High gene flow in epiphytic ferns despite habitat loss and fragmentation

Tropical montane forests suffer from increasing fragmentation and replacement by other types of land-use such as coffee plantations. These processes are known to affect gene flow and genetic structure of plant populations. Epiphytes are particularly vulnerable because they depend on their supporting trees for their entire life-cycle. We compared population genetic structure and genetic diversity derived from AFLP markers of two epiphytic fern species differing in their ability to colonize secondary habitats. One species, Pleopeltis crassinervata, is a successful colonizer of shade trees and isolated trees whereas the other species, Polypodium rhodopleuron, is restricted to forests with anthropogenic separation leading to significant isolation between populations. By far most genetic variation was distributed within rather than among populations in both species, and a genetic admixture analysis did not reveal any clustering. Gene flow exceeded by far the benchmark of one migrant per generation to prevent genetic divergence between populations in both species. Though populations are threatened by habitat loss, long-distance dispersal is likely to support gene flow even between distant populations, which efficiently delays genetic isolation. Consequently, populations may rather be threatened by ecological consequences of habitat loss and fragmentation.     

Genetic equilibrium despite habitat fragmentation in an Afrotropical bird

We examined the effects of habitat fragmentation of the white-starred robin Pogonocichla stellata metapopulation in the Taita Hills archipelago, a hotspot for biodiversity which was fragmented approximately 40 years ago. Using seven microsatellite markers, we analysed the robin's genetic structure and tested for equilibrium between migration and drift (testing the probability of decreased dispersal) as well as between mutation and drift (test for recent reduction in effective population size, i.e. bottlenecks). This metapopulation was found to retain relatively high levels of genetic variability (H(E) between 0.63 and 0.71) and to be in migration-drift equilibrium, suggesting that increased isolation between fragments did not have much effect on the dispersal between them. Furthermore, this equilibrium test greatly enhanced the interpretation of parameters (e.g. F(ST)) assumed to have reached an equilibrium value. In contrast to previous findings on the related and sympatric Taita thrush Turdus helleri (which is critically endangered), there were no indications for recent bottlenecks in any of the robin subpopulations. This difference can be attributed to the higher dispersal capacity of the robin compared with the thrush (deduced from both the genetic and capture-recapture data). Our results stress the importance of sustained dispersal for species conservation.     

The impact of habitat loss and fragmentation on genetic drift and fixation time

In this study, a simple genetic model is integrated with an established method from landscape ecology to investigate the effect of habitat geometry and availability on genetic drift. Previous ecological modelling has identified a sharp threshold in habitat availability for species' persistence, beyond which the species rapidly becomes extinct. This study demonstrates the existence of a similar threshold for fixation time of selectively neutral genotypes by genetic drift, the location of which is determined by habitat shape and spatial correlation of habitat loss. Time to fixation is greater for habitats if they are long and thin rather than square. Despite reductions in population size due to habitat loss, fixation time remains relatively constant until a pre-threshold value, beyond which there is often a substantial increase in time to fixation. Further habitat loss results in the percolation threshold being reached and beyond this point the time to fixation decreases very rapidly. This study reveals a complex relationship between habitat availability, habitat geometry and the process of genetic drift. Possible implications of our results for conservation are discussed. Further work is required to improve our understanding of the interaction between evolutionary, ecological and landscape processes.     

Short-term genetic consequences of habitat loss and fragmentation for the neotropical palm Oenocarpus bataua

