Holocene re‐colonisation,central–marginal distribution and habitat specialisation shape population genetic patterns within an Atlantic European grass species

Corynephorus canescens (L.) P.Beauv. is an outbreeding, short‐lived and wind‐dispersed grass species, highly specialised on scattered and disturbance‐dependent habitats of open sandy sites. Its distribution ranges from the Iberian Peninsula over Atlantic regions of Western and Central Europe, but excludes the two other classical European glacial refuge regions on the Apennine and Balkan Peninsulas. To investigate genetic patterns of this uncommon combination of ecological and biogeographic species characteristics, we analysed AFLP variation among 49 populations throughout the European distribution range, expecting (i) patterns of SW European glacial refugia and post‐glacial expansion to the NE; (ii) decreasing genetic diversity from central to marginal populations; and (iii) interacting effects of high gene flow and disturbance‐driven genetic drift. Decreasing genetic diversity from SW to NE and distinct gene pool clustering imply refugia on the Iberian Peninsula and in western France, from where range expansion originated towards the NE. High genetic diversity within and moderate genetic differentiation among populations, and a significant pattern of isolation‐by‐distance indicate a gene flow drift equilibrium within C. canescens, probably due to its restriction to scattered and dynamic habitats and limited dispersal distances. These features, as well as the re‐colonisation history, were found to affect genetic diversity gradients from central to marginal populations. Our study emphasises the need for including the specific ecology into analyses of species (re–)colonisation histories and range centre–margin analyses. To account for discontinuous distributions, new indices of marginality were tested for their suitability in studies of centre–periphery gradients.     

Limited genetic variation and structure in softshell clams (Mya arenaria) across their native and introduced range

To offset declines in commercial landings of the softshell clam, Mya arenaria, resource managers are engaged in extensive stocking of seed clams throughout its range in the northwest Atlantic. Because a mixture of native and introduced stocks can disrupt locally adapted genotypes, we investigated genetic structure in M. arenaria populations across its current distribution to test for patterns of regional differentiation. We sequenced mitochondrial cytochrome oxidase I for a total of 212 individuals from 12 sites in the northwest Atlantic (NW Atlantic), as well as two introduced sites, the northeast Pacific (NE Pacific), and the North Sea Europe (NS Europe). Populations exhibited extremely low genetic variation, with one haplotype dominating (65–100%) at all sites sampled. Despite being introduced in the last 150–400 years, both NE Pacific and NS Europe populations had higher diversity measures than those in the NW Atlantic and both contained private haplotypes at frequencies of 10–27% consistent with their geographic isolation. While significant genetic structure (F _ST = 0.159, P < 0.001) was observed between NW Atlantic and NS Europe, there was no evidence for genetic structure across the pronounced environmental clines of the NW Atlantic. Reduced genetic diversity in mtDNA combined with previous studies reporting reduced genetic diversity in nuclear markers strongly suggests a recent population expansion in the NW Atlantic, a pattern that may result from the retreat of ice sheets during Pleistocene glacial periods. Lack of genetic diversity and regional genetic differentiation suggests that present management strategies for the commercially important softshell clam are unlikely to have a significant impact on the regional distribution of genetic variation, although the possibility of disrupting locally adapted stocks cannot be excluded.     

The fourth paradigm pattern of post-glacial range expansion of European terrestrial species: the phylogeography of the Marbled White butterfly (Satyrinae, Lepidoptera)

Aim Three paradigm patterns of post‐glacial dispersal are known for terrestrial species in Europe. However, the possibility of a fourth arises with the Italian and the Balkan lineages expanding to central Europe and the Iberian one being trapped by the Pyrenees. We test this hypothesis by analysing the molecular biogeography of the Marbled White butterfly. Location Twelve populations distributed over a major part of the European range of Melanargia galathea and M. lachesis. Methods We studied 18 allozyme loci of 403 individuals from 12 populations. Butterflies were sampled in the field, frozen in liquid nitrogen and stored under these conditions until analysis. We used cellulose acetate plates for allozyme electrophoresis. Results We detected three major genetic lineages within the M. galathea/lachesis complex. The M. lachesis sample from the southern Pyrenees was strongly genetically differentiated from M. galathea (F_CT: 0.312). Melanargia galathea splits into two major genetic lineages (F_CT: 0.115), which both were found in post‐glacially invaded regions. The further differentiation within these lineages was comparably low (F_SC: 0.028). The genetic diversity within populations was high compared with other butterfly species. Main conclusions Our findings support the existence of a fourth pattern with only the Iberian lineage not contributing considerably to the post‐glacial colonization of central Europe. Preliminary studies in other butterfly species of dry grasslands support the importance of this pattern possibly representing a fourth paradigm. The high genetic diversity within populations might be one reason for the recently observed expansions at the northern distribution limits.     

