Search

For conservation managers, it is important to know whether landscape changes lead to increasing or decreasing gene flow. Although the discipline of landscape genetics assesses the influence of landscape elements on gene flow, no studies have yet used landscape-genetic models to predict gene flow resulting from landscape change. A species that has already been severely affected by landscape change is the large marsh grasshopper (Stethophyma grossum), which inhabits moist areas in fragmented agricultural landscapes in Switzerland. From transects drawn between all population pairs within maximum dispersal distance (< 3 km), we calculated several measures of landscape composition as well as some measures of habitat configuration. Additionally, a complete sampling of all populations in our study area allowed incorporating measures of population topology. These measures together with the landscape metrics formed the predictor variables in linear models with gene flow as response variable (F(ST) and mean pairwise assignment probability). With a modified leave-one-out cross-validation approach, we selected the model with the highest predictive accuracy. With this model, we predicted gene flow under several landscape-change scenarios, which simulated construction, rezoning or restoration projects, and the establishment of a new population. For some landscape-change scenarios, significant increase or decrease in gene flow was predicted, while for others little change was forecast. Furthermore, we found that the measures of population topology strongly increase model fit in landscape genetic analysis. This study demonstrates the use of predictive landscape-genetic models in conservation and landscape planning.

Directed dispersal by animal vectors has been found to have large effects on the structure and dynamics of plant populations adapted to frugivory. Yet, empirical data are lacking on the potential of directed dispersal by rotational grazing of domestic animals to mediate gene flow across the landscape. Here, we investigated the potential effect of large-flock shepherding on landscape-scale genetic structure in the calcareous grassland plant Dianthus carthusianorum, whose seeds lack morphological adaptations to dispersal to animals or wind. We found a significant pattern of genetic structure differentiating population within grazed patches of three nonoverlapping shepherding systems and populations of ungrazed patches. Among ungrazed patches, we found a strong and significant effect of isolation by distance (r = 0.56). In contrast, genetic distance between grazed patches within the same herding system was unrelated to geographical distance but significantly related to distance along shepherding routes (r = 0.44). This latter effect of connectivity along shepherding routes suggests that gene flow is spatially restricted occurring mostly between adjacent populations. While this study used nuclear markers that integrate gene flow by pollen and seed, the significant difference in the genetic structure between ungrazed patches and patches connected by large-flock shepherding indicates the potential of directed seed dispersal by sheep across the landscape., (© 2013 John Wiley & Sons Ltd.)

Landscape genetics has seen rapid growth in number of publications since the term was coined in 2003. An extensive literature search from 1998 to 2008 using keywords associated with landscape genetics yielded 655 articles encompassing a vast array of study organisms, study designs and methodology. These publications were screened to identify 174 studies that explicitly incorporated at least one landscape variable with genetic data. We systematically reviewed this set of papers to assess taxonomic and temporal trends in: (i) geographic regions studied; (ii) types of questions addressed; (iii) molecular markers used; (iv) statistical analyses used; and (v) types and nature of spatial data used. Overall, studies have occurred in geographic regions proximal to developed countries and more commonly in terrestrial vs. aquatic habitats. Questions most often focused on effects of barriers and/or landscape variables on gene flow. The most commonly used molecular markers were microsatellites and amplified fragment length polymorphism (AFLPs), with AFLPs used more frequently in plants than animals. Analysis methods were dominated by Mantel and assignment tests. We also assessed differences among journals to evaluate the uniformity of reporting and publication standards. Few studies presented an explicit study design or explicit descriptions of spatial extent. While some landscape variables such as topographic relief affected most species studied, effects were not universal, and some species appeared unaffected by the landscape. Effects of habitat fragmentation were mixed, with some species altering movement paths and others unaffected. Taken together, although some generalities emerged regarding effects of specific landscape variables, results varied, thereby reinforcing the need for species-specific work. We conclude by: highlighting gaps in knowledge and methodology, providing guidelines to authors and reviewers of landscape genetics studies, and suggesting promising future directions of inquiry.

