The genetic structure of raccoon introduced in Central Europe reflects multiple invasion pathways

Invasions of non-native species are of great concern as they have a devastating impact on native biodiversity and can also affect the economy of a region. Multiple introductions in several locations of a new range greatly promote the success of non-native species. The raccoon (Procyon lotor) is an omnivore whose native distribution extends from southern Canada to Panama. It has been successfully introduced in many European countries. We examined the microsatellite and mitochondrial diversity of raccoon populations in Central Europe (Germany, Poland, and Czech Republic) in order to determine their introduction sources and pathways as well as the factors affecting genetic structure in this invasive species. We found low diversity of the mtDNA control region and moderate diversity of microsatellite markers. Raccoon showed three hierarchic levels of genetic structure which separate at different levels sampled from Czech Republic, Germany and raccoon inhabiting two different habitats in Poland. In Poland the raccoon population was established through migration from Germany to Czech Republic. Analysis of the intensity of migration between two different habitat types indicated source-sink dynamics in the Polish populations of raccoons. Our results confirm the high intensity of the raccoon invasion in Central Europe and point to specific measures needed as part of an effective management strategy.     

Strong population genetic structure of an invasive species,Rhynchophorus ferrugineus (Olivier), in southern China

The red palm weevil (RPW), Rhynchophorus ferrugineus (Olivier), was initially reported in China in the 1990s and is now considered one of the most successful invasive pests of palm plants in the country. A total of 14 microsatellite loci and one mitochondrial cytochrome oxidase subunit Ι (cox I) gene fragment were used to investigate the genetic characteristics and structure of R. ferrugineus in southern China. High levels of genetic differentiation among populations and significant correlations between genetic and geographical distances indicated an important role of geographical distance in the distribution of the RPW in southern China. High gene flow between Fujian and Taiwan province populations illustrated the increased effects of frequent anthropogenic activities on gene flow between them. Genetic similarity (i.e., haplotype similarity) indicated that RPW individuals from Taiwan and Fujian invaded from a different source than those from Hainan. To some extent, the genetic structure of the RPW in southern China correlated well with the geographic origins of this pest. We propose that geographical distance, anthropogenic activities, and the biological attributes of this pest are responsible for the distribution pattern of the RPW in southern China. The phylogenetic analysis suggests that the most likely native sources of the RPW in southern China are India, the Philippines, and Vietnam.     

Fine-scale genetic structure arises during range expansion of an invasive gecko

Processes of range expansion are increasingly important in light of current concerns about invasive species and range shifts due to climate change. Theoretical studies suggest that genetic structuring may occur during range expansion. Ephemeral genetic structure can have important evolutionary implications, such as propagating genetic changes along the wave front of expansion, yet few studies have shown evidence of such structure. We tested the hypothesis that genetic structure arises during range expansion in Hemidactylus mabouia, a nocturnal African gecko recently introduced to Florida, USA. Twelve highly variable microsatellite loci were used to screen 418 individuals collected from 43 locations from four sampling sites across Florida, representing a gradient from earlier (～1990s) to very recent colonization. We found earlier colonized locations had little detectable genetic structure and higher allelic richness than more recently colonized locations. Genetic structuring was pronounced among locations at spatial scales of tens to hundreds of meters near the leading edge of range expansion. Despite the rapid pace of range expansion in this introduced gecko, dispersal is limited among many suitable habitat patches. Fine-scale genetic structure is likely the result of founder effects during colonization of suitable habitat patches. It may be obscured over time and by scale-dependent modes of dispersal. Further studies are needed to determine if such genetic structure affects adaptation and trait evolution in range expansions and range shifts.     

