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Fragmentation and environmental constraints influence genetic diversity and germination of Stipa pennata in natural steppes
Abstract
Human impact and fragmentation often have negative effects on plant population sizes. This can lead to declining genetic diversity due to restricted gene flow and genetic bottlenecks, and eventually result in reduced reproductive fitness. Environmental conditions can also influence the genetic structure of populations and directly affect their reproduction success.
For _Stipa pennata_, the key species of largely natural steppes in southern Siberia, using AFLP we tested whether genetic variability and germination are negatively influenced by fragmentation, and assessed the influence of local environmental conditions. Genetic diversity was moderately high (mean percentage of polymorphic bands = 38.4%), with high genetic differentiation occurring between populations (ΦST = 0.547). Genetic variation was mainly partitioned (41.8%) between two distinct grassland types. Isolation negatively affected genetic diversity, highlighting that fragmentation had an impact on genetic structure. Higher mean precipitation negatively influenced population size, population density and genetic diversity. The speed of seed germination was correlated positively with population size and negatively with vegetation cover, while we found no evidence for negative effects of low genetic diversity on percentage of seed germination. The presence of different genetic groups shows that populations have adapted to a range of environments. Germination speed also differed between groups, as a consequence of maternal effects or of adaption to certain environmental conditions.
Our results show that fragmentation can have potentially strong effects even in natural grasslands. We recommend that any future restoration schemes take the observed pronounced genetic differentiation into account.
... Thus, conservation genetic studies are urgently needed to improve locally adapted restoration measures. One of the few population genetic studies in Middle Asia was conducted on the characteristic Eurasian steppe grass Stipa pennata in the South Siberian Kulunda steppe (Heinicke et al., 2016). This study revealed clear signs of genetic depletion in spatially isolated populations and found strong genetic differentiation between two distinct vegetation types. ...
... Our study area, the north-western part of the Kulunda Steppe, is located in the semi-arid foreland of the Altai Mountains (Altay Krai, South Siberia; Fig. 1A). Precipitation decreases from the wetter North-East towards the South-West resulting in a pronounced vegetation gradient from forest steppes in the North-East to more typical steppes and to dry steppes in the South-West (Heinicke et al., 2016). The Kulunda steppe is a bona fide model to study the effects of recent fragmentation as it is a typical example for the largescale conversion of temperate grasslands: in the course of the soviet Virgin Lands Campaign, more than 80% of natural steppes were transformed into intensively used cropland, rendering many native steppe species threatened (Aleksandrova et al., 2006). ...
... As such, the most isolated population J1 showed a clear separation from all other populations in the STRUCTURE analysis, whereas we did not find such clear patterns in the STRUC-TURE analyses of A. villosa and P. hybrida. The only other AFLP study in the Kulunda steppe so far revealed high genetic differentiation in S. pennata (Heinicke et al., 2016). The mating system of that species is, however, dominated by cleistogamy, which may account for these findings. ...
Habitat fragmentation can lead to substantial genetic depletion. As a consequence, restoration schemes often involve the introduction of propagules into isolated plant populations to improve genetic diversity. To avoid introducing maladapted seed material, such measures need to account for landscape genetic processes. However, surprisingly little is known as to whether different species within a distinct fragmented ecosystem respond similarly or idiosyncratically to eco-geographical variation.
Using AFLP markers, we studied the population genetic structure in three species of the highly fragmented Kulunda steppe (South Siberia): Adonis villosa, Jurinea multiflora and Paeonia hybrida. In each population, we conducted a vegetation survey. We performed Mantel tests and an RDA approach to investigate how genetic structure was affected by three spatio-environmental variables: spatial distance, floristic composition and climate.
Despite strong fragmentation, genetic diversity was moderate (A. villosa, J. multiflora) to high (P. hybrida), while differentiation was weak (A. villosa) to moderate (P. hybrida, J. multiflora). Mantel tests showed that spatial distance correlated with genetic distance in A. villosa and P. hybrida. Floristic composition was significantly associated with genetic differentiation in A. villosa. Climate did not have an effect on genetic structure in any species.
All three species are long-lived, which may contribute to explaining why genetic effects of recent fragmentation are still limited. We highlight that floristic composition can be a powerful predictor of population differentiation in species that show rather stable conditions in their recent population histories (e.g. A. villosa). This can have important implications for identifying source populations where restoration actions involve the (re)introduction of propagules. In contrast, for P. hybrida and J. multiflora, we could not identify deterministic drivers of differentiation. We advocate that future studies should aim at disentangling the interactive effects of varying life cycles, eco-evolutionary population histories and spatio-environmental heterogeneity in fragmented landscapes.
... This marvelous plant does not grow in Romania. Still, there grows another member of the same plant family, Stipa pennata, that grows in a broad area from the Eastern European steppes to Central Europe [15]. Stipa pennata fiber has a feather-like structure very similar to Stipa tenacissima, with a long stem with lateral bristles, which one expects to act as microstructural anchors within the slurry compacts, generating a reinforcing network. ...
... This marvelous natural fiber is obtained from Stipa tenacissima, which is commonly found in Southern Spain and Northern Africa (Tunisia and Morocco) [14]. Unfortunately, it did not grow in Romania, but another similar plant, Stipa pennata, grows spontaneously on the slope of hills from the Eastern European steppes to Central Europe [15]. It grows abundantly on the slope of the hills in Romania, can be easily collected, and has no agricultural usage. ...
Background: ceramic tile wastewater slurry contains a large amount of fine kaolinite particles acting as a matrix for mineral filler particles of quartz and mullite. Reinforcing it with natural fibers increases its compression strength. A novel approach is using Stipa pennata fibers because of their local availability, good mechanical properties, and feathery aspect, making them able to reinforce ceramic slurry compacts. Preparation and investigation methods: Slurry conditioned at 33% humidity and milled at 6000 rpm for 5 min contains 39% quartz, 37% kaolinite, 16% mullite and 8% lepidocrocite (observed via XRD correlated with mineralogical microscopy). Kaolinite particles ensure optimal binding of the mineral filler and the Stipa pennata fibers into a dense composite structure, as observed via SEM. EDS maps reveal a local increase in C content, along with the natural fibers being associated with significant levels of Al and Si, indicating the microstructural compactness of the reinforcement layer. An additional compaction load enhances microstructural cohesion. Results: The sample without reinforcement has a compressive strength of 1.29 MPa. This increases to 2.89 MPa by adding a median reinforcing layer and reaches 3.13 MPa by adding a compaction load of 20 N. A median crossed fiber-reinforcing layer combined with the compaction load of 20 N ensures a compressive strength of 4.78 MPa. Introducing two reinforcing layers oriented perpendicular to one another ensures a compressive strength of 2.48 MPa. Lateral placement of the two reinforcing layers regarding the sample median plan causes a slight decrease in the compressive strength. SEM fractography reveals that the feather-like structure of Stipa pennata fiber acts as an anchor for the median site of the samples, slowing crack initiation under compressive efforts, creating a novel approach compared to natural fiber without lateral flakes. Conclusions: The optimal place for the reinforcement layer is the median site of the sample, and interlaced reinforcement ensures the best compressive resistance. Ceramic slurry reinforced with Stipa pennata is useful as an intermediary layer on the modular walls of ecologic buildings.
... Other studies relate fitness measured as germination success, among other parameters, to genetic diversity (Greimler and Dobeš, 2000;Ali et al., 2006;Crawford and Whitney, 2010;González-Varo et al., 2010;. Nevertheless, some authors report that seed responses are more related to environmental aspects than to genetic diversity (Heinicke et al., 2016;Rodríguez-Rodríguez et al., 2018), which might be mediated by epigenetic processes (Zhang and Ogas, 2009), whereas some specific genes have been associated with germination success in stressful environments (Liu et al., 2020;Rehman et al., 2020). ...
... However, these intrinsic features do not seem to be clearly related to germination responses. Genetic diversity does not seem to affect the current germination success herein determined and similar results have been obtained in other plants, such as Sambucus palmerensis (Rodríguez-Rodríguez et al., 2018), Stippa pennata (Heinicke et al., 2016), among others. Likewise, the phylogenetic characterization shows a clear split into two species, as Biondi et al. (2013) concluded using morphologic data, which cannot be associated with germination strategies. ...
Reproductive strategies for specific populations are closely related to environmental factors. Consequently, they are fundamental for conservation plans and the management of threatened habitats like salt marshes. From this viewpoint, germination strategy under different temperatures and salt conditions, voltammetric parameters and molecular analysis were performed and compared in six Halocnemum populations (four of H. cruciatum and two of H. strobilaceum ) growing on Mediterranean (Balearic, Tyrrenic and Adriatic) and Red Sea coasts to establish the relation to environmental variables. Significant interpopulation differences were found in all the evaluated parameters. The Mediterranean populations showed a variable opportunistic germination strategy that was directly related to the drought period length at the studied sites. Consequently, potential environmental predictors of seed response were identified. The most noteworthy were bioclimate, soil texture, continentality index, winter temperatures and summer precipitations. Additionally, voltammetric parameters were evidenced as indicators of maternal plant stress levels and, thus, as potential determinants of future seed responses. The phylogenetic analyses showed a split into two species that did not correspond to germination response. The phylogeographic analyses showed interpopulation differences in haplotype composition for H. cruciatum , but not for H. strobilaceum . In conclusion, the tight connection between seed responses and the ecological parameters of natural populations as an adaptation for successful seedling emergence was proved regardless of its phylogenetic relations.