Habitat loss and fragmentation may impact animal-mediated dispersal of seed and pollen, and a key question is how the genetic attributes of plant populations respond to these changes. Theory predicts that genetic diversity may be less sensitive to such disruptions in the short term, whereas inbreeding and genetic structure may respond more strongly. However, results from studies to date vary in relation to species, context and the parameter being assessed, triggering calls for more empirical studies, especially from the tropics, where plant–animal dispersal mutualisms are both disproportionately common and at risk. We compared the genetic characteristics of adults and recruits in a long-lived palm Oenocarpus bataua in a recently fragmented landscape (<2 generations) in northwest Ecuador using a suite of 10 polymorphic microsatellite markers. We sampled individuals from six forest fragments and one nearby continuous forest. Our goal was to assess short-term consequences of fragmentation, with a focus on how well empirical data from this system follow theoretical expectations. Mostly congruent with predictions, we found stronger genetic differentiation and fine-scale spatial genetic structure among recruits in fragments compared with recruits in continuous forest, but we did not record differences in genetic diversity or inbreeding, nor did we record any differences between adults in fragments and adults in continuous forest. Our findings suggest that genetic characteristics of populations vary in their sensitivity to change in response to habitat loss and fragmentation, and that fine-scale spatial genetic structure may be a particularly useful indicator of genetic change in recently fragmented landscapes.     

Bayesian analysis of genetic differentiation between populations

We introduce a Bayesian method for estimating hidden population substructure using multilocus molecular markers and geographical information provided by the sampling design. The joint posterior distribution of the substructure and allele frequencies of the respective populations is available in an analytical form when the number of populations is small, whereas an approximation based on a Markov chain Monte Carlo simulation approach can be obtained for a moderate or large number of populations. Using the joint posterior distribution, posteriors can also be derived for any evolutionary population parameters, such as the traditional fixation indices. A major advantage compared to most earlier methods is that the number of populations is treated here as an unknown parameter. What is traditionally considered as two genetically distinct populations, either recently founded or connected by considerable gene flow, is here considered as one panmictic population with a certain probability based on marker data and prior information. Analyses of previously published data on the Moroccan argan tree (Argania spinosa) and of simulated data sets suggest that our method is capable of estimating a population substructure, while not artificially enforcing a substructure when it does not exist. The software (BAPS) used for the computations is freely available from http://www.rni.helsinki.fi/~mjs.     

The scale of genetic differentiation in the Dunes Sagebrush-Lizard (Sceloporus arenicolus), an endemic habitat specialist

The Dunes Sagebrush-Lizard (Sceloporus arenicolus) is a North American species endemic to sand-shinnery oak habitats of the Mescalero and Monahans sand dunes in eastern New Mexico and western Texas. This lizard is listed as Endangered in New Mexico and exhibits habitat specificity at several geographic scales. Dunes Sagebrush-Lizards are only found in topographically complex shinnery oak (Quercus havardii) dominated landscapes within their small geographic distribution and are not found in surrounding human-altered landscapes. Within suitable sand-shinnery oak habitat, individuals predominantly occupy non-vegetated sand dune blowouts and utilize blowouts with particular physical characteristics due to thermoregulatory, reproduction, and foraging requirements. Here, we examined historical and contemporary patterns of genetic differentiation with respect to the current distribution of suitable habitat at multiple spatial scales using mitochondrial DNA sequences and microsatellite data from individuals throughout the entire range. We found three genetic clusters of individuals generally concordant with geographic regions and low sequence divergence at mitochondrial loci suggesting a recent origin of these populations. We also found high levels of genetic structure at microsatellite loci among populations within each of these groups indicating restricted gene flow at intermediate scales. Despite high habitat specificity, we did not detect genetic structure among sand blowouts at finer spatial scales. Within each population, matrices comprised of both sand blowouts and vegetated shinnery oak patches are necessary for genetic connectivity, but the fine scale spatial arrangement of blowouts may not be as critical. We discuss our results with respect to the scale of landscape heterogeneity and habitat connectivity and consider the conservation implications for this threatened taxon.     