Host‐mediated shift in the cold tolerance of an invasive insect

While many insects cannot survive the formation of ice within their bodies, a few species can. On the evolutionary continuum from freeze‐intolerant (i.e., freeze‐avoidant) to freeze‐tolerant insects, intermediates likely exist that can withstand some ice formation, but not enough to be considered fully freeze tolerant. Theory suggests that freeze tolerance should be favored over freeze avoidance among individuals that have low relative fitness before exposure to cold. For phytophagous insects, numerous studies have shown that host (or nutrition) can affect fitness and cold‐tolerance strategy, respectively, but no research has investigated whether changes in fitness caused by different hosts of polyphagous species could lead to systematic changes in cold‐tolerance strategy. We tested this relationship with the invasive, polyphagous moth, Epiphyas postvittana (Walker). Host affected components of fitness, such as larval survivorship rates, pupal mass, and immature developmental times. Host species also caused a dramatic change in survival of late‐instar larvae after the onset of freezing—from less than 8% to nearly 80%. The degree of survival after the onset of freezing was inversely correlated with components of fitness in the absence of cold exposure. Our research is the first empirical evidence of an evolutionary mechanism that may drive changes in cold‐tolerance strategies. Additionally, characterizing the effects of host plants on insect cold tolerance will enhance forecasts of invasive species dynamics, especially under climate change.     

Long-term population genetic structure of an invasive urochordate: the ascidian Botryllus schlosseri

The accelerated pace of marine biological invasions raises questions pertaining to genetic traits and dynamics underlying the successful establishment of invasive species. Current research stresses the importance of multiple introductions and prolonged gene flow as the main sources for genetic diversity, which, along with genetic drift, affect invasive species success. We here attempt to determine the relative contribution of gene flow and mutation rates as sources of genetic variability using the invasive tunicate Botryllus schlosseri as a model. The study was performed over a 13-year period in the Santa Cruz Harbor, California. With a characteristic life history of five generations/year, the Santa Cruz Botryllus population has already experienced approximately 155 generations since the onset of its invasion. The results (278 specimens, 127 scored alleles, five microsatellite loci) support limited gene flow rate (2.89?×?10^?3) and relative genetic isolation. Furthermore, the study population was found to be influenced by both, genetic drift and a high mutation rate (2.47?×?10^?2). These findings were supported by high fluctuations in the frequencies of microsatellite alleles, the appearance of new alleles and the loss of others. The balance between genetic drift and a high mutation rate is further elucidated by the high, stable level of genetic variation. We suggest that rapid mutation rates at the microsatellite loci reflect genome-wide phenomena, helping to maintain high genetic variability in relatively isolated populations. The potential adaptability to new environments is discussed.     

Modelling the impact of an invasive insect via reaction-diffusion

An exotic, specialist seed chalcid, Megastigmus schimitscheki, has been introduced along with its cedar host seeds from Turkey to southeastern France during the early 1990s. It is now expanding in plantations of Atlas Cedar (Cedrus atlantica). We propose a model to predict the expansion and impact of this insect. This model couples a time-discrete equation for the ovo-larval stage with a two-dimensional reaction-diffusion equation for the adult stage, through a formula linking the solution of the reaction-diffusion equation to a seed attack rate. Two main diffusion operators, of Fokker-Planck and Fickian types, are tested. We show that taking account of the dependence of the insect mobility with respect to spatial heterogeneity, and choosing the appropriate diffusion operator, are critical factors for obtaining good predictions.     

Phylogeography of a host-specific insect: genetic structure of Ips typographus in Europe does not reflect past fragmentation of its host

The phylogeography of the bark beetle Ips typographus was assessed using five microsatellite markers. Twenty-eight populations were sampled throughout Europe on the host tree Picea abies . I. typographus showed very low levels of genetic diversity, and the study revealed a lack of genetic structure across Europe. No significant barrier to gene flow was found, even though P. abies has a fragmented distribution. A weak but significant effect of isolation by distance was found. These results suggest a high dispersal capacity of I. typographus , which leads to low genetic differentiation between populations. Its high dispersal capacity is likely to have prevented I. typographus from developing important local adaptations to its host, which would have influenced its genetic structure. The nuclear data was compared to previously published mitochondrial data that showed strong differentiation between Central–Northern European populations and Russian–Baltic populations, and a founder effect in Scandinavia, probably reflecting the postglacial history of I. typographus . Discrepancies between nuclear and mitochondrial markers could be due to the maternal inheritance of mitochondrial DNA, and to sex-biased dispersal in I. typographus . The overall low genetic diversity observed on both markers on a large geographical scale is discussed. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 239–246.     