... Other studies were focussed on smaller western or eastern parts of the Eurasian steppe belt (e.g. Hensen et al., 2010;Spaniel et al., 2011;Heinicke et al., 2016;Kajtoch et al., 2016;Meindl et al., 2016;Plenk et al., 2017;Rosche et al., 2018). Although some general patterns, like longitudinal, likely glacial-induced range splits and/or east-west genetic diversity gradients have been revealed, our knowledge is far from giving an overarching picture of the biogeographical history of characteristic steppe species (groups). ...
... Although some general patterns, like longitudinal, likely glacial-induced range splits and/or east-west genetic diversity gradients have been revealed, our knowledge is far from giving an overarching picture of the biogeographical history of characteristic steppe species (groups). More rarely, also fitness parameters of steppe plant populations were investigated in combination to genetic data, like in Stipa capillata (Wagner et al., 2011b;Heinicke et al., 2016) or Poa badensis (Plenk et al., 2019a), mostly indicating independence of germination rates from genetic diversity patterns. Moreover, some studies examined the biogeographical history of whole steppe plant groups diversifying within the Eurasian steppe system, like the genera Dontostemon and Clausia (Friesen et al., 2016), demonstrating the evolutionary potential within the Eurasian steppe biome. ...
Hypotheses of peripherality have characterised peripheral populations by increasing population differentiation and by declining genetic diversity towards the absolute range edge. However, such biogeographical patterns are not generally confirmed. Moreover, it was recently argued that lower levels of genetic diversity at the western and eastern periphery of the Eurasian steppe belt are only detectable by full-range longitudinal sampling. To uncover common genetic patterns of Central European steppe plants we here investigated Adonis vernalis populations across a transect towards their (north)westernmost range edge. Our study species shows a disjunct peripheral distribution with common Pannonian (Central Hungary) and more eastern occurrences (Romanian Dobruja) compared to the western edge of their continuous Pannonian range (Eastern Austria) and (north)westernmost isolated exclaves (Western Germany).
We analysed 3–5 populations from each of these four study regions by cpDNA sequence (atpI-atpH, rpL16 intron) and AFLP fragment variation. Our AFLP results, based on 323 individuals, showed strong population differentiation, most pronounced within the Hungarian Pannonicum. Moreover, AFLP variation indicated high genetic diversity in the German exclave and at the Pannonian range edge in Eastern Austria compared to less peripheral, more eastern populations. While AFLP results are opposed to theoretical expectations, cpDNA data (i.e. 12 haplotypes) demonstrated lower haplotype diversity towards the (north)westernmost exclave and no monomorphic population within the Romanian Dobruja. Therefore, the latter marker complies with the peri-pheral transect predictions, although no material from Asia was included. Hence, not only the geographical scale is of importance when analysing phylogeographical patterns, but also possible differences of genetic marker systems. Showing strong signals of recent bottlenecks based on cpDNA in the German exclave, the biogeographical history of A. vernalis somehow differs from other steppe plants investigated to date across the same peripheral transect.
... As steppe originally covered vast continuous areas, steppe plants might not be adapted to fragmentation . However, there have only been few publications on the impact of fragmentation on the genetic structure of plant populations in natural steppes (Heinicke et al. 2016;Wódkiewicz, Dembicz, & Moysiyenko 2016;Parnikoza et al. 2017). Fragmentation lowered the genetic diversity of the self-compatible, wind-pollinated and anemochorous Stipa pennata (Heinicke et al. 2016). ...
... However, there have only been few publications on the impact of fragmentation on the genetic structure of plant populations in natural steppes (Heinicke et al. 2016;Wódkiewicz, Dembicz, & Moysiyenko 2016;Parnikoza et al. 2017). Fragmentation lowered the genetic diversity of the self-compatible, wind-pollinated and anemochorous Stipa pennata (Heinicke et al. 2016). The first signs of genetic drift have also been observed in Stipa capillata populations from Southern Ukrainian kurgans (Wódkiewicz et al. 2016). ...
Habitat fragmentation can prevent gene flow between plant populations and lead to a loss of genetic diversity. However, such impact of fragmentation has not always been consistently confirmed by previous studies and the issue still needs further research. Particularly little is known about the impact of fragmentation on steppe plants. Steppe once covered vast, continuous areas, and nowadays is among the most fragmented biomes. In Ukraine, remnants of this habitat survived in large but few nature reserves and loess ravines as well as on kurgans (burial mounds of ancient nomadic people), which, despite their small size, are still numerous and scattered throughout the landscape.
We studied the impact of fragmentation on the genetic diversity and structure of Iris pumila, a typical species of European steppes. Our main focus was to compare the genetic characteristics between kurgan populations (n = 8), and populations from larger refugia (n = 6). We assessed the genetic diversity of the studied populations with Universal Rice Primers.
Our analyses revealed high genetic diversity across all investigated populations (mean He: 0.233; mean PPB: 58.57). However in kurgan populations genetic diversity was significantly higher than in larger refugia. Genetic diversity (He) was negatively correlated with population size. Most of the molecular variance (82%) was represented within populations, whereas genetic differentiation among populations was moderate (ΦST = 0.160), and low among refugia types (ΦRT = 0.026).
The maintenance of high genetic diversity despite two centuries of fragmentation may be related to the moderate disturbance occurring on kurgans, which enhances the sexual reproduction of the species. Moreover, we assume that species traits such as longevity and polyploidy might counterbalance genetic drift, while its self-incompatibility and presence of a soil seed bank allows for the replenishment of the gene pool. Overall, our results suggest that kurgans can protect genetic diversity of steppe species.
... The negative correlation between the climatic water deficit and germination probability could be due to reduced energy content of the seeds from dry populations, where mother plants likely faced drought stress during seed production (Hampton et al. 2013;Heinicke et al. 2016). However, in the dry treatment, total germination was positively affected by increasing climatic water deficit. ...
The recruitment life stage, including germination and early seedling establishment, is the most vulnerable life stage of plants and has cascading effects on plant performance at later life stages. However, surprisingly little is known on the eco-evolutionary processes that determine the success of biological invasions at this life stage.
We performed germination experiments with and without simulated drought stress and monitored early seedling growth in diploid and tetraploid Centaurea stoebe. While diploids are the major cytotype in the native European range, only tetraploids became invasive in North America. Thus, C. stoebe is an excellent model species to simultaneously study both, pre-adaptive differences in the native range (diploids vs. tetraploids) and post-introduction evolution in the non-native range (native tetraploids vs. non-native tetraploids). To account for broad spatial-environmental variation within cytotypes and ranges, we germinated 23,928 seeds from 208 widely distributed populations.
Tetraploids germinated better than diploids. Within tetraploids, invasive populations outperformed native populations in germination. However, these differences were not evident under simulated drought stress. Seedlings of invasive tetraploids had a higher biomass and developed the first true leaf earlier than those from the native range, while the native cytotypes did not differ in these early seedling traits.
Our results suggest that a combination of pre-adaptation related to superior performance of polyploids (greater and faster germination) and post-introduction evolution towards higher performance in the invasive range (greater and faster germination, greater and faster accumulation of seedling biomass) may have contributed to the invasion success of tetraploid C. stoebe in North America.
... (study area: Qinghai-Tibetan Plateau, SSR, He = 0.585; Liu et al., 2016). Compared with other Stipa species, such as Stipa pennata L. (study area: Kulunda steppe, ISSR, He = 0.132; Heinicke et al., 2016), Stipa grandis P.A.Smirn. (study area: Xilin River Basin, ISSR, He = 0.2522; Peng et al., 2015), S. krylovii (study area: Xilin River Basin, ISSR, He = 0.2261; Peng et al., 2015), and S. bungeana (study area: Loess Plateau, ISSR, He = 0.2066; Yu et al., 2014), S. breviflora represented a higher genetic diversity. ...
Historical and contemporary microevolutionary processes influence the extent and structure of genetic variation. Combining phylogeography and landscape genetics is an important approach for delineating the formation mechanisms about the patterns of genetic structures. Grassland ecosystems comprise approximately one-third of Earth’s vegetative cover. The spatial distribution of genetic variations derived from dominant plant species in steppes is helpful to understand the origin and evolution of this kind of vegetation. In this paper, we took Stipa breviflora, a dominant species of desert steppe, as an example, and conducted the research on both chloroplast DNA sequences and microsatellite loci of populations. The results of analyzing haplotype and microsatellite diversity revealed that S. breviflora most probably originated from the region in eastern Helan Mountains and northeast of Qinghai-Tibet Plateau (QTP) during the late Miocene. The genetic variation distribution of the species was in accordance with the core-periphery hypothesis (CPH), i.e., populations located at the periphery of a species’ range should have lower levels of genetic variation than those at the center of the range. Paleoclimatic fluctuations contributed to haplotype evolution, while geographical distance played an important role in driving contemporary genetic differentiation. Our findings highlight the complexity of intraspecific evolution and clarify the biogeographical history of desert steppes based on molecular signals.