Landscape features exist at multiple spatial and temporal scales, and these naturally affect spatial genetic structure and our ability to make inferences about gene flow. This article discusses how decisions about sampling of genotypes (including choices about analytical methods and genetic markers) should be driven by the scale of spatial genetic structure, the time frame that landscape features have existed in their current state, and all aspects of a species' life history. Researchers should use caution when making inferences about gene flow, especially when the spatial extent of the study area is limited. The scale of sampling of the landscape introduces different features that may affect gene flow. Sampling grain should be smaller than the average home-range size or dispersal distance of the study organism and, for raster data, existing research suggests that simplifying the thematic resolution into discrete classes may result in low power to detect effects on gene flow. Therefore, the methods used to characterize the landscape between sampling sites may be a primary determinant for the spatial scale at which analytical results are applicable, and the use of only one sampling scale for a particular statistical method may lead researchers to overlook important factors affecting gene flow. The particular analytical technique used to correlate landscape data and genetic data may also influence results; common landscape-genetic methods may not be suitable for all study systems, particularly when the rate of landscape change is faster than can be resolved by common molecular markers.

Natural genetic breaks may indicate limitations to gene flow or the presence of contact zones of previously isolated populations. Molecular evidence suggests that genetic breaks have aggregated in distinct geographical areas. We propose a new application of well-established statistical methods for analysing multilocus genetic data to identify intraspecific genetic breaks. The methodological approach combines Bayesian clustering with a spatially explicit maximum-difference algorithm to visualize and quantify breaks between clusters. We used amplified fragment length polymorphism data of two co-distributed, silicicolous alpine plant species, Geum montanum and Geum reptans, exhaustively sampled on a consistent, regular grid over their entire range of the European Alps and the Carpathians. We found a distinct and highly similar allocation of genetic breaks in both species. The pattern of breaks did not conform to scenarios of glacial refugial survival, alternatively in peripheral refugia or on nunataks, as expected because of the species' ecologies (late-successional low alpine vs. early-successional high alpine). Our findings rather substantiated the postulate of a general pattern of genetic breaks in alpine plants and corresponded well with biogeographical regions formerly described. Our approach could serve as a tool not only for landscape genetics and comparative phylogeography, but also for floristics or faunistics to compare biogeographic with phylogeographic breaks.

Black poplar ( Populus nigra L.) is a keystone species of riparian ecosystems in large parts of Europe. While adult black poplars were thoroughly surveyed across Europe, there is much less information about the species’ natural regeneration. As the cultivar Populus x canadensis often grows in the surroundings of black poplar stands, introgression is being discussed as threat for black poplar rejuvenation. In the present study, we identified the proportion of black poplar seedlings and juvenile trees at three sites in Switzerland as compared to hybrid poplar offspring growing at the same sites. Taxon identification was based on a combination of a chloroplast and two nuclear markers. Using SSR markers, we estimated the extent of clonality of adult and juvenile trees, estimated genetic diversity of all age classes and determined the proportion of gene flow from outside the local stand. We found different proportions of black poplar regeneration at our three study sites, ranging from no hybrid offspring in Valais, where most adult black poplars relative to adult P . x canadensis occurred, to 90% hybrid seedlings in Thurgau, where the black poplar stand consisted of only four individuals, surrounded by a large number of P. x canadensis. The extent of clonality was generally low, as we identified less than 10% recurrent genotypes among juveniles and adults. We found high numbers of alleles and high heterozygosity in all populations. Substantial gene flow from outside the local stands could be detected in two study sites, indicating that black poplar at least partly overcomes the current degree of fragmentation in Switzerland. [ABSTRACT FROM AUTHOR]

Dispersal is an important process for any organism, but especially for endangered species in fragmented landscapes. To enhance the dispersal of a certain species, connectivity measures are implemented, which require knowledge on the species' dispersal behaviour and habitat. It is often assumed, that the preferred reproductive habitat of a species is also used as the main dispersal habitat. Although this assumption has often been confirmed, there are also cases where it has been disproved., With a combination of a mark-resight study and genetic analysis conducted in a fragmented agricultural landscape in Switzerland, the dispersal habitats of the threatened damselfly Coenagrion mercuriale were analysed for different distance classes. In addition, maximum dispersal distances were estimated., The mark-resight study detected movement over short distances (≤500 m) mainly within the reproductive habitat of C. mercuriale (i.e. streams)., In contrast, the genetic study detected both short- and long-distance dispersal. Short-distance dispersal occurred along streams, and discontinuity of streams hindered dispersal. Long-distance dispersal was suggested to happen along more or less straight lines and crossing agricultural land. Genetic analysis also showed that populations were well connected and that few individuals dispersed over larger distances (≤4500 m)., Our study showed that connected reproductive habitat enhanced short-distance dispersal in C. mercuriale. Although short-distance dispersal occurred frequently, long-distance dispersal was rare, but important to connect more isolated populations. Therefore, it would be relevant to differentiate between these two dispersal types when planning connectivity measures. [ABSTRACT FROM AUTHOR]