Invasive species of Heracleum in Europe: an insight into genetic relationships and invasion history

Several species of the genus Heracleum (Umbelliferae) were introduced into Europe from south-west Asia in the 19th century and are now widespread in many countries. At least three invasive taxa with unresolved relationships to one another are thought to occur in Europe: Heracleum mantegazzianum Sommier & Levier, H. sosnowskyi Manden, and H. persicum Desf. ex Fischer. They are tall plants forming extensive stands with a high cover. To elucidate genetic relationships between the species, and gain insight into their invasion history, samples were collected from native ranges in Asia and invaded ranges of the three species in Europe and analysed using amplified fragment length polymorphism. Five other Heracleum species were also studied and in total, 189 samples from 72 populations were analysed. The results confirmed that there are three distinct tall Heracleum species invading in Europe. Within each of the three species, plants collected in the invaded range are genetically close to those from their native ranges. A close genetic relationship between the three invasive Heracleum species in Europe was also found. A high overall genetic variability detected in the invaded range suggests that the majority of invading populations were not affected by a genetic bottleneck and that rapid evolution, drift, or hybridization played a role in genetic structuring of invading populations. For H. mantegazzianum , genetic distance of populations in the native range significantly decreased with geographical distance, but not in the invaded range. It is likely that the current pattern of genetic diversity in Europe resulted from multiple introductions of all three species.     

Multiple processes drive genetic structure of humpback whale (Megaptera novaeangliae) populations across spatial scales

Elucidating patterns of population structure for species with complex life histories, and disentangling the processes driving such patterns, remains a significant analytical challenge. Humpback whale (Megaptera novaeangliae) populations display complex genetic structures that have not been fully resolved at all spatial scales. We generated a data set of nuclear markers for 3575 samples spanning the seven breeding stocks and substocks found in the South Atlantic and western and northern Indian Oceans. For the total sample, and males and females separately, we assessed genetic diversity, tested for genetic differentiation between putative populations and isolation by distance, estimated the number of genetic clusters without a priori population information and estimated rates of gene flow using maximum‐likelihood and Bayesian approaches. At the ocean basin scale, structure is governed by geographical distance (IBD P < 0.05) and female fidelity to breeding areas, in line with current understanding of the drivers of broadscale population structure. Consistent with previous studies, the Arabian Sea breeding stock was highly genetically differentiated (F_ST 0.034–0.161; P < 0.01 for all comparisons). However, the breeding stock boundary between west South Africa and east Africa was more porous than expected based on genetic differentiation, cluster and geneflow analyses. Instances of male fidelity to breeding areas and relatively high rates of dispersal for females were also observed between the three substocks in the western Indian Ocean. The relationships between demographic units and current management boundaries may have ramifications for assessments of the status and continued protections of populations still in recovery from commercial whaling.     

Fine‐scale spatial genetic structure of common and declining bumble bees across an agricultural landscape

Land‐use changes have threatened populations of many insect pollinators, including bumble bees. Patterns of dispersal and gene flow are key determinants of species' ability to respond to land‐use change, but have been little investigated at a fine scale (<10 km) in bumble bees. Using microsatellite markers, we determined the fine‐scale spatial genetic structure of populations of four common Bombus species (B. terrestris, B. lapidarius, B. pascuorum and B. hortorum) and one declining species (B. ruderatus) in an agricultural landscape in Southern England, UK. The study landscape contained sown flower patches representing agri‐environment options for pollinators. We found that, as expected, the B. ruderatus population was characterized by relatively low heterozygosity, number of alleles and colony density. Across all species, inbreeding was absent or present but weak (F_IS = 0.01–0.02). Using queen genotypes reconstructed from worker sibships and colony locations estimated from the positions of workers within these sibships, we found that significant isolation by distance was absent in B. lapidarius, B. hortorum and B. ruderatus. In B. terrestris and B. pascuorum, it was present but weak; for example, in these two species, expected relatedness of queens founding colonies 1 m apart was 0.02. These results show that bumble bee populations exhibit low levels of spatial genetic structure at fine spatial scales, most likely because of ongoing gene flow via widespread queen dispersal. In addition, the results demonstrate the potential for agri‐environment scheme conservation measures to facilitate fine‐scale gene flow by creating a more even distribution of suitable habitats across landscapes.     