... Genetic diversity may be the first of these to vanish when anthropogenic activities threaten plant populations (Spielman et al., 2004). Anthropogenic environmental changes such as habitat degradation and fragmentation decrease population sizes and limit gene flow among increasingly isolated populations (Young et al., 1996;Heinicke et al., 2016;González et al., 2020). Together, these processes may lead to genetic erosion, including an increase of genetic drift and biparental inbreeding, and the accumulation of deleterious mutations (Young et al., 1996;Hensen & Oberprieler, 2005;Hedrick & Garcia-Dorado, 2016). ...
Background and Aims
Habitat degradation and landscape fragmentation dramatically lower population sizes of rare plant species. Decreasing population sizes may, in turn, negatively affect genetic diversity and reproductive fitness which can ultimately lead to local extinction of populations. Although such extinction vortex dynamics have been postulated in theory and modelling for decades, empirical evidence from local extinctions of plant populations is scarce. In particular, comparisons between current vs. historical genetic diversity and differentiation are lacking despite their potential to guide conservation management.
Methods
We studied the population genetic signatures of the local extinction of Biscutella laevigata subsp. gracilis populations in Central Germany. We used microsatellites to genotype individuals from 15 current populations, one ex-situ population, and 81 herbarium samples from five extant and 22 extinct populations. In the current populations, we recorded population size and fitness proxies, collected seeds for a germination trial and conducted a vegetation survey. The latter served as surrogate for habitat conditions to study how habitat dissimilarity affects functional connectivity among the current populations.
Key Results
Bayesian clustering revealed similar gene pool distribution in current and historical samples but also indicated that a distinct genetic cluster was significantly associated with extinction probability. Gene flow was affected by both spatial distance and floristic composition of population sites, highlighting the potential of floristic composition as powerful predictor of functional connectivity which may promote decision making for reintroduction measures. For an extinct population, we found a negative relationship between sampling year and heterozygosity. Inbreeding negatively affected germination.
Conclusions
Our study illustrates the usefulness of historical DNA to study extinction vortices in threatened species. Our novel combination of classical population genetics together with data from herbarium specimens, an ex-situ population and a germination trial underscores the need for genetic rescue measures to prevent extinction of B. laevigata in Central Germany.
... Steppe ecosystems are among the most threatened in Europe due to the anthropogenic destruction and fragmentation of steppe patches (Cremene et al., 2005); however, publications that focus on the impact of habitat fragmentation on steppe vegetation are not numerous (Dembicz et al., 2018;Heinicke et al., 2016;Wódkiewicz et al., 2016). A recent review by Kajtoch et al. (2016) showed a low genetic variation in populations of plant species related to dry grasslands in Eastern Central Europe: 94% of the studied plant species (15 out of 16 taxa for which the data were available) had some or all of their populations characterized by low diversity, while highly diverse populations were found in 38% of taxa. ...
Habitat fragmentation is one of serious threats to biodiversity of nature in today's world. The present study of a typical steppe species Iris pumila L. (Iridaceae) has analyzed the impacts of geographical isolation and population size on genetic diversity and population structure in conditions of habitat fragmentation. The key indices of population genetic variability calculated from the ISSR markers data were on average as follows: Shannon diversity index (S)-0.188; unbiased Nei's gene diversity (H e)-0.123; and the average measure of Jaccard's genetic distances between individuals within populations-58.4%. Although the largest population had significantly higher values of S and He, the small and marginal populations also showed a comparable level of variation. Most of the genetic variation of I. pumila was distributed within the populations. A strong correlation was found between Nei's genetic distances and geographic distances between the populations. According to the Bayesian analysis, genetic structure of the populations was highly homogeneous; however, the presence of admixed genotypes indicated the possibility of gene flow between the populations at present.
... Yet, S. pennata, as a species distributed widely in Eurasian steppes (Kaźmierczakowa et al., 2014), is adapted to relatively dry climatic conditions prevailing there (Werger et al., 2012). Our results are consistent with previous research (Heinicke et al., 2016), which shows that southern Siberian S. pennata populations (in the case of size, density and genetic diversity), are negatively influenced by precipitation. ...
Increasing urbanisation has led to the fragmentation of natural habitats and biodiversity decline. In Central Europe, this fate has befallen semi-natural xerothermic grasslands. However, in the case of species well adapted to open habitats, urbanisation may positively affect dispersal. In many places specialised xerothermic species start to spread in secondary habitats such as roadsides or railway embankments. However, little is known about the genetic variability of such newly-established populations. In an era of growing anthropogenic pressure, understanding the role of secondary, anthropogenic habitats in the maintenance biodiversity should be considered a crucial issue in the conservation of species associated with Central European dry grasslands. Therefore, on the basis of a combined analysis of xerothermic species abundance, bioclimatic and soil data, and genetic diversity, we wish to examine the suitability of secondary habitats (as substitutes for primary) and to demonstrate their role in the conservation of xerothermic species. Our results suggest that smaller competition for light and greater habitat connectivity indicate suitability of habitats for xerothermic species conservation. On one hand, the occurrence of these species in secondary habitats may be limited by the pressure of expansive grasses, on the other, the negative impact of the latter is buffered by the reduced presence of shrubs, and thus the greater availability of light. Plant communities from secondary habitats are less richness in xerothermic species, and particular species are less abundant, for this reason secondary habitats should be treated more as refuges (with suboptimal conditions) than as substitution habitats. But yet, Stipa pennata populations from secondary habitats do not suffer from genetic depauperation. Populations from secondary habitats are characterised by comparable share of two genotypes, indicating existence of gene flow between populations from south and north-west part of studied area. Through the maintenance of meta-population processes by means of dynamic connectivity between habitats on a landscape scale, secondary habitats possess an undoubtedly high conservation value for xerothermic species.
https://authors.elsevier.com/a/1aGTI,XRNLctLo
... Population IDs and geographical information on the populations can be found in Table 1. speed, we recorded the ratio of germinated vs. non-germinated seeds at 1, 3, 5, 7, and 12 d after seeds were placed in Petri dishes, and calculated a modified Timson's Index (T I ) according to Heinicke et al. (2016) as follows: T I = (ΣG)/d (where G is the proportion of seeds of the seed family germinated at the census days and d is the number of census days). Timson's Index combines information about germination speed and total germination success (P erez-Fern andez et al. 2006). ...
Comparing genetic diversity, genetic differentiation, and performance between native and nonnative populations has advanced our knowledge of contemporary evolution and its ecological consequences. However, such between‐range comparisons can be complicated by high among‐population variation within native and nonnative ranges. For example, native vs. nonnative comparisons between small and non‐representative subsets of populations for species with very large distributions have the potential to mislead because they may not sufficiently account for within‐range adaptation to climatic conditions, and demographic history that may lead to non‐adaptive evolution. We used the cosmopolitan weed Conyza canadensis to study the interplay of adaptive and demographic processes across, to our knowledge, the broadest climatic gradient yet investigated in this context. To examine the distribution of genetic diversity, we genotyped 26 native and 26 nonnative populations at 12 microsatellite loci. Furthermore, we recorded performance traits for 12 native and 13 nonnative populations in the field and in the common garden. To analyze how performance was related to range and/or climate, we fit pedigree mixed‐effects models. These models weighed the population random effect for co‐ancestry to account for the influence of demographic history on phenotypic among‐population differentiation. Genetic diversity was very low, selfing rates were very high, and both were comparable between native and nonnative ranges. Nonnative populations out‐performed native populations in the field. However, our most salient result was that both neutral genetic differentiation and common garden performance were far more correlated with the climatic conditions from which populations originated than native vs. nonnative range affiliation. Including co‐ancestry of our populations in our models greatly increased explained variance and our ability to detect significant main effects for among‐population variation in performance. High propagule pressure and high selfing rates, in concert with the ability to adapt rapidly to climatic gradients, may have facilitated the global success of this weed. Neither native nor nonnative populations were homogeneous groups but responded comparably to similar environments in each range. We suggest that studies of contemporary evolution should consider widely distributed and genotyped populations to disentangle native vs. nonnative range effects from varying adaptive processes within ranges and from potentially confounding effects of demographic history.
... Combined studies on performance and genetic characterisation of steppe species are rare (and lacking for P. badensis) and concentrated mostly at a regional scale 1 3 (cf. Hensen et al. 2005;Dostálek et al. 2010;Lauterbach et al. 2011;Heinicke et al. 2016), with the exception of the work on Stipa capillata by Wagner et al. (2011a, b). ...