Patterns of allozyme variation and clonal diversity in Carex lasiocarpa and C. pellita (Cyperaceae)

We compared genetic variability and clonal diversity in the closely related sedges Carex lasiocarpa and C. pellita using allozyme markers at 12 loci. Both species produce spreading rhizomes, occur in open habitats, and can form large clones; C. lasiocarpa primarily along lakeshores, or in bogs, fens, or marshes, and C. pellita more commonly along riverbanks and ditches or in wet meadows. Polymorphism was high in both species, similar to that of other rhizomatous Carex and to other species with comparable growth forms and life histories. Total gene diversity was higher for C. lasiocarpa (H_T = 0.266) than for C. pellita (H_T = 0.248), but the coefficient of differentiation among populations was lower. Rare alleles usually occurred as heterozygotes rather than homozygotes, and significant deviations from Hardy-Weinberg equilibrium were found at few loci, suggesting that both species are predominantly outcrossing. Mean clone size, diversity, and evenness were not significantly different between the two species, although populations varied from monoclonal to those where nearly every sampled shoot belonged to a different clone. No significant differences in genetic variation or clone size of C. pellita were found when comparisons were made between groups based on climate (warmer vs. cooler) or successional stage (pioneer vs. established). However, within C. lasiocarpa, genetic variability decreased and clone size increased in cooler climates and at established sites.     

Low Atmospheric Nitrogen Loads Lead to Grass Encroachment in Coastal Dunes,but Only on Acid Soils

The impact of atmospheric N-deposition on succession from open sand to dry, lichen-rich, short grassland, and tall grass vegetation dominated by Carex arenaria was surveyed in 19 coastal dune sites along the Baltic Sea. Coastal dunes with acid or slightly calcareous sand reacted differently to atmospheric wet deposition of 5–8 kg N ha⁻¹ y⁻¹. Accelerated acidification, as well as increased growth of Carex and accumulation of organic matter, was observed only at acid sites with pH_NaCl of the parent material below 6.0. At sites with slightly calcareous parent material, increased N-deposition had no effect. A trigger for grass encroachment seems to be high acidification in early successional stages to below pH_NaCl 4.0. Metals like Al or Fe become freely available and may hamper intolerant species. At acid sites, N-mineralization increases with elevated N-deposition, which may further stimulate Carex arenaria. Due to high growth plasticity, efficient resource allocation and tolerance of high metal concentrations, C. arenaria is a superior competitor under these conditions and can start to dominate the dune system. Carex-dominated vegetation is species-poor. Even at the moderate N-loads in this study, foliose lichens, forbs and grasses were reduced in short grass vegetation at acid sites. Species indicating these first effects of atmospheric deposition on dry, lichen-rich, short grasslands are identified and recommendations for restoration of grass-encroached sites given.     

Testing hypotheses on the dispersal and evolutionary history of freshwater mussels (Mollusca: Bivalvia: Unionidae)

The relationship between dispersal and differentiation of the European freshwater mussel Unio pictorum (Linnaeus, 1758) was studied with molecular genetic methods. Forty‐two populations from France, Italy and central Europe were analysed. Genetic relationships were assessed from the geographical distribution of allele frequencies at 17 enzyme loci. Neighbouring groups of populations show small to moderate mean genetic distances (0.020 < D_mean < 0.263). With a few exceptions the genetic affinities of the populations are the closest within the same drainage basin. In central Europe and Northern Italy genetic differences between drainage systems are relatively large. Populations from north‐eastern Italy are genetically similar to Danubian populations. Mussels from the islands of Corsica and Sardinia are more closely related to populations from the Italian peninsula than to French populations from the Rhône drainage system. Genetic relationships within U. pictorum from central Europe reflect palaeogeographical relationships between river systems during the Pliocene and Pleistocene. Literature data on two North American unionid species and one European fish species show the same relationship between genetic diversity and the history of drainage systems, although the correlations are less strong. In France and Italy this correspondence is much less evident. Population dynamic processes and human activities leading to populational bottlenecks might have obscured it.     