Population genetic structure across dissolved oxygen regimes in an African cichlid fish

Ecological isolation is a process whereby gene flow between selective environments is reduced due to selection against maladapted dispersers, migrant alleles, or hybrids. Although ecological isolation has been documented in several systems, gene flow can often be high among selective regimes, and more studies are thus needed to better understand the conditions under which ecological gradients or divergent selective regimes should influence population structure. We test for ecological isolation in a system in which high plasticity occurs with respect to traits that are adaptive in alternate forms under different environmental conditions. Pseudocrenilabrus multicolor victoriae is a widespread haplochromine cichlid fish in East Africa that exploits both normoxic (normal oxygen) rivers/lakes and hypoxic (low oxygen) swamps. Here, we examine population structure, using mitochondrial DNA and microsatellites, to determine if genetic divergence is significantly increased between dissolved oxygen regimes relative to within them, while controlling for geographical structure. Our results indicate that geographical separation influences population structure, while no effects of divergent selection with respect to oxygen regimes were detected. Specifically, we document (i) genetic clustering according to geographical region, but no clustering according to oxygen regime; (ii) higher genetic variation among than within regions, but no effect of oxygen regime on genetic variation; (iii) isolation by distance within one region; and (iv) decreasing genetic variability with increasing geographical distance from Lake Victoria. We speculate that plasticity may be facilitating gene flow between oxygen regimes in this system.     

Scaling of processes shaping the clonal dynamics and genetic mosaic of seagrasses through temporal genetic monitoring

Theoretically, the dynamics of clonal and genetic diversities of clonal plant populations are strongly influenced by the competition among clones and rate of seedling recruitment, but little empirical assessment has been made of such dynamics through temporal genetic surveys. We aimed to quantify 3 years of evolution in the clonal and genetic composition of Zostera marina meadows, comparing parameters describing clonal architecture and genetic diversity at nine microsatellite markers. Variations in clonal structure revealed a decrease in the evenness of ramet distribution among genets. This illustrates the increasing dominance of some clonal lineages (multilocus lineages, MLLs) in populations. Despite the persistence of these MLLs over time, genetic differentiation was much stronger in time than in space, at the local scale. Contrastingly with the short-term evolution of clonal architecture, the patterns of genetic structure and genetic diversity sensu stricto (that is, heterozygosity and allelic richness) were stable in time. These results suggest the coexistence of (i) a fine grained (at the scale of a 20 × 30 m quadrat) stable core of persistent genets originating from an initial seedling recruitment and developing spatial dominance through clonal elongation; and (ii) a local (at the scale of the meadow) pool of transient genets subjected to annual turnover. This simultaneous occurrence of initial and repeated recruitment strategies highlights the different spatial scales at which distinct evolutionary drivers and mating systems (clonal competition, clonal growth, propagule dispersal and so on) operate to shape the dynamics of populations and the evolution of polymorphism in space and time.     

Contrasting patterns of genetic diversity and spatial structure in an invasive symbiont-host association

Do host invaders and their associated symbiont co-invaders have different genetic responses to the same invasion process? To answer this question, we compared genetic patterns of native and exotic populations of an invasive symbiont-host association. This is an approach applied by very few studies, of which most are based on parasites with complex life cycles. We used the mitochondrial genetic marker cytochrome oxidase subunit I (COI) to investigate a non-parasitic freshwater ectosymbiont with direct life-cycle, low host specificity and well-documented invasion history. The study system was the crayfish Procambarus clarkii and its commensal ostracod Ankylocythere sinuosa, sampled in native (N American) and exotic (European) ranges. Results of analyses indicated: (1) higher genetic diversity in the symbiont than its host; (2) genetic diversity loss in the exotic range for both species, but less pronounced in the symbiont; (3) native populations genetically structured in space, with stronger patterns in the symbiont and (4) loss of spatial genetic structure in the exotic range in both species. The combination of historical, demographic and genetic data supports a higher genetic diversity of source populations and a higher propagule size that allowed the symbiont to overcome founder effects better than its host co-invader. Thus, the symbiont might be endowed with a higher adaptive potential to new hosts or off-host environmental pressures expected in the invasive range. We highlight the usefulness of this relatively unexplored kind of symbiont-host systems in the invasion context to test important ecological and evolutionary questions.     