Many steppe species reach their (north)westernmost distribution limit in western Central Europe. This also applies to Poa badensis, a rare steppe plant of calcareous rock/sand vegetation. To explore potential differences in reproductive success and genetic composition of peripheral populations, we analysed the absolute (north)westernmost occurrences in Western Germany and populations at the western margin (Eastern Austria) and the centre (Central Hungary) of the Pannonicum, representing a part of the continuous range. Specifically, we discuss the genetic and reproductive constitution of the (north)westernmost exclave and draw conclusions on the species' biogeographical and conservation history in this region. Therefore, we used two independent molecular marker systems (AFLPs, cpDNA sequences) and a set of performance parameters. Overall, lowest regional genetic diversity was found in Western Germany, which is mainly a result of the specific history of two populations. However, this low genetic diversity was not accompanied by reduced reproductive success. The Eastern Austrian populations showed reduced genetic diversity and predominantly reduced performance, interpreted as a consequence of small population sizes. Central Hungarian populations showed the overall highest genetic diversity and comparatively high performance values. We observed high admixture and haplotype sharing between Austrian and Hungarian populations, indicating gene flow among these regions. In contrast, we interpreted the increased population differentiation within, and the clear distinctiveness of the German exclave as a long-term isolation of these (north)westernmost occurrences. Our results, overall, prove the good constitution of these populations and, together with their particular biogeographical history, highlight their conservation value.
... The observed effects of the maximum population size are thus unaffected by its correlation with the current management. Genetic diversity was also marginally significantly related to the isolation of the populations (e.g., Ellstrand and Elam 1993;Gonzalez-Astorga et al. 2004;Honnay et al. 2007;Heinicke et al. 2016), though the pattern is not ubiquitous (e.g., Young et al. 1999). ...
Assessing genetic diversity within populations of rare species and understanding its determinants are crucial for effective species protection. While a lot is known about the relationships between genetic diversity, fitness, and current population size, very few studies explored the effects of past population size. Knowledge of past population size may, however, improve our ability to predict future population fates. We studied Gentianella praecox subsp. bohemica, a biennial species with extensive seed bank. We tested the effect of current, past minimal and maximal population size, and harmonic mean of population sizes within the last 15 years on genetic diversity and fitness. Maximum population size over the last 15 years was the best predictor of expected heterozygosity of the populations and was significantly related to current population size and management. Plant fitness was significantly related to current as well as maximum population size and expected heterozygosity. The results suggested that information on past population size may improve our understanding of contemporary genetic diversity across populations. They demonstrated that despite the strong fluctuations in population size, large reductions in population size do not result in immediate loss of genetic diversity and reduction of fitness within the populations. This is likely due to the seed bank of the species serving as reservoir of the genetic diversity of the populations. From a conservation point of view, this suggests that the restoration of small populations of short-lived species with permanent seed bank is possible as these populations may still be genetically diverse.
... Consequently, many endangered species face genetic drift and increased levels of inbreeding (e.g. Heinicke et al. 2016). This is alarming, as a loss of genetic diversity is often accompanied by reduced reproductive fitness (reviewed in Leimu et al. 2006). ...
... Eckert, 2001). This is crucial for self-incompatible species where sexual reproduction becomes impaired or unreachable, but also bears fitness costs for self-compatible species (like many Stipa species) making them prone to stochastic loss of genetic diversity and subsequent extinction (Heinicke et al., 2016;comp. Loveless and Hamrick, 1984). ...
The habitat loss and fragmentation due to agricultural land-conversion affected the steppe throughout its range. In Ukraine, 95% of steppe was destroyed in the last two centuries. Remaining populations are confined to few refuges, like nature reserves, loess ravines, and kurgans (small burial mounds), the latter being often subject to destruction by archeological excavations.
Stipa capillata L. is a typical grass species of Eurasian steppes and extrazonal dry grasslands, that was previously used as a model species in studies on steppe ecology. The aim of our research was to assess genetic diversity of S. capillata populations within different types of steppe refuges (loess ravines, biosphere reserve, kurgan) and to evaluate the value of the latter group for the preservation of genetic diversity in the study species.
We assessed genetic diversity of 266 individuals from 15 populations (nine from kurgans, three from loess ravines and three from Askania-Nova Biosphere Reserve) with eight Universal Rice Primers (URPs).
Studied populations showed high intra-population variability (I: 0.262–0.419, PPB: 52.08–82.64%). Populations from kurgans showed higher genetic differentiation (ΦST = 0.247) than those from loess ravines (ΦST = 0.120) and the biosphere reserve (ΦST = 0.142). Although the diversity metrics were to a small extent lower for populations from kurgans than from larger refugia we conclude that all studied populations of the species still preserve high genetic variability and are valuable for protection. To what extent this pattern holds true under continuous fragmentation in the future must be carefully monitored.
Throughout Eurasia, steppes are preserved in forms of small fragmented areas within the landscapes of tilled fields, fallow lands, pastures, and infrastructural complexes. In Kulunda, steppes are preserved owing to the areas of alkaline steppe with saline soil complexes as well as secondary steppes formed in uncultivated lands. Intensive agriculture in the steppe and forest-steppe areas of Kulunda exerts the most significant impact such as total plowing of fertile lands, overgrazing by excessively numerous livestock, and inadequate agricultural technologies for certain agroclimatic and landscape-ecological conditions. This led to a whole range of consequences: destruction, fragmentation, and ecotonization of steppe communities, direct extermination of key plant species, forest and birch kolki clearance, biota unification and introduction of alien species, reduction of species and cenotic diversity in steppes as well as destruction of their structure and loss of self-regeneration and self-regulation ability. The start of human influence dates back to the Neolithic age (the cattle-raising stage of the territory development). However, the most devastating impact began in the twentieth century with the arable farming stage. Almost all tillable lands were plowed at the time of Stolypin’s agrarian reform in the beginning of the twentieth century and during the years of Khrushchev’s land reclamation campaign 1954–1955. Nowadays, agroecosystems have been formed in the places of former natural steppe ecosystems. The influence of agricultural reclamation on the vegetation cover and biodiversity distribution in the steppe and forest-steppe areas of Kulunda is to a large extent studied and documented.
The Eurasian steppes represent the continent’s share of the world’s temperate grasslands and once have formed one of the largest continuous terrestrial biomes at an extent of ca. 10 Mio km². The present chapter describes key aspects of steppes and puts the study region Kulunda in context giving overview data and maps on climate, flora and vegetation. Relatively dry conditions render tree growth limited throughout the biome, while grasses typically have high abundance. Major vegetation classes include meadow steppes often intersected with forest outposts (and then called forest steppe landscapes), typical steppes and dry steppes, all of which are present in the study region. Kulunda thus is a typical example of western Eurasian steppes, which receive a relatively large share of precipitation in winter. Spring conditions are not as dry as in neighbouring regions of Mongolia and China, resulting in a rich and partly specialised flora. Grasslands in the Kulunda region belong to the phytosociological class Festuco-Brometea, also highlighting similarities to western Eurasia rather than to the Mongolian plateau eastwards. The western Eurasian steppes have been subject to large-scale conversion to arable lands, and Kulunda is no exception. Less than 17% (ca. 28,000 km²) of the potential grassland cover still is extant. These sites contain a high number of locally threatened plant species and still reflect most of the former diversity of vegetation types found in this key Middle Asian steppe region.
Quaternary climatic oscillations are major determinants of biodiversity in Europe. Yet their consequences have rarely been assessed in species whose ranges were continuous in the cold spells but then became fragmented by expanding forest in the mid-Holocene into so-called interglacial refugia. The Galium pusillum group (Rubiaceae), occupying various island-like habitats from the lowlands to the subalpine belt of Central Europe, is well suited for addressing the processes shaping genetic and cytological diversity of island populations and testing whether they leave distinct footprints in different habitat types. Using amplified fragment length polymorphism (AFLP) analysis and plastid sequences, we estimated the diversity and differentiation of 15 diploid and 44 tetraploid populations. Although the frequency of ploidy levels differed between low- and high-elevation stands, genetic diversity was homogeneous across various habitat types and elevations. Overall, high diversity probably reflects long-term local persistence of the group that was followed by fragmentation into isolated but probably stable populations that do not show signs of diversity loss. Moreover, hybridization pre-dating the contemporary fragmentation further increased overall diversity and was probably involved in the formation of a local subalpine endemic. In sum, our study shows that low-competition habitats of various substrates and elevations may play comparable roles in preserving distinct plant diversity.
An investigation in the southern part of the “virgin land zone” in Central Kazakstan, fallow fields and the natural short grass steppe was carried out. Surveys on soil and vegetation was made. Also, the change of land use due to the recent financial crisis and transformation processes in the Republic of Kazakstan were observed. The investigations was carried out, on four former state farms (sovkhozes) east of Lake Tengiz. We compared vegetation on fallow fields and “seed grassland” at different stages of succession. We found that on fallows and “seed grassland”, up to 20 years after the soil was last tilled, the number of returning steppe plants increased. Full succession back to a natural, short grass steppe lasts longer. Thus, a full regeneration in this time span is not possible. The vegetation cover of fallows shows a typical patchy pattern due to different dominant plant species. On the contrary, the short grass steppe does not show this.
