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Habitat fragmentation and small population size can lead to genetic erosion in threatened plant populations. Classical theory implies that dioecy can counteract genetic erosion as it decreases the magnitude of inbreeding and genetic drift due to obligate outcrossing. However, in small populations, sex ratios may be strongly male- or female-biased, leading to substantial reductions in effective population size. This may theoretically result in a unimodal relationship between sex ratios and genetic diversity; yet, empirical studies on this relationship are scarce. Using AFLP markers, we studied genetic diversity, structure and differentiation in 14 highly fragmented Antennaria dioica populations from the Central European lowlands. Our analyses focused on the relationship between sex ratio, population size and genetic diversity. Although most populations were small (mean: 35.5 patches), genetic diversity was moderately high. We found evidence for isolation-by-distance, but overall differentiation of the populations was rather weak. Females dominated 11 populations, which overall resulted in a slightly female-biased sex ratio (61.5%). There was no significant relationship between population size and genetic diversity. The proportion of females was not unimodally but positively linearly related to genetic diversity. The high genetic diversity and low genetic differentiation suggest that A. dioica has been widely distributed in the Central European lowlands in the past, while fragmentation occurred only in the last decades. Sex ratio has more immediate consequences on genetic diversity than population size. An increasing proportion of females can increase genetic diversity in dioecious plants, probably due to a higher amount of sexual reproduction., (© 2018 German Society for Plant Sciences and The Royal Botanical Society of the Netherlands.)

Environmental gradients, and particularly climatic variables, exert a strong influence on plant distribution and, potentially, population genetic diversity and differentiation. Differences in water availability can cause among-population variation in ecological processes and can thus interrupt populations' connectivity and isolate them environmentally. The present study examines the effect of environmental heterogeneity on plant populations due to environmental isolation unrelated to geographic distance. Using AFLP markers, we analyzed genetic diversity and differentiation among 12 Salvia spinosa populations and 13 Salvia syriaca populations from three phytogeographical regions (Mediterranean, Irano-Turanian and Saharo-Arabian) representing the extent of the species' geographic range in Jordan. Differences in geographic location and climate were considered in the analyses. For both species, flowering phenology varied among populations and regions. Irano-Turanian and Saharo-Arabian populations had higher genetic diversity than Mediterranean populations, and genetic diversity increased significantly with increasing temperature. Genetic diversity in Salvia syriaca was affected by population size, while genetic diversity responded to drought in S. spinosa. For both species, high levels of genetic differentiation were found as well as two well-supported phytogeographical groups of populations, with Mediterranean populations clustering in one group and the Irano-Turanian and Saharo-Arabian populations in another. Genetic distance was significantly correlated to environmental distance, but not to geographic distance. Our data indicate that populations from moist vs. arid environments are environmentally isolated, where environmental gradients affect their flowering phenology, limit gene flow and shape their genetic structure. We conclude that environmental heterogeneity may act as driver for the observed variation in genetic diversity., (© 2016 German Botanical Society and The Royal Botanical Society of the Netherlands.)

Genetic diversity is important for species' fitness and evolutionary processes but our knowledge on how it varies across a species' distribution range is limited. The abundant centre hypothesis (ACH) predicts that populations become smaller and more isolated towards the geographic range periphery - a pattern that in turn should be associated with decreasing genetic diversity and increasing genetic differentiation. We tested this hypothesis in Adonis vernalis, a dry grassland plant with an extensive Eurasian distribution. Its life-history traits and distribution characteristics suggest a low genetic diversity that decreases and a high genetic differentiation that increases towards the range edge. We analysed AFLP fingerprints in 28 populations along a 4698-km transect from the geographic range core in Russia to the western range periphery in Central and Western Europe. Contrary to our expectation, our analysis revealed high genetic diversity (range of proportion of polymorphic bands = 56-81%, He = 0.168-0.238) and low genetic differentiation across populations (Φ(ST) = 0.18). However, in congruence with the genetic predictions of the ACH, genetic diversity decreased and genetic differentiation increased towards the range periphery. Spanish populations were genetically distinct, suggesting a divergent post-glacial history in this region. The high genetic diversity and low genetic differentiation in the remaining A. vernalis populations is surprising given the species' life-history traits and points to the possibility that the species has been widely distributed in the studied region or that it has migrated from a diverse source in an East-West direction, in the past., (© 2015 German Botanical Society and The Royal Botanical Society of the Netherlands.)

Premise of the Study: Biological responses to climatic change usually leave imprints on the genetic diversity and structure of plants. Information on the current genetic diversity and structure of dominant tree species has facilitated our general understanding of phylogeographical patterns., Methods: Using amplified fragment length polymorphism (AFLPs), we compared genetic diversity and structure of 384 adults of P. tarapacana with those of 384 seedlings across 32 forest sites spanning a latitudinal gradient of 600 km occurring between 4100 m and 5000 m a.s.l. in Polylepis tarapacana (Rosaceae), one of the world's highest treeline species endemic to the central Andes., Key Results: Moderate to high levels of genetic diversity and low genetic differentiation were detected in both adults and seedlings, with levels of genetic diversity and differentiation being almost identical. Four slightly genetically divergent clusters were identified that accorded to differing geographical regions. Genetic diversity decreased from south to north and with increasing precipitation for adults and seedlings, but there was no relationship to elevation., Conclusions: Our study shows that, unlike the case for other Andean treeline species, recent human activities have not affected the genetic structure of P. tarapacana, possibly because its inhospitable habitat is unsuitable for agriculture. The current genetic pattern of P. tarapacana points to a historically more widespread distribution at lower altitudes, which allowed considerable gene flow possibly during the glacial periods of the Pleistocene epoch, and also suggests that the northern Argentinean Andes may have served as a refugium for historical populations., (© 2015 Botanical Society of America.)