Most landscape genetic studies assess the impact of landscape elements on species' dispersal and gene flow. Many of these studies perform their analysis on all possible population pairs in a study area and do not explicitly consider the effects of spatial scale and population network topology on their results. Here, we examined the effects of spatial scale and population network topology on the outcome of a landscape genetic analysis. Additionally, we tested whether the relevant spatial scale of landscape genetic analysis could be defined by population network topology or by isolation-by-distance ( IBD) patterns. A data set of the wetland grasshopper Stethophyma grossum, collected in a fragmented agricultural landscape, was used to analyse population network topology, IBD patterns and dispersal habitats, using least-cost transect analysis. Landscape genetic analyses neglecting spatial scale and population network topology resulted in models with low fits, with which a most likely dispersal habitat could not be identified. In contrast, analyses considering spatial scale and population network topology resulted in high model fits by restricting landscape genetic analysis to smaller scales (0-3 km) and neighbouring populations, as represented by a Gabriel graph. These models also successfully identified a likely dispersal habitat of S. grossum. The above results suggest that spatial scale and potentially population network topology should be more explicitly considered in future landscape genetic analyses. [ABSTRACT FROM AUTHOR]

The success of ecological restoration is often judged by the number and abundance of species, especially rare ones that have established since restoration. However, the effects of habitat improvement upon connectivity are rarely assessed, although this can readily be performed using modern molecular genetic methods., We evaluated the functional connectivity of populations of a wet grassland plant Lychnis flos-cuculi in an intensively managed agricultural landscape in Switzerland. One third of the study populations had been recently restored by sowing wildflower seed mixtures, while all other populations were of natural origin. We used assignment tests to identify first-generation migrants and to estimate recent patterns of gene flow among the populations of L. flos-cuculi., Assignment tests revealed higher levels of recent gene flow among natural populations of L. flos-cuculi than between sown and natural populations. Most probably, this result simply reflected the formerly good connectivity of natural populations in the study landscape., We detected a few first-generation migrants between sown and natural populations and among natural populations, suggesting that functional connectivity was now rather restricted. Migration among sown and natural populations was more likely to occur when natural and sown populations were nearby and when source populations were large., Synthesis and applications. We demonstrated that genetic methods offer a valuable tool for examining the effects of restoration measures on functional connectivity of plant populations. The connectivity of wet grasslands is likely to be best enhanced by establishing a relatively dense network of large habitat patches. [ABSTRACT FROM AUTHOR]

Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Landscape genetics aims to assess the effect of the landscape on intraspecific genetic structure. To quantify interdeme landscape structure, landscape genetics primarily uses landscape resistance surfaces (RSs) and least-cost paths or straight-line transects. However, both approaches have drawbacks. Parameterization of RSs is a subjective process, and least-cost paths represent a single migration route. A transect-based approach might oversimplify migration patterns by assuming rectilinear migration. To overcome these limitations, we combined these two methods in a new landscape genetic approach: least-cost transect analysis (LCTA). Habitat-matrix RSs were used to create least-cost paths, which were subsequently buffered to form transects in which the abundance of several landscape elements was quantified. To maintain objectivity, this analysis was repeated so that each landscape element was in turn regarded as migration habitat. The relationship between explanatory variables and genetic distances was then assessed following a mixed modelling approach to account for the nonindependence of values in distance matrices. Subsequently, the best fitting model was selected using the statistic. We applied LCTA and the mixed modelling approach to an empirical genetic dataset on the endangered damselfly, Coenagrion mercuriale. We compared the results to those obtained from traditional least-cost, effective and resistance distance analysis. We showed that LCTA is an objective approach that identifies both the most probable migration habitat and landscape elements that either inhibit or facilitate gene flow. Although we believe the statistical approach to be an improvement for the analysis of distance matrices in landscape genetics, more stringent testing is needed. [ABSTRACT FROM AUTHOR]