Effects of habitat fragmentation and black-tailed prairie dogs on urban avian diversity

Urbanization and habitat fragmentation have the potential to influence bird communities. In addition, these phenomena, as well as ongoing lethal control measures, have also greatly reduced the range of the black-tailed prairie dog (Cynomys ludovicianus) since the beginning of the 20th century. Although prairie dogs are highly interactive species that can influence avian communities, few studies have investigated whether these interactions persist in urban settings. Our goal was to investigate the relative impacts of habitat fragmentation and prairie dogs on bird communities within an urban matrix. We performed bird surveys on 20 habitat fragments (10 colonized by prairie dogs, 10 uncolonized by prairie dogs) distributed throughout the Denver metropolitan area, and calculated Shannon–Weiner diversity and richness of all birds and native species, as well as total counts of grassland birds and raptors. Diversity, richness, and counts of many species increased with increasing fragment connectivity, and decreased on fragments isolated for longer periods of time. Avian diversity and richness did not differ between fragments with and without prairie dogs, suggesting that this element of the ecological role of prairie dogs is not fully retained in urban habitat. Future studies of the role of prairie dogs as keystone species in urban systems should include other taxa as well as consider the influence of the urban matrix surrounding prairie dog habitat. Our results emphasize that conservation of urban avian diversity should focus on landscape connectivity as well as local habitat features.     

An endangered flightless grasshopper with strong genetic structure maintains population genetic variation despite extensive habitat loss

Conservation research is dominated by vertebrate examples but the shorter generation times and high local population sizes of invertebrates may lead to very different management strategies, particularly for species with low movement rates. Here we investigate the genetic structure of an endangered flightless grasshopper, Keyacris scurra, which was used in classical evolutionary studies in the 1960s. It had a wide distribution across New South Wales (NSW) and Victoria in pre‐European times but has now become threatened because of land clearing for agriculture and other activities. We revisited remnant sites of K. scurra, with populations now restricted to only one area in Victoria and a few small patches in NSW and the Australian Capital Territory (ACT). Using DArtseq to generate SNP markers as well as mtDNA sequence data, we show that the remaining Victorian populations in an isolated valley are genetically distinct from the NSW populations and that all populations tend to be genetically unique, with large F _ST values up to 0.8 being detected for the SNP datasets. We also find that, with one notable exception, the NSW/ACT populations separate genetically into previously described chromosomal races (2n = 15 vs. 2n = 17). Isolation by distance was detected across both the SNP and mtDNA datasets, and there was substantial differentiation within chromosomal races. Genetic diversity as measured by heterozygosity was not correlated with the size of remaining habitat where the populations were found, with high variation present in some remnant cemetery sites. However, inbreeding correlated negatively with estimated habitat size at 25–500 m patch radius. These findings emphasize the importance of small habitat areas in conserving genetic variation in such species with low mobility, and they highlight populations suitable for future translocation efforts.     

How fire interacts with habitat loss and fragmentation

Biodiversity faces many threats and these can interact to produce outcomes that may not be predicted by considering their effects in isolation. Habitat loss and fragmentation (hereafter ‘fragmentation’) and altered fire regimes are important threats to biodiversity, but their interactions have not been systematically evaluated across the globe. In this comprehensive synthesis, including 162 papers which provided 274 cases, we offer a framework for understanding how fire interacts with fragmentation. Fire and fragmentation interact in three main ways: (i) fire influences fragmentation (59% of 274 cases), where fire either destroys and fragments habitat or creates and connects habitat; (ii) fragmentation influences fire (25% of cases) where, after habitat is reduced in area and fragmented, fire in the landscape is subsequently altered because people suppress or ignite fires, or there is increased edge flammability or increased obstruction to fire spread; and (iii) where the two do not influence each other, but fire interacts with fragmentation to affect responses like species richness, abundance and extinction risk (16% of cases). Where fire and fragmentation do influence each other, feedback loops are possible that can lead to ecosystem conversion (e.g. forest to grassland). This is a well-documented threat in the tropics but with potential also to be important elsewhere. Fire interacts with fragmentation through scale-specific mechanisms: fire creates edges and drives edge effects; fire alters patch quality; and fire alters landscape-scale connectivity. We found only 12 cases in which studies reported the four essential strata for testing a full interaction, which were fragmented and unfragmented landscapes that both span contrasting fire histories, such as recently burnt and long unburnt vegetation. Simulation and empirical studies show that fire and fragmentation can interact synergistically, multiplicatively, antagonistically or additively. These cases highlight a key reason why understanding interactions is so important: when fire and fragmentation act together they can cause local extinctions, even when their separate effects are neutral. Whether fire–fragmentation interactions benefit or disadvantage species is often determined by the species' preferred successional stage. Adding fire to landscapes generally benefits early-successional plant and animal species, whereas it is detrimental to late-successional species. However, when fire interacts with fragmentation, the direction of effect of fire on a species could be reversed from the effect expected by successional preferences. Adding fire to fragmented landscapes can be detrimental for species that would normally co-exist with fire, because species may no longer be able to disperse to their preferred successional stage. Further, animals may be attracted to particular successional stages leading to unexpected responses to fragmentation, such as higher abundance in more isolated unburnt patches. Growing human populations and increasing resource consumption suggest that fragmentation trends will worsen over coming years. Combined with increasing alteration of fire regimes due to climate change and human-caused ignitions, interactions of fire with fragmentation are likely to become more common. Our new framework paves the way for developing a better understanding of how fire interacts with fragmentation, and for conserving biodiversity in the face of these emerging challenges.     