Light and middle chestnut-colored soil of steppes and fallows were compared. One result was a significant loss of organic matter (humus) in the top layer, which might be due to wind erosion and a lack of fertilizer. We observed salt accumulation on fallows only locally. The former sovkhozes were founded 40 years ago to grow weed. The precipitation is so low that, even in Soviet times, the sovhhozes received subsidies from Moscow. The lack of subsidies, and the general crisis striking the area have resulted in a massive migration towards the bigger cities. Less than half of the fields are still in use for crop farming, thus the number of fallow fields have reached historic proportions.
The investigations contribute basic knowledge for the development and management of the future biosphere reserve of UNESCO (Program: man and biosphere) at lake Tengiz. The Ernst-MoritzArndt University helps the Kazakh government to implement and develop the reserve.
Ecological restoration of grasslands is increasingly based on regional seeds derived from predefined seed transfer zones. However, the degree and spatial pattern of genetic differentiation among provenances of different seed transfer zones is largely unknown.
We assessed the genetic differentiation among eight out of 22 German seed transfer zones for seven common grassland species ( Arrhenatherum elatius, Centaurea jacea, Daucus carota, Galium album, Hypochaeris radicata, Knautia arvensis and Lychnis flos‐cuculi ) using AFLP markers. We analysed genetic population structure with AMOVA and Bayesian cluster analysis and tested for isolation by distance and isolation by environment.
In all of the investigated species, almost all pairs of provenances were genetically differentiated. Bayesian cluster analysis revealed species‐specific numbers and spatial patterns of gene pools, with between two ( Arrhenatherum ) and eight clusters ( Lychnis ). Most investigated seed transfer zones represented a unique gene pool in the majority of the species.
We found isolation by distance in four species, isolation by environment, driven by climatic seasonality, in three species, and a lack of both in three species. Thus, the observed genetic differentiation appears to be caused by both neutral and adaptive processes.
Synthesis and applications . Our study shows that grassland plants are indeed strongly genetically differentiated across Germany supporting the strategy of seed transfer zones for ecological restoration. Although the predefined seed transfer zones are unlikely to match the exact genetic structure of many species, they serve their purpose by capturing a substantial amount of intraspecific genetic variation across species.
A common assumption in ecology and evolutionary biology is that genetic diversity declines and differentiation increases toward the edge of a species’ geographic range, where populations tend to be smaller and more isolated. We tested these predictions in a characteristic Eurasian steppe plant, Stipa pennata, by inspecting 230 AFLP bands in 26 populations (345 individuals) along a 3300-km longitudinal gradient from the range core, in Russia, to the range periphery, in central Europe. Overall, our study species showed low genetic diversity within populations (mean proportion of polymorphic ) and moderately high genetic differentiation among them (mean ). As predicted, genetic diversity declined significantly from the range core to the periphery but was not correlated with population size. Pairwise genetic differentiation was significantly higher among peripheral populations than central populations but did not show a pronounced relationship with geographic distance. Our results indicate that peripheral populations may experience higher genetic drift and lower gene flow than their central counterparts, possibly because of smaller population sizes, spatial isolation, and a more complex landscape structure. In addition, historic range fluctuations and the mixed breeding system could have enhanced the observed patterns in our study species.
Wild populations face threats both from deterministic factors, e.g., habitat loss, overexploitation, pollution, and introduced species, and from stochastic events of a demographic, genetic, and environmental nature, including catastrophes. Inbreeding reduces reproductive fitness in naturally outbreeding species, but its role in extinctions of wild populations is controversial. To evaluate critically the role of inbreeding in extinction, we conducted realistic population viability analyses of 20 threatened species, with and without inbreeding depression, using initial population sizes of 50, 250, and 1000. Inbreeding markedly decreased median times to extinction by 28.5, 30.5, and 25% for initial populations of 50, 250, and 1000, respectively, and the impacts were similar across major taxa. The major variable explaining differences among species was initial population growth rate, whereas the impact of inbreeding was least in species with negative growth rates. These results demonstrate that the prospects for survival of threatened species will usually be seriously overestimated if genetic factors are disregarded, and that inappropriate recovery plans may be instituted if inbreeding depression is ignored. Copyright © 2002 by the author(s). Published here under licence by The Resilience Alliance.
A highly selfing breeding system affects gene flow, which may have consequences for patterns of genetic variation and differentiation on both the population and species level. Feather grasses (Stipa spp.) are dominant elements of Eurasian steppes that persist in Central Europe in scattered isolated populations that are of great conservation interest. Cleistogamy is common in the Stipa pennata group, the phylogeny of which is largely unresolved. Intraspecific patterns of genetic variation can be characterised by lack of gene flow due to selfing, but also by large-scale historical migrations and long-term isolation. We analysed both 5 species within the S. pennata group and 33 populations of Stipa pulcherrima sampled across a large part of its range. Using AFLP markers we assessed phylogenetic relationships of the S. pennata group and patterns of genetic variation within and among populations. The S. pennata group formed a consistent clade separated from S. capillata. Stipa pulcherrima was sister to S. eriocaulis, but the relationships among S. pennata s. str., S. borysthenica., and S. tirsa remained unresolved. Within-population genetic variation was extremely low in all species of the S. pennata group (H
e = 0.0–0.013). In S. pulcherrima, genetic variation was consistently relatively high in the east (Romania, Russia) and declined toward western populations, with many populations at the western range edge lacking genetic variation entirely. Populations were strongly differentiated (F
ST = 0.762), and this differentiation did not follow a classical pattern of isolation by distance. Bayesian cluster analysis revealed nine gene pools in S. pulcherrima, which were mostly geographically clustered. Overall the results suggest that S. pulcherrima and species of the S. pennata group are characterised by a cleistogamous breeding system leading to extremely low levels of genetic variation and high levels of population differentiation at both the population and species level. Postglacial colonisation, current population isolation, and population bottlenecks at the western range periphery have further reduced genetic variation and obviated gene exchange. Thus, genetic variation can only be preserved by the conservation of multiple populations.
AFLP markers are often used to study patterns of population genetic variation and gene flow because they offer a good coverage of the nuclear genome, but the reliability of AFLP scoring is critical. To assess interspecific gene flow in two African rainforest liana species (Haumania danckelmaniana, H. liebrechtsiana) where previous evidence of chloroplast captures questioned the importance of hybridization and species boundaries, we developed new AFLP markers and a novel approach to select reliable bands from their degree of reproducibility. The latter is based on the estimation of the broad-sense heritability of AFLP phenotypes, an improvement over classical scoring error rates, which showed that the polymorphism of most AFLP bands was affected by a substantial nongenetic component. Therefore, using a quantitative genetics framework, we also modified an existing estimator of pairwise kinship coefficient between individuals correcting for the limited heritability of markers. Bayesian clustering confirms the recognition of the two Haumania species. Nevertheless, the decay of the relatedness between individuals of distinct species with geographic distance demonstrates that hybridization affects the nuclear genome. In conclusion, although we showed that AFLP markers might be substantially affected by nongenetic factors, their analysis using the new methods developed considerably advanced our understanding of the pattern of gene flow in our model species.
Although the potential genetic risks associated with rare or endangered plants and small populations have been discussed previously, the practical role of population genetics in plant conservation remains unclear. Using theory and the available data, we examine the effects of genetic drift, inbreeding, and gene flow on genetic diversity and fitness in rare plants and small populations. We identify those circumstances that are likely to put these plant species and populations at genetic risk. Warning signs that populations may be vulnerable include changes in factors such as population size, degree of isolation, and fitness. When possible, we suggest potential management strategies.
The proposal is made that seed scientists need an internationally acceptable hierarchical system of classification for seed dormancy. Further, we suggest that a modified version of the scheme of the Russian seed physiologist Marianna G. Nikolaeva be adopted. The modified system includes three hierarchical layers – class, level and type; thus, a class may contain levels and types, and a level may contain only types. The system includes five classes of dormancy: physiological dormancy (PD), morphological dormancy (MD), morphophysiological dormancy (MPD), physical dormancy (PY) and combinational dormancy (PY + PD). The most extensive classification schemes are for PD, which contains three levels and five types (in the non-deep level), and MPD, which contains eight levels but no types. PY is not subdivided at all but probably should be, for reasons given. Justifications are presented for not including mechanical dormancy or chemical dormancy in the modified scheme. PD (non-deep level) is the most common kind of dormancy, and occurs in gymnosperms (Coniferales, Gnetales) and in all major clades of angiosperms. Since, first, this is the class and level of dormancy in seeds of wild populations of Arabidopsis thaliana and, secondly, Type 1 (to which seeds of A. thaliana belong) is also common, and geographically and phylogenetically widespread, it seems that biochemical, molecular and genetic studies on seed dormancy in this model species might have rather broad application in explaining the basic mechanism(s) of physiological dormancy in seeds.