Colonization patterns and genetic structure of peripheral populations of the trumpeter finch (Bucanetes githagineus) from Northwest Africa, the Canary Islands and the Iberian Peninsula

Aim This paper has three aims: (1) to reconstruct the colonization history of two peripheral populations of the trumpeter finch (Bucanetes githagineus) presumably originating from the same source, one the result of an ancient expansion process and the other recently established and still expanding; (2) to estimate the importance of key events, such as past and current gene flow and bottlenecks, in both expansion processes and their contribution to the present population structure and genetic diversity; and (3) to find out whether two peripheral populations that established at widely differing times also differ in terms of genetic diversity. Location Northwest Africa (assumed source population), Canary Islands (long‐established peripheral) and south‐eastern Iberian Peninsula (recently established peripheral). Methods Bayesian analysis of population structure, individual assignment tests, F‐statistics, maximum likelihood migration estimates, genetic diversity indices and bottleneck tests were calculated with microsatellite data from 194 trumpeter finches from five breeding and two seasonal non‐breeding sites. Results Our data support the existence of two subpopulations (Canary Island and Ibero‐African) as the most likely population structure. Seasonal sites in the Iberian Peninsula had the highest percentage of birds assigned to other, mainly Iberian, sites. Pairwise F_ST values showed that the Canary Island localities were very similar to each other, but differed from the rest. Gene flow estimates within subpopulations were only slightly higher in the Canary Island population than in the Ibero‐African one. Gene diversity indices were similar at all localities. Canary Island sites show evidence of bottlenecks, whereas the Ibero‐African sites do not. Main conclusions Our data show that, at present, birds from the Canary Islands are genetically differentiated from those in North Africa and continental Spain. We could not unequivocally confirm the African origin of Canary populations because the contrary is also plausible. The Iberian Peninsula seems to have repeatedly received individuals from North Africa, which would have led to the relatively high genetic diversity found in these recently established localities and prevented bottlenecks. Movements of individuals towards sites outside their current range during the non‐breeding season are likely to precede the establishment of new breeding sites at the periphery of the distribution range.     

Genetic variation and migration pathways of maritime pine (Pinus pinaster Ait) in the Iberian peninsula

The genetic variability and migration pathways of Pinus pinaster after glaciation in the Iberian peninsula was studied by means of 18 loci from 12 natural populations of the species. The analysis showed the existence of three groups of populations with different levels of diversity and patterns of recolonization. The southern Iberian group displays a high level of diversity, with a stepping-stone model of variation. The presence of rare alleles in this group and their position in the phylogenetic tree suggest the existence of refugia during glaciations in this zone. The eastern Iberian group also has high levels of diversity but is clearly separate from the first group based on their genetic distances. The Atlantic group displays a low level of diversity that could be interpreted as a rapid recolonization of the entire area by the Eastern group that has not yet developed to a divergence in this area. The southern Iberian range is indicated to be the dispersal centre of the species after the last glaciation. Received: 15 February 1999 / Accepted: 30 April 1999     

Temporal shifts of DNA‐microsatellite allele profiles in roe deer (Capreolus capreolus L.) within three decades