生境片断化对植物种群遗传结构的影响及植物遗传多样性保护

生境片断化是指大而连续的生境变成空间隔离的小种群的现象。生境片断化对植物种群遗传效应包括生境片断化过程中的取样效应及其后的小种群效应（遗传漂变、近交等）。理论研究表明,生境片断化后,植物种群的遗传变异程度将降低,而残留的小种群间的遗传分化程度将升高。然而对一些植物的研究表明,生境片断化对植物种群的遗传效应要受其他一些因素的影响,如世代长度、片断化时间、片断种群的大小、基因流的改变等。最后,针对生境     

Recent habitat fragmentation due to roads can lead to significant genetic differentiation in an abundant flightless ground beetle

Although habitat fragmentation is suspected to pose a major threat to biodiversity, its impact on abundant invertebrate species has been little investigated. We assessed the genetic population structure of the flightless ground beetle Abax parallelepipedus in a forest fragmented by two main roads and a highway using five microsatellite loci. We detected low levels of genetic differentiation, which was concordant with the high population densities of 632-1707 individuals/ha estimated with a mark-recapture method. A Mantel test detected a highly significant increase of pairwise F(ST)-values with the number of roads between sampling locations. As expected, the most pronounced effect of the isolation due to roads was observed in the sample from the smallest fragment (highway exit loop), which was differentiated significantly from most other locations. However, no signs of a recent bottleneck or a loss of genetic variability were detected in this population, indicating a still relatively large effective population size (N(e)). Computer simulations confirmed that the observed F(ST)-values were indeed compatible with a N(e) of a few hundred individuals in this fragment, assuming strong or absolute isolation since the construction of the roads. We discuss the implications of our findings for the conservation of abundant but poorly dispersing species in fragmented habitats.     

Low genetic differentiation among populations ofArabis serrata (Brassicaceae) along an altitudinal gradient

We investigated the extent of genetic differentiation among populations of fujihatazao,Arabis serrata along an altitudinal gradient at Mt. Fuji in Shizuoka Prefecture. This species is a perennial plant, widely distributed in Japan forming small isolated populations. However, at Mt. Fuji, this species constitutes a large population distributed from 1440 to 2400 m altitude. A total of 411 individuals were sampled from ten subpopulations. Eighteen loci were detected on eleven enzyme systems. Eleven loci were monomorphic and seven loci were polymorphic with a mean of 2.11 alleles per loci. Nei's genetic distance (mean 0.01) and genetic identity (mean 0.968) were very similar among populations indicating a low genetic differentiation. The total genetic diversity (H _T ) estimated for the polymorphic loci was, in average, 0.396. The mean gene differentiation (G_ST=0.091) was very low. Gene frequency of seven polymorphic loci was analyzed by spatial autocorrelation methods based on Moran's indexes. Only Pgi-3 exhibited a significant negative autocorrelation (−0.160;P<0.05); other loci values ranged from −0.134 to 0.027. Gene flow estimated by indirect methods varied between genes but most of the values were high (meanNm=20.8) suggesting that subpopulations at different altitudes are probably connected. Despite plants at different altitudes present different ecological traits (e.g., differences in phenology, growth and reproductive traits), subpopulations ofA. serrata are still low differentiated, at least for the loci studied. This may be explained by the recent origin of some habitats (e.g., second crater and surrounded areas) in this locality.     

