AimTo understand global patterns of genetic variation in plant species on mountains and to consider the significance of mountains for the genetic structure and evolution of plant species.Location Global. MethodsWe review published studies.Results Genetic diversity within populations can vary along altitudinal gradients in one of four patterns. Eleven of 42 cited studies (26% of the total) found that populations at intermediate altitudes have greater diversity than populations at lower and higher altitudes. This is because the geographically central populations are under optimal environmental conditions, whereas the peripheral populations are in suboptimal situations. The second pattern, indicating that higher populations have less diversity than lower populations, was found in eight studies (19%). The third pattern, indicating that lower populations have lower diversity than higher populations, was found in 10 studies (24%). In 12 studies (29%), the intrapopulation genetic variation was found to be unaffected by altitude. Evidence of altitudinal differentiation was found in more than half of these studies, based on measurements of a range of variables including genome size, number of chromosomes or a range of loci using molecular markers. Furthermore, great variation has been found in phenotypes among populations at different altitudes in situ and in common garden experiments, even in cases where there was no associated variation in molecular composition. Mountains can be genetic barriers for species that are distributed at low elevations, but they can also provide pathways for species that occupy high-elevation habitats.[Correction added after publication 9 October 2007: 'less diversity' changed to 'greater diversity' in the second sentence of the Results section of the Abstract].Main conclusions Genetic diversity within populations can vary along altitudinal gradients as a result of several factors. The results highlight the importance of phenotypic examinations in detecting altitudinal differences. The influence of mountain ridges on genetic differentiation varies depending, inter alia , on the elevation at which the species occurs. Based on these findings, zoning by altitudes or ridges would be helpful for the conservation of tree populations with the onset of global warming.

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Previous studies have reached different discussions about the genetic variation and genetic structure of Quercus crispula populations in northeastern Japan. This is a common oak species in Eastern Asia. Some studies have suggested that the populations in northeastern Japan were derived from those remaining in the southwest after the last glacial maximum (LGM), whilst other studies have found evidence that populations persisted in northeastern Japan during the LGM. Using seven highly polymorphic nuclear simple sequence repeat loci, we investigated the genetic structure of 16 Q. crispula populations along a latitudinal gradient in northeastern Japan (northern Honshu and Hokkaido), spanning about half of the species' biogeographic range in the country. Although the level of population differentiation was low (F (ST) = 0.021; [Formula: see text] = 0.090), two geographically differentiated clusters were detected by STRUCTURE analysis. The first cluster included most of the populations in Hokkaido, and may indicate continued survival throughout past glacial periods. We found a significant decrease in allelic richness with latitude, so the second cluster may represent an expansion of the lineage from Honshu during the post-glacial period. These results should enhance our understanding of historical north-south migrations of this species in northeastern Japan.

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As a result of ecological and historical factors, plant species occurring in mountainous regions often exhibit complex phylogeographical structure. The aim of this review is to identify the main phylogeographic patterns of plant species in the Japanese Archipelago, based on 63 previous studies; in particular, the intention is to examine the effects of mountains on these patterns. We classified species into three groups based on their distribution along altitudinal gradients: alpine and sub-alpine; montane; and lowland plants. Identified patterns were diverse, but we found particular ecological/historical constraints influencing the distribution of intra-population variation and contributing to clear genetic differentiation in alpine and sub-alpine and montane species. Many alpine and subalpine species harbored greater variation in the highlands of central Japan, and this was the case for dominant montane species in central and western Japan. These areas are considered to have acted as refugia during the last glacial maximum. Some other highland species even survived in small refugia in northern Japan. Genetic differentiation was regularly found between either side of 38°N latitude, between the Japan Sea and the Pacific Ocean sides of the country and on either side of the Itoiga-Shizuoka Tectonic Line. Unexpectedly, strong structure has rarely been found in lowland species. Based on the observed patterns, we discuss possible reasons for the discrepancies among phylogeographical structures of different species within the same groups. In addition, the phylogeographical patterns detected are compared with floristic structures described in classical biogeographical terms.

We evaluated the genetic structure of 16 Betula maximowicziana populations in the Chichibu mountain range, central Japan, located within a 25-km radius; all but two populations were at altitudes of 1,100-1,400 m. The results indicate the effects of geographic topology on the landscape genetic structure of the populations and should facilitate the development of local-scale strategies to conserve and manage them. Analyses involving 11 nuclear simple sequence repeat loci showed that most populations had similar intrapopulation genetic diversity parameters. Population differentiation (F ST =0.021, G′ ST =0.033) parameters for the populations examined were low but were relatively high compared to those obtained in a previous study covering populations in a much larger area with a radius of approximately 1,000 km (F ST =0.062, G′ ST = 0.102). Three populations (Iriyama, Kanayamasawa, and Nishizawa) were differentiated from the other populations by Monmonier's and spatial analysis of molecular variance algorithms or by STRUCTURE analysis. Since a high mountain ridge (nearly 2,000 m) separates the Kanayamasawa and Nishizawa populations from the other 14 populations and the Kanayamasawa and Nishizawa populations are themselves separated by another mountain ridge, the genetic structure appears to be partly due to mountain ridges acting as genetic barriers and restricting gene flow. However, the Iriyama population is genetically different but not separated by any clear geographic barrier. These results show that the landscape genetic structure is complex in the mountain range and we need to pay attention, within landscape genetic studies and conservation programs, to geographic barriers and local population differentiation.

-The seed dispersal patterns and genetic structure of plant populations in mountainous forests may differ from those on flat sites, because some seeds that fall from adults are likely to roll downhill, and thus cause the seed shadows from different mother trees to merge. In the study reported here we used six polymorphic microsatellite markers to track seed dispersal and examine the fine-scale spatial genetic structure of adults and first-year seedlings of Quercus crispula in 2500 m 2 plots on four slopes. In each of the four plots, leaves of adults, seedlings and endocarps of hypogeal cotyledons attached to the seedlings were genotyped to identify the seedlings' mother trees. The results showed that steeper slopes result in larger dispersions and smaller genetic structure of seedlings. These findings are a crucial step towards an understanding of the effect of topography on tree regeneration. genetic structure / microsatellite marker / Quercus crispula / seed dispersal / slope Résumé -Influence des pentes fortes sur la dispersion et la structure génétique des populations de Quercus crispula. Les modes de dispersion des graines et la structure génétique des populations d'arbres peuvent être différents en forêts de montagne par rapport à ceux en forêts de plaine. En effet, les graines qui tombent des arbres adultes roulent probablement vers le bas de la pente entraînant un regroupement des descendances de différentes mères. Dans cette étude, nous avons suivi la dispersion des graines de Quercus crispula et nous avons examiné à l'aide de six marqueurs microsatellites polymorphiques la structure spatiale génétique des arbres adultes et de leurs descendants (semis de 1 an) sur des placeaux de 2500 m 2 dans quatre pentes. Dans chacun des placeaux, les feuilles des arbres adultes et des semis ainsi que les endocarpes des cotylédons attachés aux semis ont été génotypés de manière à identifier les mères des semis. Les résultats montrent que les pentes fortes contribuent à une forte dispersion et à une faible structuration génétique des semis. Ces résultats sont une étape importante pour la compréhension des effets de la topographie sur la régénération des arbres. structure génétique / marqueur microsatellite / Quercus crispula / dispersion des graines / pente

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