Premise of the Study: Central European salt habitats are mainly restricted to the maritime coast but scattered occurrences can also be found inland. In inland habitats, human activities have caused losses and reductions in the size of natural salt sites but have also created new anthropogenic habitats around potash mining dumps colonized by halophytic species in the last 30 yr. We aimed to investigate the effects of bottlenecks, isolation, and ongoing habitat fragmentation on the genetic variation of a species commonly growing in these special habitats., Methods: We used 10 microsatellite markers to compare genetic diversity and differentiation of 31 populations of Suaeda maritima (Chenopodiaceae) from Central European coasts and inland habitats. Two approaches were applied to analyze the tetraploid data based on allele frequencies directly derived from microsatellite data and from transformed binary data., Key Results: In comparison to the coastal populations from the North Sea and the English Channel, significantly reduced genetic variation and increased between-population differentiation was revealed for populations from the German inland and the Baltic Sea coast. Genetic structure analyses clearly separated coastal and inland populations., Conclusions: Our results indicate that gene flow is restricted among populations from inland salt sites and the Baltic Sea coast, presumably due to their isolation, small sizes, genetic bottlenecks and/or founder events. Patterns of allele distribution indicate some occasional genetic exchange among habitat types in the past. Anthropogenic salt sites may facilitate gene flow among inland salt habitats preventing endangered inland halophyte populations from genetic erosion.

Premise of the Study: The role of pollen flow within and between cultivated and wild tropical crop species is little known. To study the pollen flow of cacao, we estimated the degree of self-pollination and pollen dispersal distances as well as gene flow between wild and cultivated cacao (Theobroma cacao L.)., Methods: We studied pollen flow and genetic diversity of cultivated and wild cacao populations by genotyping 143 wild and 86 cultivated mature plants and 374 seedlings raised from 19 wild and 25 cultivated trees at nine microsatellite loci., Key Results: A principal component analysis distinguished wild and cultivated cacao trees, supporting the notion that Bolivia harbors truly wild cacao populations. Cultivated cacao had a higher level of genetic diversity than wild cacao, presumably reflecting the varied origin of cultivated plants. Both cacao types had high outcrossing rates, but the paternity analysis revealed 7-14% self-pollination in wild and cultivated cacao. Despite the tiny size of the pollinators, pollen was transported distances up to 3 km; wild cacao showed longer distances (mean = 922 m) than cultivated cacao (826 m). Our data revealed that 16-20% of pollination events occurred between cultivated and wild populations., Conclusions: We found evidence of self-pollination in both wild and cultivated cacao. Pollination distances are larger than those typically reported in tropical understory tree species. The relatively high pollen exchange from cultivated to wild cacao compromises genetic identity of wild populations, calling for the protection of extensive natural forest tracts to protect wild cacao in Bolivia.

Worldwide, botanical gardens cultivate around 80,000 taxa, corresponding to approximately one-quarter of all vascular plants. Most cultivated taxa are, however, held in a small number of collections, and mostly only in small populations. Lack of genetic exchange and stochastic processes in small populations make them susceptible to detrimental genetic effects, which should be most severe in annual species, as sowing cycles are often short. In order to assess whether ex situ cultivation affects genetic diversity of annuals, five annual arable species with similar breeding systems were assessed with 42 in situ populations being compared to 20 ex situ populations using a random amplified polymorphic DNA (RAPD) analysis approach. Population sizes tended to be lower under ex situ cultivation and levels of genetic diversity also tended to be lower in four of the five species, with differences being significant in only two. Ex situ populations showed incomplete representation of alleles found in the wild. The duration of cultivation did not indicate any effect on genetic diversity. This implies that cultivation strategies resulted in different genetic structures in the garden populations. Although not unequivocally pronounced, differences nonetheless imply that conservation strategies in the involved gardens may need improvement. One option is cold storage of seeds, a practice that is not currently followed in the studied ex situ collections. This may reflect that the respective gardens focus on displaying living plant populations., (© 2012 German Botanical Society and The Royal Botanical Society of the Netherlands.)