The effect of habitat fragmentation on the genetic structure of a top predator: loss of diversity and high differentiation among remnant populations of Atlantic Forest jaguars (Panthera onca)

Habitat fragmentation may disrupt original patterns of gene flow and lead to drift-induced differentiation among local population units. Top predators such as the jaguar may be particularly susceptible to this effect, given their low population densities, leading to small effective sizes in local fragments. On the other hand, the jaguar's high dispersal capabilities and relatively long generation time might counteract this process, slowing the effect of drift on local populations over the time frame of decades or centuries. In this study, we have addressed this issue by investigating the genetic structure of jaguars in a recently fragmented Atlantic Forest region, aiming to test whether loss of diversity and differentiation among local populations are detectable, and whether they can be attributed to the recent effect of drift. We used 13 microsatellite loci to characterize the genetic diversity present in four remnant populations, and observed marked differentiation among them, with evidence of recent allelic loss in local areas. Although some migrant and admixed individuals were identified, our results indicate that recent large-scale habitat removal and fragmentation among these areas has been sufficiently strong to promote differentiation induced by drift and loss of alleles at each site. Low estimated effective sizes supported the inference that genetic drift could have caused this effect within a short time frame. These results indicate that jaguars' ability to effectively disperse across the human-dominated landscapes that separate the fragments is currently very limited, and that each fragment contains a small, isolated population that is already suffering from the effects of genetic drift.     

生境破碎化对动物种群存活的影响

生境破碎是生物多样性下降的主要原因之一。通常以岛屿生物地理学、异质种群生物学和景观生态学的理论来解释不同空间尺度中生境破碎化的生态学效应。生境破碎化引起面积效应、隔离效应和边缘效应。这些效应通过影响动物种群的绝灭阈值、分布和多度、种间关系以及生态系统过程,最终影响动物种群的存活。野外研究表明,破碎化对动物的影响,因物种、生境类型和地理区域不同而有所变化,因此,预测物种在破碎生境中的存活比较困难。研究热点集中于：确定生境面积损失和生境斑块的空间格局对破碎景观中物种绝灭的相对影响,破碎景观中物种的适宜生境比例和绝灭阈值,异质种群动态以及生态系统的生态过程。随着3S技术的发展,生境破碎化模型趋于复杂,而发展有效的模型和验证模型将成为一项富有挑战性的任务。     

Conservation genetics of an endemic from the Mediterranean Basin: high genetic differentiation but no genetic diversity loss from the last populations of the Sicilian Grape Hyacinth Leopoldia gussonei

The Mediterranean Basin is a biodiversity hotspot, housing >11.000 narrowly endemic plant species, many of which are declining due to mass tourism and agricultural intensification. To investigate the genetic resource impacts of ongoing habitat loss and degradation, we characterized the genetic variation in the last known populations of Leopoldia gussonei, a self-compatible endangered Sicilian Grape Hyacinth numbering less than 3,000 remaining individuals, using AFLP. Results demonstrated significant genome-wide genetic differentiation among all extant populations (Φ_ST = 0.05–0.56), and genetic clustering according to geographic location. Gene diversity was fairly constant across population (mean H_E = 0.13) and was neither affected by current population size nor by spatial isolation. Vegetation analysis showed the presence of known invasive weeds in a quarter of the populations, but we found no relation between genetic diversity and plant community composition. The marked genetic differences among populations and the profusion of rare and private alleles indicate that any further population loss will lead to significant losses of genetic diversity. Conservation efforts should therefore focus on the preservation of all sites where L. gussonei still occurs, yet the deliberate introduction of diverse material into the smallest populations seems unneeded as clonality likely mitigated genetic drift effects thus far. More generally, our findings support the view that endemic plant species with a narrow ecological amplitude, as many specialists in Mediterranean coastal ecosystems, are highly genetically differentiated and that conservation of their genetic diversity requires preservation of most, if not all of their extant populations.     