DNA‐microsatellite polymorphism (four loci) was studied in 56 male roe deer (Capreolus capreolus) from a 900‐ha hunting territory in the Vosges du Nord Mountains (France), culled over 34 years (1956–1990). Changed allele frequencies at two loci within this period, and increased allelic diversity, were traced to a phase of reduced population density and subsequent immigration. Decadic population samples collected within 900‐ha were distinguished by higher genetic variability measures than were certain geographical samples across Central Europe (4–900 km). On average, the decadic cohorts were distinguished by a gene diversity index of G_ST = 0.0286, and a genetic distance of D = 0.0938, which reflect 54% (G_ST) and 69% (D) of the respective geographic (350 km) differentiation indices of roe deer in Central Europe. The importance of demography and population ecology effects for microevolution in a large mammal is demonstrated, as is the risk of artefact by composing population samples of deer over several years. Population genetic screening should cover various demes of roe deer from the same general region, and be based on many unlinked polymorphic loci, to minimize the distorting effects of genetic dynamics at the small spatial scale.     

Clonal and genetic diversity of Carex moorcroftii on the Qinghai-Tibet plateau

Carex moorcroftii Falc. ex Boott is a rhizomatous clonal sedge dominating vast alpine steppe and meadow vegetations in the hinterland of the Qinghai-Tibet plateau. To reveal the genetic and clonal structure of this species, nine populations were investigated using ten inter-simple sequence repeat (ISSR) markers. As compared to other rhizomatous Carex species, C. moorcroftii had lower genetic diversity (H_s = 0.10) at population level and higher genetic differentiation (G_st = 0.66) and lower gene flow (N_m = 0.26) between populations. Clonal diversity in C. moorcroftii in terms of Simpson index (D = 0.65) was comparable to that in other clonal species while lower than that in Carex species from the arctic and subarctic areas. The ratio of clonal diversity to genetic variation in C. moorcroftii was closely correlated with latitude, enabling a speculation about the northern migration of this species on this plateau.     

Genetic diversity of Typha latifolia (Typhaceae) and the impact of pollutants examined with tandem-repetitive DNA probes

Genetic diversity at variable-number-tandem-repeat (VNTR) loci was examined in the common cattail, Typha latifolia (Typhaceae), using three synthetic DNA probes composed of tandemly repeated “core” sequences (GACA, GATA, and GCAC). The principal objectives of this investigation were to determine whether: (1) the previously reported almost complete lack of polymorphism at allozyme loci in this species was indicative of a reduced amount of genetic diversity at VNTR loci as well; (2) VNTR markers were informative about possible clonal propagation; and (3) significant differences in genetic structure of sampling sites were associated with differences in environmental levels of pollutants at those sites. Previously, widespread sampling across the eastern United States, surveying across ten allozyme loci, has detected only two genotypes, involving a difference at a single locus, among 104 populations. In this study, the amount of genetic diversity detected at VNTR loci: (1) among ramets (N = 40; 40 genotypes detected) collected at ∼8-km intervals along a 320-km transect; (2) among ramets (N = 220; 117 genotypes detected) from five study sites separated by 50–3000 m; and (3) even among ramets within each study site [N = 44 per site; from 13 to 34 genotypes detected per site (270 m²)] exceeds that previously found in those more geographically widespread allozyme surveys. Among the 260 ramets analyzed here, the mean number of bands scored per individual was 48.61 (SD = 2.80). Mean genetic similarity among ramets collected along the 320-km transect was 0.91, which was within the range of mean genetic similarity within the five study sites (range: 0.89–0.95). Among the five study sites, 61% of the samples analyzed appeared to be clonal ramets, with up to 12 clones detected for 44 ramets sampled within a site. Clones grew intermingled and ranged up to 39 m in extent. Permutation tests of genetic similarity revealed significant genetic differentiation between each of the five study sites. Consistent with the previous allozyme studies, T. latifolia was characterized by extremely low genetic variation relative to levels of polymorphism detected at VNTR loci in other plant species. Estimated heterozygosity among ramets along the 320-km transect ranged from 0.11 to 0.13, while that within the five study sites ranged from 0.05 to 0.12. Estimates of F_st (0.32–0.41) also indicated considerable genetic subdivision among these stands. Significantly higher genetic diversity was detected at the two study sites that chemistry and toxicity data indicate to be the most severely impacted by pollutants. Although this correlation does not establish cause and effect, the results of this study indicate that the analysis of genetic diversity at VNTR loci may be a useful tool for monitoring anthropogenic-induced changes in the genetic structure of natural populations of plants.     

