical methods and of nested clade analysis were largely congruent. Both supported in situ survival of one group of common haplotypes in the Central Alps. For another group of common haplotypes, classical phylogeographic analyses gave strong evidence for survival in peripheral refugia at the northern alpine border, whereas this conclusion was not as clearly supported in the nested clade analysis. Nested clade analysis provided several detailed insights on past and ongoing populational demographic processes. Thus, it is a valuable tool in the phylogeographical analysis of haplotype data, but it should preferably be combined with other statistical analyses. In situations with low genetic variation in cpDNA, classical phylogeographic analytical tools on nuclear DNA will still be the methods of choice.