Estimating plant migration rates under habitat loss and fragmentation

Changes in the global environment are modifying the geographical locations of habitats suitable for plant growth. The capacity of plants to migrate to sites of suitable environmental quality will strongly influence future distributions of plant diversity. However, it is not well understood how rates of plant migration are influenced by the habitat loss and habitat fragmentation that characterise contemporary landscapes. In this study we develop a model that can predict migration rates in both intact landscapes (potential migration rate) and in fragmented landscapes (realised migration rates). Migration rates in fragmented landscapes might be slower for many reasons. In this study we focus on two, non‐exclusive reasons. First, the processes that move seeds may break down in fragmented landscapes causing seeds to be dispersed shorter distances. Second, in fragmented landscapes some proportion of seeds will not be deposited in habitats suitable for recruitment. We describe the breakdown of dispersal processes as a competing risk between the factors influencing dispersal in intact landscapes and the factors that may disrupt dispersal processes in fragmented landscapes. We show how the parameters that influence dispersal in fragmented landscapes can be estimated, and how these estimates can be used to forecast migration rates using an integrodifference equation (IDE). The forecasts of the IDE described the effects of reduced dispersal distances adequately. However, the IDE produced biased estimates of the effects of a reduction in plant habitat on migration rates. Model analyses showed that, although we can expect realised migration rates to be lower than potential migration rates, we can also expect the sensitivity of migration rate to habitat loss to vary. In addition, simulations showed that the qualitative nature of the responses of migration rate to habitat loss were variable – some model species responded non‐linearly to habitat loss, others responded linearly. While our method provides guidelines for empirical data collection and model parameterisation, we recognise that obtaining these data will be challenging.     

Phenotypic and genetic differentiation between native and introduced plant populations

Plant invasions often involve rapid evolutionary change. Founder effects, hybridization, and adaptation to novel environments cause genetic differentiation between native and introduced populations and may contribute to the success of invaders. An influential idea in this context has been the Evolution of Increased Competitive Ability (EICA) hypothesis. It proposes that after enemy release plants rapidly evolve to be less defended but more competitive, thereby increasing plant vigour in introduced populations. To detect evolutionary change in invaders, comparative studies of native versus introduced populations are needed. Here, we review the current empirical evidence from: (1) comparisons of phenotypic variation in natural populations; (2) comparisons of molecular variation with neutral genetic markers; (3) comparisons of quantitative genetic variation in a common environment; and (4) comparisons of phenotypic plasticity across different environments. Field data suggest that increased vigour and reduced herbivory are common in introduced plant populations. In molecular studies, the genetic diversity of introduced populations was not consistently different from that of native populations. Multiple introductions of invasive plants appear to be the rule rather than the exception. In tests of the EICA hypothesis in a common environment, several found increased growth or decreased resistance in introduced populations. However, few provided a full test of the EICA hypothesis by addressing growth and defence in the same species. Overall, there is reasonable empirical evidence to suggest that genetic differentiation through rapid evolutionary change is important in plant invasions. We discuss conceptual and methodological issues associated with cross-continental comparisons and make recommendations for future research. When testing for EICA, greater emphasis should be put on competitive ability and plant tolerance. Moreover, it is important to address evolutionary change in characteristics other than defence and growth that could play a role in plant invasions.     