Human impacts on the natural environment have reached such proportions that in addition to an ‘extinction crisis’, we now also face a broader ‘biome crisis’. Here we identify the world's terrestrial biomes and, at a finer spatial scale, ecoregions in which biodiversity and ecological function are at greatest risk because of extensive habitat conversion and limited habitat protection. Habitat conversion exceeds habitat protection by a ratio of 8 : 1 in temperate grasslands and Mediterranean biomes, and 10 : 1 in more than 140 ecoregions. These regions include some of the most biologically distinctive, species rich ecosystems on Earth, as well as the last home of many threatened and endangered species. Confronting the biome crisis requires a concerted and comprehensive response aimed at protecting not only species, but the variety of landscapes, ecological interactions, and evolutionary pressures that sustain biodiversity, generate ecosystem services, and evolve new species in the future.
In the present paper we studied the life history traits related to seed germination of Stipa tenacissima, a key species in semiarid environments of western Mediterranean areas. S. tenacissima is a perennial tussock grass, which has traditionally been considered to expand mainly by vegetative propagation with little or no sexual reproduction. We analysed seed longevity as well as the type of seed dormancy and the role of the seed covers from seeds collected from different populations in SE Spain. We also studied the variation in seed germinability among populations, individuals, and years and the ability of seeds of S. tenacissima to form soil seed banks. There was significant variation in seed germination among individuals, populations and years. Lemma and palea were the main factor controlling these differences since their removal promoted higher and faster germination and eliminated the differences in germination parameters among populations. However, the control of dormancy by lemma and palea was independent of their weight, suggesting that their chemical nature plays a more important role than does size in controlling seed germination. Mechanical scarification treatments (via abrasion with sand) did not affect seed germination. The decay in seed germinability two years after seed collection and the low density of viable seeds in soils one year after seed dispersal indicated that S. tenacissima forms transient soil seed banks.
Changes in agricultural production methods over the last century have caused a massive reduction and fragmentation of the area of European semi-natural grasslands. It remains unclear whether small and isolated grassland fragments can support viable plant populations in a sustainable way. In our study area in southern Belgium, the extent of calcareous grasslands was reduced from c. 650 ha in 1775 to less than 30 ha in 2004. We used AFLP markers to quantify the effects of present and historical grassland fragmentation on the genetic structure of 27 populations of the rare perennial plant species Globularia bisnagarica. Given the mixed breeding system of the species and the relatively small area of the studied system, the populations were characterized by high genetic differentiation (F
st range: 0.42–0.48; Φst=0.53). A Mantel test revealed significant isolation by distance of the populations. Average within population genetic diversity, measured as expected heterozygosity or gene diversity, was low (H
j
=0.081) and was negatively related to population isolation. This suggests more gene flow into less isolated populations. Population size and local habitat characteristics did not significantly influence population genetic diversity. Both, high selfing rates in G. bisnagarica and a population genetic response to habitat fragmentation may explain our findings. Finally, a clear geographical clustering was observed, with cluster membership partially explainable by historical grassland connectivity. If populations indeed started to differentiate after fragmentation, this process was not (yet) strong enough to erase the genetic similarity between fragments that historically belonged to the same large grassland fragment.
Stipa-species are wide-spread in Central Asia, but sexual reproduction in the dry steppes is rare. To facilitate conservation and
restoration of these important rangelands, we studied germination characteristics of three common Mongolian Stipa-species under field- and lab conditions. Seeds of Stipa krylovii, Stipa gobica and Stipa glareosa were sown at the study site in Southern Mongolia over two consecutive years during which period tests were carried out to
ascertain whether competition or herbivory are the main constraints of seedling establishment. In addition, we tested germination
and seed viability in the laboratory under two different temperature regimes (20/10°C and 8/4°C), as well as the effect of
cold-stratification. The lab experiments also included S.krylovii seeds originating from three climatically different provenances. None of the three Stipa-species seedlings emerged during the first 2years of the field study. However, after an unusually intense rain event in
the third year, 3% of S.krylovii, 0.6% of S.glareosa and 0.1% of S.gobica seeds germinated in the study plots. The factors ‘sowing-year’ and ‘vegetation’ significantly affected seedling emergence,
whereas grazing had no effect at all. Under laboratory conditions a high percentage of viable seeds of S.gobica and S.glareosa germinated at both incubation temperatures, and cold-stratification had no effect on germination or viability. Germination
of S.krylovii seeds required warmer temperatures and cold-stratification had a positive effect. Such evidence for dormancy was more pronounced
in seeds from the moister, northern provenances. Germination of Stipa-species in the field is rare and only possible under exceptionally moist conditions. Conservation should thus concentrate
on steppe conservation rather than on restoration. Where artificial reseeding is necessary, differences among species and
also among different seed provenances should be taken into account.
We developed interpolated climate surfaces for global land areas (excluding Antarctica) at a spatial resolution of 30 arc s (often referred to as 1-km spatial resolution). The climate elements considered were monthly precipitation and mean, minimum, and maximum temperature. Input data were gathered from a variety of sources and, where possible, were restricted to records from the 1950-2000 period. We used the thin-plate smoothing spline algorithm implemented in the ANUSPLIN package for interpolation, using latitude, longitude, and elevation as independent variables. We quantified uncertainty arising from the input data and the interpolation by mapping weather station density, elevation bias in the weather stations, and elevation variation within grid cells and through data partitioning and cross validation. Elevation bias tended to be negative (stations lower than expected) at high latitudes but positive in the tropics. Uncertainty is highest in mountainous and in poorly sampled areas. Data partitioning showed high uncertainty of the surfaces on isolated islands, e.g. in the Pacific. Aggregating the elevation and climate data to 10 arc min resolution showed an enormous variation within grid cells, illustrating the value of high-resolution surfaces. A comparison with an existing data set at 10 arc min resolution showed overall agreement, but with significant variation in some regions. A comparison with two high-resolution data sets for the United States also identified areas with large local differences, particularly in mountainous areas. Compared to previous global climatologies, ours has the following advantages: the data are at a higher spatial resolution (400 times greater or more); more weather station records were used; improved elevation data were used; and more information about spatial patterns of uncertainty in the data is available. Owing to the overall low density of available climate stations, our surfaces do not capture of all variation that may occur at a resolution of 1 km, particularly of precipitation in mountainous areas. In future work, such variation might be captured through knowledge-based methods and inclusion of additional co-variates, particularly layers obtained through remote sensing.
Abstract spagedi version 1.0 is a software primarily designed to characterize the spatial genetic structure of mapped individuals or populations using genotype data of codominant markers. It computes various statistics describing genetic relatedness or differentiation between individuals or populations by pairwise comparisons and tests their significance by appropriate numerical resampling. spagedi is useful for: (i) detecting isolation by distance within or among populations and estimating gene dispersal parameters; (ii) assessing genetic relatedness between individuals and its actual variance, a parameter of interest for marker based inferences of quantitative inheritance; (iii) assessing genetic differentiation among populations, including the case of haploids or autopolyploids.
This is the second edition of a multi-author book first published in 1992. It deals with all aspects of plant regeneration by seeds, including reproductive allocation, seed dispersal and predation, longevity, dormancy and germination. All chapters have been updated, and four new chapters added on seed size, seedling establishment, the role of gaps, and regeneration from seed after fire.
A guide to using S environments to perform statistical analyses providing both an introduction to the use of S and a course in modern statistical methods. The emphasis is on presenting practical problems and full analyses of real data sets.
The new edition of Seeds contains new information on many topics discussed in the first edition, such as fruit/seed heteromorphism, breaking of physical dormancy and effects of inbreeding depression on germination. New topics have been added to each chapter, including dichotomous keys to types of seeds and kinds of dormancy; a hierarchical dormancy classification system; role of seed banks in restoration of plant communities; and seed germination in relation to parental effects, pollen competition, local adaption, climate change and karrikinolide in smoke from burning plants. The database for the world biogeography of seed dormancy has been expanded from 3,580 to about 13,600 species. New insights are presented on seed dormancy and germination ecology of species with specialized life cycles or habitat requirements such as orchids, parasitic, aquatics and halophytes. Information from various fields of science has been combined with seed dormancy data to increase our understanding of the evolutionary/phylogenetic origins and relationships of the various kinds of seed dormancy (and nondormancy) and the conditions under which each may have evolved. This comprehensive synthesis of information on the ecology, biogeography and evolution of seeds provides a thorough overview of whole-seed biology that will facilitate and help focus research efforts.
What determines the number and size of the seeds produced by a plant? How often should it reproduce them? How often should a plant produce them? Why and how are seeds dispersed, and what are the implications for the diversity and composition of vegetation? These are just some of the questions tackled in this wide-ranging review of the role of seeds in the ecology of plants. The authors bring together information on the ecological aspects of seed biology, starting with a consideration of reproductive strategies in seed plants and progressing through the life cycle, covering seed maturation, dispersal, storage in the soil, dormancy, germination, seedling establishment, and regeneration in the field. The text encompasses a wide range of concepts of general relevance to plant ecology, reflecting the central role that the study of seed ecology has played in elucidating many fundamental aspects of plant community function.