Role of domestication in shaping <Emphasis Type="Italic">Castanea sativa</Emphasis> genetic variation in Europe

The genetic structure of sweet chestnut (Castanea sativa Mill.) across Europe was assessed using 73 inter-simple sequence repeat markers to screen 1,768 individuals from 68 stands distributed across 29 sites in five European countries (Italy, France, Spain, Greece, and UK). At each site, trees were sampled from three distinct management types (domestication levels): naturalized stands, managed coppice, and grafted fruit orchards. In more than a third of the orchards, nonlocal genetic material (grafted clones) were evident, showing (as predicted) large differences from the other two domestication levels for most of the within-population genetic diversity parameters estimated. Randomly generated linkage disequilibrium analysis revealed weak though significant differences in two-locus allelic correlations between naturalized stands and coppice, suggesting that long-term management techniques may influence the genetic makeup of the populations. Multivariate analysis revealed the existence of five distinct gene pools across the study area; three were located in Greece, one on the northwestern coast of the Iberian peninsula and a large gene pool covering the rest of the Mediterranean basin. The implications of the results are discussed in relation to developing conservation strategies for chestnut genetic resources in Europe.     

Genetic variation and population structure ofCarex breviculmis (Cyperaceae) in Korea

We determined the genetic diversity and population structures ofCarex breviculmis (Cyperaceae) populations in Korea, using genetic variations at 23 allozyme loci.C. breviculmis is a long-lived herbaceous species that is widely distributed in eastern Asia. A high level of genetic variation was found in 15 populations. Twelve enzymes revealed 23 loci, of which 11 were polymorphic (47.8%). Genetic diversity at the speciesand population levels were 0.174 and 0.146, respectively. Total genetic diversity (H_T = 0.363) and within-population genetic diversity (H_s = 0.346) were high, whereas the extent of the population divergence was relatively low (G_ST = 0.063). Deviation from random mating (Fis) within the 15 populations was 0.206. An indirect estimate of the number of migrants per generation(Nm = 3.69) indicated that gene flow was extensive among Korean populations of this species. Analysis of fixation indices revealed a substantial heterozygote deficiency in some populations and at some loci. Genetic identity between popu-lations was high, exceeding 0.956.     

Balearic insular isolation and large continental spread framed the phylogeography of the western Mediterranean Cheirolophus intybaceus s.l. (Asteraceae)

Recent Quaternary geological and climate events have shaped the evolutionary histories of plant species in the Mediterranean basin, one of the most important hotspots of biodiversity. Genetic analyses of the western Mediterranean Cheirolophus intybaceus s.l. (Asteraceae) based on AFLP were conducted to establish the relationships between its close species and populations, to reconstruct the phylogeography of the group and to analyse potential unidirectional versus bidirectional dispersals between the Ibero‐Provençal belt and the Balearic Islands. AFLP data revealed two main genetic groups, one constituted by the Balearic populations and Garraf (NE Iberia) and the other formed by the remaining mainland populations that were further sub‐structured into two geographically separated subgroups (SE + E Iberia and NE Iberia + SW France). Genetic diversity and spatial structure analyses suggested a mid‐Pleistocene scenario for the origin of C. intybaceus in southern Iberia, followed by dispersal to the north and a single colonisation event of the Balearic archipelago from the near Dianic NE Iberian area. This hypothesis was supported by paleogeographic data, which showed the existence of terrestrial connections between the continent and the islands during the Middle–Late Pleistocene marine regressions, whereas the more recent single back‐colonisation of the mainland from Mallorca might be explained by several hypotheses, such as long‐distance dispersal mediated by migratory marine birds or sea currents.     