Low genetic differentiation between two geographically separated populations of demersal gadiform fishes in the Southern Hemisphere

The distribution patterns of many fishes between the three continents (Africa, Australia, and South America) in the Southern Hemisphere have been uncovered to be influenced by mostly vicariance or historical dispersal. Although some demersal fishes with intercontinental distribution are suggested to be more influenced by current/recent dispersal, few genetic studies have been made for demersal fishes so far. To provide more information for such fishes, genetic divergence was analyzed for two pairs of gadiform species and subspecies distributed around Australasia and South America: the blue grenadier, Macruronus novaezelandiae (from New Zealand) and the Patagonian grenadier, M. magellanicus (from South America) as well as two subspecies of the southern blue whiting, Micromesistius australis pallidus (from New Zealand) and M. a. australis (from South America). The sequence analyses of two mitochondrial DNA regions showed no divergence between Australasian and South American populations of the grenadiers and the southern blue whiting. The microsatellite DNA analysis also indicated significant but very minimal genetic differentiation between the two geographic populations of each pair. These results imply rather recent separation of the two geographic populations. Current/recent dispersal may be an important common factor for determining the distribution of demersal fishes in the Southern Hemisphere. Nonetheless, low but significant genetic differentiation observed requires treating the two populations of the economically important grenadiers and southern blue whiting, respectively, as different stocks for proper resource management.     

Historic DNA reveals genetic consequences of fragmentation in an endangered,endemic mustard

Understanding how anthropogenic disturbance affects genetic diversity is essential to appropriately incorporating genetic considerations into conservation plans. Unfortunately, we rarely have information about a population’s genetic diversity before it becomes imperiled. Here we reconstruct the historic range of the naturally rare annual mustard Streptanthus glandulosus subsp. niger (Sgn) and use herbarium specimens to quantify pre-disturbance genetic diversity. We compare this to the genetic diversity in the contemporary plant populations and to plants in the seed bank. We conclude that Sgn was recently a single, panmictic population composed of orders of magnitude more plants than exist today but experienced recent and abrupt declines following housing development. Today Sgn persists as two disjunct populations, the larger of which has retained historic levels of diversity although there is a downward trend in all measures. The smaller population has lost 21–28% of the diversity that was present only 50 years ago with an N_e?~?5–16. The contemporary populations have differentiated from each other due to drift. The seed bank contained no novel alleles and had high levels of homozygosity, indicating that it is incapable of providing genetic rescue. This novel combination of hDNA, the aboveground plant population and the seed bank can be used to design high impact conservation plans that appropriately incorporate genetic diversity for this and other imperiled species.

     

Low genetic differentiation among reed warbler Acrocephalus scirpaceus populations across Europe

Migratory birds generally have higher dispersal propensity than resident species and are thus expected to show less genetic differentiation. On the other hand, specific migration patterns may promote genetic structure, such as in situations where migratory divides impede random mixing of individuals. Here we investigated population genetic structure and gene flow patterns in a polytypic passerine, the reed warbler Acrocephalus scirpaceus which shows a migratory divide in central Europe. Using ten polymorphic microsatellite loci and extensive sampling we found low but significant overall genetic differentiation (F_ST=0.013, G’_ST=0.078, D=0.063). Hierarchical F‐statistics and barrier analyses showed low but significant genetic differentiation of Iberian populations, and also slight genetic differences across the migratory divide and between subspecies (A. s. scirpaceus and A. s. fuscus). Three individual‐based Bayesian methods, however, inferred a single genetic unit. Our study thus found low levels of genetic differentiation among reed warbler populations but this genetic differentiation was not pronounced enough to detect a clear population structure using the microsatellite data and no prior information on geographic location of the sampled individuals. This result indicates high levels of gene flow and suggests a possibly recent divergence of European populations after a rapid range expansion. Further studies are necessary to assess divergence times and to reveal the evolutionary history of the reed warbler populations.