The chapter introduces the idea that the relationships between natural conditions and the outcome of an observation may be deterministic, random, strategic or chaotic, and that numerical ecology addresses the second type of data; it describes the role of numerical ecology among the various phases of an ecological research. The chapter includes discussion of the following topics: spatial structure, spatial dependence, and spatial correlation (independent observations, independent descriptors, linear independence, independent variable of a model, independent samples, origin of spatial structures, tests of significance in the presence of spatial correlation, and classical sampling and spatial structure), statistical testing by permutation (classical tests of significance, permutation tests, alternative types of permutation tests), computer programs and packages, ecological descriptors (i.e. variables: mathematical types of descriptors, and intensive, extensive, additive, and non-additive descriptors), descriptor coding (linear transformation, nonlinear transformations, combining descriptors, ranging and standardization, implicit transformation in association coefficients, normalization, dummy variable coding, and treatment of missing data (delete rows or columns, accommodate algorithms to missing data, estimate missing values). The chapter ends on a description of relevant software implemented in the R language.
AbSh8Ct Tes8s wintergur (St&a k&cot&ha Trin. & Rupr.) is 8n impor-tint cool-serron, perennl8l for8ge gr8ss in Tcur. Seed kndling problems urd 8 limited knowledge of germination 8nd est8blish-ment requirements have severely lhnited its use in reveget8tioa progmms. This study ~8s designed to chrrclcterize floret morphoi-ogy urd investigate the effects of different temperature X w8ter potenti8l regimes on germin8tion responses of ch8smog8mous 8nd b8s8l8xill8ry cieistog8mous florets from 2 Tests rrintergriss pop-ul8tions in central Text. Germination responses were evrluated 8t polyethylene glycol-inducsd w8ter potenti8ls of 0, -0.25, -0.50, -0.75, 8nd -1.0 MP8 under 8ltenuting temper8ture regimes of 10/20,15/25, and 201300 C in controlled environment ch8mbers. Awns contributed most to the weight of ch8smog8mous florets, while cuyopsss contributed most to the weight of cleistog8mous florets. Cieistog8mous florets generally hrd higher cumulrtive germhutioo percent8gee 8nd slower germh18tioo nta th8n ch8s-mog8mous florets in the vuious temperature X water potentkl reghnes. Cumul8tive germhutioo percentrgen of both floret types were greatest 8t substrate w8ter poteoti8ls of 0 8nd -0.25 MPa in the lo/200 C temper&we reghne, 8nd me8n germhution times were most npid 8t the 0 MPa subante water potenti in the lS/250 C temperature regime. Bued upon se8son8l temperrture md moisture conditions in centrrl Teur, germhmtion from n8tu-r8l seed b8nks or 8rtifici81 seedings should occur prhn8rily between l8te September urd mid-November, 8nd occasion8lly from De-cemba through Febru8ry during mild winters.
In drylands, primary production is predominantly limited by water availability; however, there is evidence for co-limitation by nutrients. We tested whether improved water and nutrient availability facilitate reproduction of dominant steppe species, and studied the effects of increased moisture and fertilization on seed production of the steppe grass Stipa krylovii.Effects of water availability on seed production and seed viability were investigated in a large-scale study on three sites with decreasing precipitation in Mongolia, over three to five consecutive years. In dry southern Mongolia, we additionally conducted an in situ irrigation and fertilization experiment to clarify the role of environmentally induced effects on seed production.Seed viability of S. krylovii was negatively correlated with annual precipitation over five years at the driest study site. The relation between annual precipitation and seed viability in the large-scale study was not as clear, however, in the two moister regions there was a trend of lower seed viability. Experimental irrigation also significantly decreased seed viability and seed mass. Seed production per hectare was not affected by irrigation, while fertilization resulted in a more than fivefold increase in both seed weight and number of viable seeds. The underlying mechanisms for these unexpected results were not investigated. However, a switch from cleistogamous pollination under dry conditions to less effective cross-pollination in moist years may be an explanation. Our data indicate that plant reproduction may show complex and unexpected reactions, and that nutrient limitation must be considered in global change scenarios even for dry regions.
Fragmentation and isolation of plant populations are thought to affect demographic processes such as seed production and cause reductions in fitness. I followed seed set over a 3-year period in eight populations of the endangered Rutidosis leptorrhynchoides (Asteraceae) that differed in population size from 13 to over 5000 flowering plants. Germinability of the resultant seed was also examined to determine whether small populations had lower fitness than large populations. Seed set was significantly associated with population size in 2 of the 3 years. Small populations (<30 flowering plants) produced significantly fewer seeds per head in 1994 and 1995 than did large populations (500 to over 5000 flowering plants), which did not differ significantly from one another. There was, however, substantial variation within populations. In 1993 seed production did not follow any simple relationship with population size, possibly because environmental stress from low rainfall had an overriding impact. Differences in seed germinability between populations were largely not evident, suggesting that this aspect of fitness has not declined substantially in small populations relative to large populations. This study suggests that nongenetic, demographic factors are of immediate importance to the persistence of small populations of R. leptorrhynchoides because of their potential impacts on seedling recruitment.
Lathyrus vernus (L.) Bernh. is a diploid, long-lived perennial and insect-pollinated herb with no special adaptation to long-distance dispersal. It occurs on neutral soil in deciduous forests throughout western Eurasia. Due to specific habitat preferences,L. vernus has a fragmented distribution with isolated populations. We investigated allozyme variation at eleven loci in 20 populations ofL. vernus from one geographically central region (the Czech Republic and the Slovak Republic) and two geographically marginal regions (southern and central Sweden) in the species present-day distribution. There was a clear differentiation between the three regions and the genetic distance between the populations was highly correlated with geographic distance. The total genetic diversity (HT) was 0.354. The proportion of genetic diversity due to differentiation between regions, and to differentiation between populations within regions, accounted for 10% each. There was no difference in level of genetic diversity between the three regions. No significant difference in level of genetic diversity was found between small and large populations. The genetic diversity inL. vernus may either be a result of the long generation-time of the species or peculiarities in the post-glacial migration species, e.g. survival only in refugia far east of the sampled populations and/or migration as a continuous process not involving founder-events.
Strong environmental gradients can affect the genetic structure of plant populations, but little is known as to whether closely related species respond similarly or idiosyn-cratically to ecogeographic variation. We analysed the extent to which gradients in temperature and rainfall shape the genetic structure of four Stipa species in four bio-climatic regions in Jordan. Genetic diversity, differentiation and structure of Stipa species were investigated using amplified fragment length polymorphism (AFLP) molecular markers. For each of the four study species, we sampled 120 individuals from ten populations situated in distinct bioclimatic regions and assessed the degree of genetic diversity and genetic differentiation within and among populations. The widespread ruderals Stipa capensis and S. parviflora had higher genetic diversity than the geographically restricted semi-desert species S. arabica and S. lagascae. In three of the four species, genetic diversity strongly decreased with precipitation, while genetic diversity increased with temperature in S. capensis. Most genetic diversity resided among populations in the semi-desert species (Φ ST = 0.572/0.595 in S. arab-ica/lagascae) but within populations in the ruderal species (Φ ST = 0.355/0.387 S. cap-ensis/parviflora). Principal coordinate analysis (PCoA) and STRUCTURE analysis showed that Stipa populations of all species clustered ecogeographically. A genome scan revealed that divergent selection at particular AFLP loci contributed to genetic differentiation. Irrespective of their different life histories, Stipa species responded similarly to the bioclimatic gradient in Jordan. We conclude that, in addition to predominant random processes, steep climatic gradients might shape the genetic structure of plant populations.
Aim To assess the effects of altitude and historic and recent forest fragmentation on the genetic diversity and structure of the wind-pollinated tropical tree line species Polylepis incana.
Location One of the highest mountain forest regions of the world, located in the Eastern Cordillera of the Ecuadorian Andes.
Methods We compared genetic diversity and structure of adult trees with those of seedlings (n= 118 in both cases) in nine forest stands spanning an altitudinal gradient from 3500 to 4100 m a.s.l. using amplified fragment length polymorphisms (AFLPs). Genetic diversity was calculated as percentage of polymorphic bands (P) and Nei's expected heterozygosity (He); genetic differentiation was assessed using analysis of molecular variance, ΦST statistics and Bayesian cluster analysis.
Results Estimates of genetic diversity at the population level were significantly lower in seedlings than in adults. Genetic diversity (He-value) was, in both cases, negatively correlated to altitude and positively correlated to population size in the seedlings. Genetic differentiation of the seedlings was approximately as high (φST= 0.298) as that of the adults (φST= 0.307), and geographical differentiation was clearly reflected in both AFLP profiles, with mountain ridges acting as barriers to gene flow.
Main conclusions Our study provides evidence of a historic upslope migration of P. incana in central Ecuador. In addition, it highlights the detrimental effects of unexpectedly strong genetic isolation, both recent and historical, particularly for our wind-pollinated species where the distance between forest stands was less than 25 km. We therefore additionally propose that in habitats with pronounced high-mountain landscape structures, gene flow may be hampered to such an extent that species have a more pronounced sensitivity to habitat fragmentation, even among populations of wind-pollinated trees.
Genetic variation in seven relict populations of Saxifraga cernua from three regions of the Alps was investigated using RAPD (random amplified polymorphic DNA) markers. No variation, either within the populations or within the regions, could be demonstrated. Nevertheless, each alpine region was characterized by a unique RAPD phenotype. Absence of genetic variation in these relict populations is attributed to population bottlenecks and founder effects during or following the ice ages. Contrasting hypotheses about the history of these populations, either as survivors of the glacial period or as products of postglacial immigration, are discussed in the light of the data presented.