Premise of the Study: Knowledge on the range-wide distribution of genetic structure and diversity is required to facilitate the understanding of historical tree migration and for predicting responses to current climate change. With respect to post-glacial migration patterns known from the northern hemisphere, we tested the prediction that the southernmost populations of a subtropical tree line species have lower within-population genetic diversity and higher genetic differentiation than the central and northernmost populations., Methods: We used AFLP to assess the genetic structure of 18 populations of the wind-pollinated Polylepis australis (Rosaceae) sampled over its entire distributional range in three Argentinean high mountain regions. Genetic diversity was calculated as a percentage of polymorphic bands (P) and Nei's expected heterozygosity (He); genetic differentiation was assessed using AMOVA, Φ(ST)--statistics, and Bayesian cluster analysis., Key Results: Contrary to our expectations, the northernmost Polylepis australis stands had lower within-population genetic diversity and higher genetic differentiation than the central and southernmost stands. Populations grouped into two major clusters, the first containing the southern populations and four central populations and the second containing the northern and one central population., Conclusions: Patterns of Polylepis australis genetic structure and diversity differ from historical migration scenarios observed for the northern hemisphere. The decline in genetic diversity toward the north may point to an equatorward migration following past climatic changes. Populations within the south and central part appear to be connected by effective long-distance pollination while gene flow in the northern part is probably hampered by geographic isolation.

Premise of the Study: Intraspecific genetic variation is essential for the performance and evolution of species. Populations at a species' geographic range periphery receive considerable attention in biogeography and conservation because they are smaller and spatially more isolated than central populations, a pattern expected to lead to higher genetic differentiation and lower within-population genetic diversity. We tested these predictions in central and peripheral populations of the Eurasian steppe grass Stipa capillata., Methods: We analyzed AFLP fingerprint patterns in 319 individuals from 20 large and abundant populations in the core, in Kazakhstan, and 23 small and isolated populations at the periphery, in Central Europe. We calculated different genetic diversity estimates and assessed genetic differentiation among populations by examining F(ST) values, a neighbor-net network, and an AMOVA., Key Results: As expected, genetic differentiation among populations was significantly larger at the range periphery (F(ST) = 0.415) than in the range core (F(ST) = 0.164). In contrast to predictions, however, we found similarly low genetic diversity within central (proportion of polymorphic bands = 21.9%) and peripheral (20%) populations., Conclusions: Higher genetic differentiation in the small and spatially isolated peripheral populations is likely driven by genetic drift and reduced gene flow due to a complex landscape structure and the abandonment of traditional management regimes. With regard to unchanged genetic diversity, it appears that life-history traits like longevity or sufficiently large population sizes could allow S. capillata to escape deleterious effects at the range edge.

Stipa capillata L. (Poaceae) is a rare grassland species in Central Europe that is thought to have once been widespread in post-glacial times. Such relict species are expected to show low genetic diversity within populations and high genetic differentiation between populations due to bottlenecks, long-term isolation and ongoing habitat fragmentation. These patterns should be particularly pronounced in selfing species. We analysed patterns of random amplified polymorphic DNA (RAPD) variation in the facultatively cleistogamous S. capillata to examine whether genetic diversity is associated with population size, and to draw initial conclusions on the migration history of this species in Central Europe. We analysed 31 S. capillata populations distributed in northeastern, central and western Germany, Switzerland and Slovakia. Estimates of genetic diversity at the population level were low and not related to population size. Among all populations, extraordinarily high levels of genetic differentiation (amova: phi(ST) = 0.86; Bayesian analysis: theta(B) = 0.758) and isolation-by-distance were detected. Hierarchical amova indicated that most of the variability was partitioned among geographic regions (59%), or among populations between regions when the genetically distinct Slovakian populations were excluded. These findings are supported by results of a multivariate ordination analysis. We also found two different groups in an UPGMA cluster analysis: one that contained the populations from Slovakia, and the other that combined the populations from Germany and Switzerland. Our findings imply that S. capillata is indeed a relict species that experienced strong bottlenecks in Central Europe, enhanced by isolation and selfing. Most likely, populations in Slovakia were not the main genetic source for the post-glacial colonization of Central Europe.

Calamagrostis pseudopurpurea is one of only a few endemic species in Germany and is confined to the catchment area of the River Mulde in the states of Saxony and Saxony-Anhalt. We studied the genetic structure and seed viability across its entire distribution area. Patterns of random amplified polymorphic DNA (RAPD) variation were analysed using 183 individuals from 43 stands in order to assess the overall genetic structure and the extent of clonality. In addition, four related Calamagrostis species (C. canescens, C. epigejos, C. phragmitoides and C. villosa) were included in our study to consider the probable phylogenetic origin of C. pseudopurpurea. We detected two clearly different RAPD phenotypes of C. pseudopurpurea, each distributed along the river banks of two spatially isolated stream courses. Both phenotypes are present downstream of the confluence. Our results indicate that C. pseudopurpurea originates from two distinct periods of hybridisation between the same parental taxa, and that clonal propagation is most likely the main reproduction method. In line with its hybrid origin, embryos of sampled C. pseudopurpurea caryopses were found to be mostly degraded or unviable over several years. Calamagrostis pseudopurpurea is genetically closer to C. canescens and C. phragmitoides than it is to other studied species, but C. canescens and C. phragmitoides have not been proven to be direct parental taxa of C. pseudopurpurea. Calamagrostis pseudopurpurea should therefore still be treated as a separate species that needs special attention from a conservation point of view.