Understanding invasion history: genetic structure and diversity of two globally invasive plants and implications for their management

Aim Resolving the origin of invasive plant species is important for understanding the introduction histories of successful invaders and aiding strategies aimed at their management. This study aimed to infer the number and origin(s) of introduction for the globally invasive species, Macfadyena unguis‐cati and Jatropha gossypiifolia using molecular data. Location Native range: Neotropics; Invaded range: North America, Africa, Europe, Asia, Pacific Islands and Australia. Methods We used chloroplast microsatellites (cpSSRs) to elucidate the origin(s) of introduced populations and calculated the genetic diversity in native and introduced regions. Results Strong genetic structure was found within the native range of M. unguis‐cati, but no genetic structuring was evident in the native range of J. gossypiifolia. Overall, 27 haplotypes were found in the native range of M. unguis‐cati. Only four haplotypes were found in the introduced range, with more than 96% of introduced specimens matching a haplotype from Paraguay. In contrast, 15 haplotypes were found in the introduced range of J. gossypiifolia, with all invasive populations, except New Caledonia, comprising multiple haplotypes. Main conclusions These data show that two invasive plant species from the same native range have had vastly different introduction histories in their non‐native ranges. Invasive populations of M. unguis‐cati probably came from a single or few independent introductions, whereas most invasive J. gossypiifolia populations arose from multiple introductions or alternatively from a representative sample of genetic diversity from a panmictic native range. As introduced M. unguis‐cati populations are dominated by a single haplotype, locally adapted natural enemies should make the best control agents. However, invasive populations of J. gossypiifolia are genetically diverse and the selection of bio‐control agents will be considerably more complex.     

Population genetic structure of Arabidopsis lyrata in Europe

Population genetic theory predicts that the self-incompatible and perennial herb, Arabidopsis lyrata, will have a genetic structure that differs from the self-fertilizing, annual Arabidopsis thaliana. We quantified the genetic structure for eight populations of A. lyrata ssp. petraea in historically nonglaciated regions of central Europe. Analysis of 20 microsatellite loci for 344 individuals demonstrated that, in accordance with predictions, diploid populations had high genome-wide heterozygosity (H(O) = 0.48; H(E) = 0.52), high within-population diversity (83% of total) compatible with mutation-drift equilibrium, and moderate differentiation among populations (F(ST) = 0.17). Within a single population, the vast majority of genetic variability (92%) was found at the smallest spatial scale (< 3 m). Although there was no evidence of biparental inbreeding or clonal propagation at this scale (F(IS) = 0.003), significant fine-scale spatial autocorrelation indicated localized gene flow presumably due to gravity dispersed seeds (Sp = 0.018). Limited gene flow between isolated population clusters (regions) separated by hundreds of kilometres has given rise to an isolation by distance pattern of diversification, with low, but significant, differentiation among regions (F(ST) = 0.05). The maintenance of geographically widespread polymorphisms and uniformly high diversity throughout central Europe is consistent with periglacial survival of A. lyrata ssp. petraea north of the Alps in steppe-tundra habitats during the last glacial maximum. As expected of northern and previously glaciated localities, A. lyrata in Iceland was genetically less diverse and highly differentiated from central Europe (H(E) = 0.37; F(ST) = 0.27).     