The molecular population structure of the tall forb Cicerbita alpina (Asteraceae) supports the idea of cryptic glacial refugia in central Europe

There is an ongoing debate about the glacial history of non‐arctic species in central and northern Europe. The two main hypotheses are: (1) postglacial colonization from refugia outside this region; (2) glacial survival in microclimatically favourable sites within the periglacial areas. In order to clarify the glacial history of a boreo‐montane tall forb, we analysed AFLPs from populations of Cicerbita alpina through most of its range (Scandinavia, the mountains of central Europe, the Alps, the Pyrenees and the Balkan Peninsula). We found a major differentiation between the Pyrenean population and all others, supported by principal coordinate, neighbour joining and STRUCTURE analyses. Furthermore, three populations from the central and north‐eastern Alps were genetically distinct from the bulk of populations from Scandinavia, central Europe, the Alps and the Balkan Peninsula. Most populations, including those from central and northern Europe, had moderate to high levels of genetic diversity (mean Shannon index H_Sh = 0.292, mean percentage of polymorphic loci P = 54.1%, mean Nei's gene diversity H = 0.195). The results indicate separate glacial refugia in the Pyrenean region and the Italian Alps. Furthermore, they provide evidence of glacial persistence in cryptic refugia north of the Alps, from where Scandinavia and most of the Alps are likely to have been colonized following deglaciation. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 142–154.     

Two colonisation stages generate two different patterns of genetic diversity within native and invasive ranges of Ulex europaeus

Genetic diversity and the way a species is introduced influence the capacity of populations of invasive species to persist in, and adapt to, their new environment. The diversity of introduced populations affects their evolutionary potential, which is particularly important for species that have invaded a wide range of habitats and climates, such as European gorse, Ulex europaeus. This species originated in the Iberian peninsula and colonised Europe in the Neolithic; over the course of the past two centuries it was introduced to, and has become invasive in, other continents. We characterised neutral genetic diversity and its structure in the native range and in invaded regions. By coupling these results with historical data, we have identified the way in which gorse populations were introduced and the consequences of introduction history on genetic diversity. Our study is based on the genotyping of individuals from 18 populations at six microsatellite loci. As U. europaeus is an allohexaploid species, we used recently developed tools that take into account genotypic ambiguity. Our results show that genetic diversity in gorse is very high and mainly contained within populations. We confirm that colonisation occurred in two stages. During the first stage, gorse spread out naturally from Spain towards northern Europe, losing some genetic diversity. During the second stage, gorse was introduced by humans into different regions of the world, from northern Europe. These introductions resulted in the loss of rare alleles but did not significantly reduce genetic diversity and thus the evolutionary potential of this invasive species.     

Modeling climate impact on an emerging disease,the Phytophthora alni‐induced alder decline

Alder decline caused by Phytophthora alni is one of the most important emerging diseases in natural ecosystems in Europe, where it has threatened riparian ecosystems for the past 20 years. Environmental factors, such as mean site temperature and soil characteristics, play an important role in the occurrence of the disease. The objective of the present work was to model and forecast the effect of environment on the severity of alder Phytophthora outbreaks, and to determine whether recent climate change might explain the disease emergence. Two alder sites networks in NE and SW France were surveyed to assess the crown health of trees; the oomycete soil inoculum was also monitored in the NE network. The main factors explaining the temporal annual variation in alder crown decline or crown recovery were the mean previous winter and previous summer temperatures. Both low winter temperatures and high summer temperatures were unfavorable to the disease. Cold winters promoted tree recovery because of poor survival of the pathogen, while hot summer temperature limited the incidence of tree decline. An SIS model explaining the dynamics of the P. alni‐induced alder decline was developed using the data of the NE site network and validated using the SW site network. This model was then used to simulate the frequency of declining alder over time with historical climate data. The last 40 years' weather conditions have been generally favorable to the establishment of the disease, indicating that others factors may be implicated in its emergence. The model, however, showed that the climate of SW France was much more favorable for the disease than that of the Northeast, because it seldom limited the overwintering of the pathogen. Depending on the European area, climate change could either enhance or decrease the severity of the alder decline.     