Relationships between plant population size, fitness and within‐population genetic diversity are fundamental for plant ecology, evolution and conservation. We conducted meta‐analyses of studies published between 1987 and 2005 to test whether these relationships are generally positive, whether they are sensitive to methodological differences among studies, whether they differ between species of different life span, mating system or rarity and whether they depend on the size ranges of the studied populations.
Mean correlations between population size, fitness and genetic variation were all significantly positive. The positive correlation between population size and female fitness tended to be stronger in field studies than in common garden studies, and the positive correlation between genetic variation and fitness was significantly stronger in DNA than in isoenzyme studies.
The strength and direction of correlations between population size, fitness and genetic variation were independent of plant life span and the size range of the studied populations. The mean correlations tended to be stronger for the rare species than for common species.
Expected heterozygosity, the number of alleles and the number or proportion of polymorphic loci significantly increased with population size, but the level of inbreeding F IS was independent of population size. The positive relationship between population size and the number of alleles and the number or proportion of polymorphic loci was stronger in self‐incompatible than in self‐compatible species. Furthermore, fitness and genetic variation were positively correlated in self‐incompatible species, but independent of each other in self‐compatible species.
The close relationships between population size, genetic variation and fitness suggest that population size should always be taken into account in multipopulation studies of plant fitness or genetic variation.
The observed generality of the positive relationships between population size, plant fitness and genetic diversity implies that the negative effects of habitat fragmentation on plant fitness and genetic variation are common. Moreover, the stronger positive associations observed in self‐incompatible species and to some degree in rare species, suggest that these species are most prone to the negative effects of habitat fragmentation.
During the next century, natural and agricultural systems might need to adjust to a rapid increase in atmospheric CO2 concentration and global temperature. Evolution of genotypes adapted to this global change could play a central role in plants' response. The main purpose of this study was to determine the relative importance of phenotypic and genotypic responses of plants to global change. To do so, we selected two populations of the short-lived Brassica juncea, one under ambient conditions and another one under conditions simulating global change. After seven generations of selection, differences between the two populations were examined using a reciprocal transplant garden. We monitored 14 different traits and found evidence for genetic adaptation only once, for vegetative biomass early in the growth cycle. Of the 14 traits, 11 responded plastically to the environment, but only one of these plastic changes had a possible adaptive value. Overall, the long-term evolutionary consequences of global change will depend on the response of fitness-related traits. None of the five reproductive traits measured showed any evolutionary responses. The main conclusion of our study is that Brassica juncea was apparently unable to respond evolutionarily to simulated global change either by genetic adaptation or by adaptive phenotypic plasticity. The limit to selection was apparently due to inbreeding depression induced by the harsh conditions of the predicted environment.
It is widely assumed that population size significantly affects the dynamics of plant populations. Smaller populations are threatened by genetic drift and inbreeding depression, both of which may result in a decrease of genetic variation and a resulting negative impact on plant fitness. In our study we analysed the patterns of random amplified polymorphic DNA (RAPD) variation among 10 Dictamnus albuspopulations of varying size. The aim was to examine local differentiation in relation to spatial isolation resulting from limited population size and geographical distancing between populations. Significant correlations were noted between population size and both percentage of polymorphic loci (P < 0.01) and genetic diversity (P < 0.01). The matrix correlation between genetic and geographical distances revealed that geographical differentiation was reflected in the RAPD profile (Mantel test: r
2=0.34, P < 0.001). We found the highest level of molecular variance of RAPD patterns among individuals within the populations (72.6%), whereas among-population variation accounted for only 21.6% of variation. These results were highly significant in that they indicated a restricted population differentiation, as would be expected from outcrossing species. An additional analysis of seed production showed that there was significant variation among populations in terms of mean seed number per flower and mean seed mass per population which could be attributed to differences in population size as well as levels of genetic variation.
Biogeographic comparisons help to identify similarities, differences, larger contexts, and useful hypotheses. Between the (extra-tropical) Northern and Southern Hemispheres taxonomy differs almost completely, but other useful bases for vegetation comparison include phenophysiognomy, form composition and vegetation architecture, subphysiognomic morphology, environmental limits of plant types, taxonomic richness, and some aspects of function. All major biome types occur in both hemispheres except the boreal forests and analogous montane coniferous forests of the Northern Hemisphere. Some vegetation and plant types appear clearly unique, including Eucalyptus, campo cerrado, and flat-cushions such as Azorella, all of these in the Southern Hemisphere. Different but parallel adaptations to different but analogous conditions include the tall submediterranean forests, temperate rainforests, and continental versus maritime temperate deserts. Climatic limits appear similar in the two hemispheres, but mechanisms for some differences remain unresolved. Per unit land area, the Southern Hemisphere has higher annual net primary productivity than the Northern. Dissimilar analogs continue to suggest hypotheses and research questions.
Genetic variability in RAPDs (Randomly Amplified Polymorphic DNA) was studied in 104 genotypes of wild barley, Hordeum spontaneum from 21 populations sampled in Israel, Turkey and Iran, seven population from each country. The band (= loci) frequencies were calculated for each population and correlated with ecogeographical variables. In general, high RAPD genetic diversity indices were associated with stressful environments, either with hot or cold steppes and deserts. Interpopulational genetic distances showed no association with the geographic distance between the populations' provenance. Significant Spearman rank correlations between RAPD band frequencies and ecogeographical parameters of provenance occured. Frequencies of RAPD bands were significantly correlated with the principal component factors of allozymes. The correlation data indirectly suggest that natural selection appears to be the major determinant of both RAPD and allozyme diversities both being correlated with environmental stress.
AFLP markers were evaluated for their usefulness in the genetic analysis of sugarbeet and wild Beta species. Accessions of ten different sugarbeet breeding lines and five wild beets were screened using 256 primer combinations.
Of the 11 309 bands investigated, 96.4% were polymorphic among the accessions. A strong positive correlation was found between
the number of polymorphisms and AT content of the selective bases of the primer combinations. Random subsets of primer combinations
were used to produce genetic distance trees. Permutation tests showed that, for the wild beets, 500 AFLP bands sufficed to
obtain the best topology of the tree with a probability at any given node of more than 99%. Ten times as many bands were necessary
to obtain support values of the same order of magnitude for the sugarbeet lines. The reproducibility of AFLP for seven primer
combinations was investigated by repeated analysis of all steps from DNA isolation to data scoring. For 5088 comparisons,
the overall reproducibility was 97.6%. Robustness to genotyping errors was investigated by including an artificial F1 (1 : 1 DNA mixture) of two sugarbeet lines in the screen for polymorphisms. For the 3160 cases of polymorphism between the
two lines, 0.2% genotyping errors were found. The general reliability and usefulness of AFLP markers are discussed in relation
to the results obtained.
Identifying adaptive genetic variation is a challenging task, in particular in non-model species for which genomic information is still limited or absent. Here, we studied distribution patterns of amplified fragment length polymorphisms (AFLPs) in response to environmental variation, in 13 alpine plant species consistently sampled across the entire European Alps. Multiple linear regressions were performed between AFLP allele frequencies per site as dependent variables and two categories of independent variables, namely Moran's eigenvector map MEM variables (to account for spatial and unaccounted environmental variation, and historical demographic processes) and environmental variables. These associations allowed the identification of 153 loci of ecological relevance. Univariate regressions between allele frequency and each environmental factor further showed that loci of ecological relevance were mainly correlated with MEM variables. We found that precipitation and temperature were the best environmental predictors, whereas topographic factors were rarely involved in environmental associations. Climatic factors, subject to rapid variation as a result of the current global warming, are known to strongly influence the fate of alpine plants. Our study shows, for the first time for a large number of species, that the same environmental variables are drivers of plant adaptation at the scale of a whole biome, here the European Alps.
Pulsatilla vulgaris Mill. (Ranunculaceae) is a rare and rapidly declining grassland community species that was once widespread at a time when Central Germany was covered by steppe vegetation. Through the course of this study, the patterns of random-amplified polymorphic DNA (RAPD) variation among 11 populations of varying size were analysed to assess any possible local differentiation, in relation to spatial isolation, resulting from random genetic drift brought on by reduced population size and lack of migration between geographically isolated populations. Following results attained from methods including: multivariate analysis based on asymmetric Soerensen similarity, φST-statistics, and analysis of molecular variance, we were able to conclude that there is a high within-population variability (84.4%) and a weak, but significant, differentiation among populations (φST=0.17). A matrix correlation between genetic and geographical distances revealed that geographical differentiation was reflected in the RAPD profile (Mantel test: r=0.47,p=0.002). Further significant correlations were noted between population size and both percentage of polymorphic loci (p=0.02) and genetic diversity (p=0.03). An additional analysis of seed production showed that mean seed set, seed number, and mean seed mass per population could be attributed to differences in population size, whereas only seed mass was related to genetic variation.