The structure of an insect chymotrypsin

The South American imported fire ant (Solenopsis invicta), without natural enemies in the United States, widely infests the southern United States, causing more than a half billion dollars in health and agriculture-related damage annually in Texas alone. Fire ants are resistant to most insecticides, so control will require a more fundamental understanding of their biochemistry and metabolism leading to the design of selective, ecologically safe insecticides. The 4th instar larvae play a crucial role in the nutrition of the colony by secreting proteinases (especially chymotrypsin) which digest food products for the entire colony. The first structure of an ant proteolytic enzyme, fire ant chymotrypsin, was determined to atomic resolution (1.7 A). A structural comparison of the ant and mammalian structures confirms the "universality" of the serine proteinase motif and reveals a difference at residues 147-148, which are proteolytically removed in the bovine enzyme but are firmly intact in the ant chymotrypsin, suggesting a different activation mechanism for the latter. Likewise, the absence of the covalently attached propeptide domain (1-15) further suggests an uncharacteristic activation mechanism. The presence of Gly189 in the S1 site is an atypical feature of this chymotrypsin and is comparable only to human leukocyte elastase, hornet chymotrypsin and fiddler crab collagenase. Binding studies confirm the chymotrypsin nature of this novel enzyme.     

Population genetic variation and structure of the invasive weed Mikania micrantha in southern China: consequences of rapid range expansion

Invasive plants such as Mikania micrantha provide valuable opportunities for studying population genetic consequences of rapid range expansion. Twenty-eight populations of M. micrantha throughout its introduced range in southern China were examined by using intersimple sequence repeat markers. Population genetic parameters were estimated by Bayesian approaches as well as conventional methods. Bottleneck signature, multilocus linkage disequilibrium, character compatibility, and cluster analyses were conducted to assay the factors that may act to shape population variability. High levels of genetic variation and differentiation were detected in the introduced populations of M. micrantha. All populations experienced severe bottlenecks. Most of them demonstrated significant linkage disequilibrium and matrix compatibility. Populations were mainly clustered into 2 groups, and those from different regions intermingled in the unweighted pair group method with arithmetic mean (UPGMA) dendrogram. No geographical signature was found in the pattern of population genetic variation. This research indicates that during M. micrantha invasion, multiple introductions mitigated the loss of genetic variation associated with bottlenecks. Nonetheless, bottlenecks enhanced the population differentiation. Human-mediated long-distance dispersal events of seeds or propagules explain the lack of geographic structure in genetic variation. Although asexual reproduction is the predominant mating mode in M. micrantha, it has little effect on the population genetic composition.     

Effects of vegetation structure and landscape complexity on insect parasitism across an agricultural frontier in Argentina

Insect parasitism patterns are influenced by vegetation structure and landscape complexity. Our objective was to examine the effects of vegetation structure and landscape complexity on parasitism based on direct measurements of structure and diversity indices as well as on metrics based on remote sensing using Quickbird images. We collected 2266 lepidopteran larvae and pupae, including different families and habits, to estimate parasitism, and recorded vegetation characteristics in five 100-m² transects and 18 1 ha-plots in the dry Chaco, Northwest Argentina. We calculated landscape metrics and semivariograms in the plots from the image. The plots represented four “complexity groups”: agricultural, riparian/hedgerow, bare ground, and forest plots. Mean parasitism in the study sites was 10.7% (min: 0%, max: 23%). Parasitism was highest in agricultural plots, lowest in forest plots, and intermediate in riparian/hedgerow and bare ground plots. The landscape model explained parasitism more than the vegetation model. The landscape final model included Normalized Difference Vegetation Index (NDVI) Range, a measure of landscape heterogeneity, and Mean Shape Index, a measure of patch shape irregularity, and their interaction. The vegetation model included basal area and the Coefficient of Variation of tree density among transects, a measure of tree spatial distribution within a plot. Our results agree with previous studies that found higher parasitism in agricultural vs. non-agricultural environments in the subtropics, while riparian/hedgerow plots were important for conserving parasitism, as reported for temperate environments. We showed that under-explored tools such as the semivariogram and satellite band combinations were useful for the assessment of parasitism and that studying vegetation and landscape complexity simultaneously can help us examine mechanisms in detail. The identified variables related to high parasitism should be used for image classifications with a functional approach.