Field of Dreams: Restitution of Pollinator Services in Restored Bird‐Pollinated Plant Populations

Ecosystem functionality is an increasingly important objective of ecological restoration. Despite this, a few studies have rigorously assessed reproductive functionality within restored plant populations, and it is largely assumed that pollinators follow restoration of plant communities—“build it and they will come.” Here, we applied an ecological genetic approach to determine the impact of spatial separation on mating in Banksia menziesii (Proteaceae), a dominant bird‐pollinated species of Banksia woodlands of Western Australia. All plants at three post‐mining restored sites (n = 72 [13 years old], n = 21 [8 years old], and n = 20 [9 years old]), as well as a sample from an adjacent natural reference site (n = 42), were genotyped at nine microsatellite loci. Seed set, mating system parameters, realized pollen dispersal through the assignment of paternity to seed, and avian pollinator species composition, abundance and behavior, were assessed. All patches displayed equivalent heterozygosity (H_e = 0.53–0.59) and very weak genetic divergence (F_ST ≤ 0.01). Seed of plants within restored sites showed complete outcrossing and relatively high seed set, 26% of which were sired by pollen donors located beyond the local patch. Similar abundance and movement of nectar‐feeding birds was observed in restored and natural sites, despite lower bird species diversity in the restored site, where a smaller, less aggressive species was dominant. Our results demonstrate the restitution of wide outcrossing in these restored Banksia patches within an active mine‐site, and suggest that restored bird‐pollinated Banksia populations are resilient to human impacts, due largely to their generalist pollinator requirements and highly‐mobile avian pollinators.     

Colonization of the root zone ofAmmophila arenaria by harmful soil organisms

The role of harmful soil organisms in the degeneration ofAmmophila arenaria at coastal foredunes was examined by the growing of seedlings ofA. arenaria in soil samples collected from its root zone. Three sites, each representing a successive stage in foredune succession were examined: (1) a highly mobile dune (sand accretion of 80 cm year⁻¹) with vigorousA. arenaria, colonizing only the upper 30-cm of the annually deposited layer of sand, (2) a mobile dune with vigorousA. arenaria (sand accretion of 22 cm year⁻¹) and a 1-metre soil profile completely colonized by roots and (3) a stable dune (no sand accretion) with degeneratedA. arenaria and young roots mainly present in the upper 0–10 cm. In the upper part of the highly mobile site, the presence of harmful soil organisms was confined to the root layers and at the mobile site for all depth layers a significant growth reduction ofA. arenaria was observed due to the activity of harmful soil organisms. At the stable site, however, growth had only been reduced in some of the depth layers. At all sites newly formed roots ofA. arenaria had been colonized by harmful soil organisms within one year. If present in sand prior to root growth harmful soil organisms reduced root length and root hair formation severely and they enhanced branching of the roots. It is concluded that harmful soil organisms initiate degeneration ofA. arenaria in stable dunes by attack of the root system, which makes the plants suffer from abiotic stress.     

Population genomics of rapidly invading lionfish in the Caribbean reveals signals of range expansion in the absence of spatial population structure

Range expansions driven by global change and species invasions may have significant genomic, evolutionary, and ecological implications. During range expansions, strong genetic drift characterized by repeated founder events can result in decreased genetic diversity with increased distance from the center of the historic range, or the point of invasion. The invasion of the Indo‐Pacific lionfish, Pterois volitans, into waters off the US East Coast, Gulf of Mexico, and Caribbean Sea provides a natural system to study rapid range expansion in an invasive marine fish with high dispersal capabilities. We report results from 12,759 single nucleotide polymorphism loci sequenced by restriction enzyme‐associated DNA sequencing for nine P. volitans sampling areas in the invaded range, including Florida and other sites throughout the Caribbean, as well as mitochondrial control region D‐loop data. Analyses revealed low to no spatially explicit metapopulation genetic structure, which is partly consistent with previous finding of little structure within ocean basins, but partly divergent from initial reports of between‐basin structure. Genetic diversity, however, was not homogeneous across all sampled sites. Patterns of genetic diversity correlate with invasion pathway. Observed heterozygosity, averaged across all loci within a population, decreases with distance from Florida while expected heterozygosity is mostly constant in sampled populations, indicating population genetic disequilibrium correlated with distance from the point of invasion. Using an F_ST outlier analysis and a Bayesian environmental correlation analysis, we identified 256 and 616 loci, respectively, that could be experiencing selection or genetic drift. Of these, 24 loci were shared between the two methods.