1. Landscape genetic approaches were used to assess functional connectivity of populations of the endangered damselfly Coenagrion mercuriale in a fragmented agricultural landscape in Switzerland. Spatial genetic clustering methods combined with interpolation by kriging and landscape genetic corridor analysis were applied to identify landscape elements that enhance or hinder dispersal and gene flow. 2. Spatial genetic clustering analysis divided the sampled populations into a northern and a southern genetic group. The boundary between the two groups coincided with a hill ridge intersecting the study area. Landscape corridor analysis identified five landscape elements that significantly affected gene flow. Elevation change, Euclidian distance, patches of forest and flowing waterbodies acted as barriers, whereas open agricultural land enhanced gene flow between populations of C. mercuriale. 3. This study showed that movement of C. mercuriale was not restricted to its preferred habitat (i.e. streams). Populations linked via continuous open agricultural land were functionally well connected if they were not more than about 1.5-2 km apart. In contrast, substantial elevation change and larger forest patches separated populations. These findings may serve as a basis to define conservation units and should be considered when planning connectivity measures, such as determining the locations of stepping stones, or the restoration of streams. [ABSTRACT FROM AUTHOR]

Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Identifying landscape elements that influence gene flow and migration in wild species is the current main topic of landscape genetics. Most landscape genetic studies infer gene flow and migration from genetic distances among populations or individuals and statistically relate these measurements to landscape composition and configuration. This approach assumes symmetrical gene flow between pairs of populations. Such an assumption, however, will often be violated, especially in source-sink systems. Source populations provide more emigrants than they receive immigrants, and sink populations get many immigrants, but release few emigrants. Source-sink dynamics cannot be explored using common landscape genetic approaches relying on genetic distances. In this issue of Molecular Ecology, Andreasen et al. () apply an alternative approach allowing them to infer asymmetrical migration. They use a Bayesian assignment test among objectively defined populations of mountain lions ( Puma concolor) in western USA to estimate recent and directional migration rates. The study shows that an area with a high amount of wildlife refuges and low hunting pressure harbours a source population for mountain lion dispersal, while areas with high hunting pressures form sink populations; a result helpful in making informed decisions in conservation management. [ABSTRACT FROM AUTHOR]

Premise of the study: Polymorphic microsatellite markers were developed for the inbred alpine perennial plant Arabis alpina to infer life-history parameters and measure patterns of contemporary gene flow within populations. Methods and Results : Using the 454 pyrosequencing technique, 19 microsatellite primer sets were developed for A. alpina . The primer sets were tested on 60 individuals sampled from three sub-populations in the Swiss Alps. The primers amplified di- and trinucleotide repeats with two to five alleles per locus. Conclusions: Previous attempts to isolate microsatellite loci in A. alpina using enrichment libraries and cross-amplification were difficult and produced an insufficient number of polymorphic microsatellite loci. In contrast, next-generation sequencing technology was successful in identifying microsatellite repeats in A. alpina. These newly developed microsatellite primers will be useful to further develop A. alpina into a model species for eco-genomic studies. [ABSTRACT FROM AUTHOR]

Abstract: Leucorrhinia caudalis is a rare dragonfly, threatened throughout its European distribution. The species was formerly widespread in the Swiss lowlands, but only a single population remained in the 1980s. However, a spread has recently been observed, with additional ponds being colonised, sometimes at considerable distance. Despite this evidence of recent long-distance dispersal, it is unknown whether L. caudalis regularly moves among ponds or whether this is a rather rare event. A combination of an ecological mark-resight and a population genetic study was applied to investigate contemporary dispersal and the genetic footprint of the recent population history of L. caudalis in Switzerland. DNA for genetic microsatellite analysis was extracted from exuviae. The mark-resight study and the genetic analysis gave congruent results. They showed that L. caudalis is mostly a sedentary species, with only a few contemporary dispersal events over distances up to 5km being observed. The genetic analysis was in agreement with the recent population history of the Swiss populations. The oldest and largest population showed large genetic diversity and acted as source population for the recent spread of L. caudalis in Switzerland. Recurrent gene flow among this source population and close populations caused substantial local genetic variation in the latter, as well as low population differentiation. The two recently founded distant populations (⩾30km distance) were genetically less diverse and highly differentiated. These distant populations and another recently colonised population also expressed signatures of genetic bottlenecks. [ABSTRACT FROM AUTHOR]