Significant Loss Of Genetic Diversity Research Articles

High genetic diversity but limited gene flow in Flemish populations of the crested newt, Triturus cristatus

Habitat destruction and fragmentation are among the major causes of amphibian decline. We investigated to what extent geographic distance and barriers affect the genetic composition of the crested newt, Triturus cristatus in Flanders (North Belgium), causing inbreeding or loss of genetic diversity. Data from seven microsatellite loci and 170 individuals from seven metapopulations up to 180km apart revealed heterozygosities of 0.53 to 0.67 within populations and moderate levels of genetic divergence between populations (FST values from 0.074 to 0.141, harmonic means of Dest between 0.070 and 0.189). In all Flemish meta-populations, more than 90% of the individuals from a given geographic region were assigned to the same genetic cluster indicating
 little genetic exchange, even in De Panne where the two populations Oosthoek and Westhoek are only a few kilometres apart. Such sub-structuring on a micro-scale has also been described in other amphibians. Unique alleles in most populations further support the probability that genetic drift has already led to some isolation. With the exception of the Oosthoek population, however, we found no significant evidence for bottlenecks. Connectivity within pool clusters seems essential to the maintenance of genetic diversity in crested newts as is indicated by our findings from Tommelen, the population with the largest number of pools in close proximity, which also shows the highest levels of heterozygosity (He and Ho) and the second highest number and richness of alleles. In conclusion, our study indicates that dispersal and migration rates between the Flemish populations of Triturus cristatus are limited at the geographic scale studied here but that habitat fragmentation has not yet led to a significant loss of genetic diversity of the studied Flemish populations, possibly because crested newts are relatively long-lived, fragmentation of their habitat is relatively recent in Flanders, and most investigated pools are still connected at the local scale.

Assessing the genetic vulnerability of Macaúba palm [Acrocomia aculeata (Jacq.) Lodd. ex Mart.] through the mating system and genetic diversity of open‐pollinated progenies

AbstractAt present, intelligent and sustainable agriculture presupposes a compromise between maximising crop yield and minimising its risk of genetic vulnerability. Breeding programmes should implement strategies that allow the development of superior genotypes and preserve genetic diversity, especially in perennial plants. The Macaúba palm (Acrocomia aculeata) is a species with the potential to produce oil at a level comparable to that of the oil palm, even in water‐deficient areas, which motivates its commercial interest and drives an increase in demand for seedlings from natural populations for commercial plantations. Therefore, to evaluate the impact of this selection procedure on the reduction of genetic diversity and, consequently, the genetic vulnerability of commercial planting, in the present study we analysed the population mating system and the genetic diversity of Open‐Pollinated Progenies (OPPs) from selected seed‐trees in relation to the genetic diversity of respective native populations (NPs). To achieve this, we evaluated the mating system and genetic diversity employing 14 microsatellite markers (SSR). The mating system indices estimated for A. aculeata palm indicated that the species present a mixed mating system () with a predominance of outcrossing. However, at the population level, the outcrossing rate ranged from . The biparental inbreeding rate was considered moderate (), with some variation between populations (from 0.0005 to 0.275). The multilocus correlated paternity was , ranging from 0 to 0.112 at population level, indicating that a significant portion of the progeny consisted of half‐sibs. The results demonstrate that there was no significant loss of genetic diversity of OPPs derived from artificial selection within NPs. In the OPPs the number of alleles (Na = 2.55) was similar to that of NP (Na = 2.56). Furthermore, the mean values of observed heterozygosity (HO) between NP and OPPs were similar, with a mean of 0.366 and 0.356, respectively. In conclusion, the procedure adopted to produce commercial seedlings in the present study should not represent a high risk of genetic vulnerability. In addition, our results will provide a guidance to breeders regarding selection intensity in both natural and improved populations, aiming to optimise the advancement of generations, thereby maximising future genetic gains while preserving genetic diversity. However, we recommend verifying the outcrossing rate and genetic diversity at the population level, as these factors could have significant effects on the vulnerability of the species and the macaúba crop.

Genetic diversity in ex situ populations of the endangered Leontopithecus chrysomelas and implications for its conservation.

Leontopithecus chrysomelas, the Golden-headed Lion Tamarin (GHLT), is an endangered and endemic Neotropical primate from the Atlantic Forest of Brazil that has suffered a reduction of its habitat and population size in the wild. Ex situ populations have been established as a relevant alternative to safeguard the species and retain its genetic diversity and evolutionary potential. This study evaluated the genetic diversity and structure of the two main Brazilian captive populations of GHLT, which have been under human care at the Primatology Center of Rio de Janeiro (CPRJ) and the Zoological Park Foundation of São Paulo (FPZSP). Our results revealed levels of genetic diversity overall comparable to those observed for other Leontopithecus species and for ex situ and in situ populations of GHLT previously studied. Bayesian and principal coordinate analyses showed a moderate differentiation between CPRJ and FPZSP populations. Both populations presented observed heterozygosity values higher than expected heterozygosity values for most of the microsatellites used in this study, suggesting that the management has been efficient in avoiding an increase in homozygosity. However, simulations point to a significant loss of genetic diversity in the next 100 years, mainly in the FPZSP population. Such data are relevant for further decision-making on the metapopulation management of L. chrysomelas in captive conditions and for integrating in situ and ex situ conservation plans.

Patterns of genetic diversity: Stepping‐stone dispersal of an invasive fish introduced by an inter‐basin water transfer project

Abstract Knowledge of large‐scale dispersal processes and their associated genetic diversity patterns is significant for managing invasive species. These patterns remain unclear for invasive species that colonise new habitats through inter‐basin water transfer projects. A worm goby Taenioides cirratus colonised several large inland lakes in China, thereby expanding its distribution through the East Route of the South‐to‐North Water Transfer Project (ESNT). Here, we used nuclear microsatellites to analyse patterns of genetic diversity, population structure, gene flow and, invasion history across its native and invasive ranges in China. Our objectives were to: (a) reveal contemporary genetic diversity patterns of T. cirratus in two native and four invasive populations in China; and (b) identify its main model of dispersal in the ESNT. Invasive populations experienced significant loss of genetic diversity because of bottlenecks and low levels of gene flow, and strong population genetic structure due to founder effects that occurred during expansions. Significant genetic isolation‐by‐distance patterns were largely influenced by landscape connectivity and the reduced active dispersal ability of T. cirratus. The one‐way stepping‐stone dispersal model was identified as being most likely for T. cirratus in the ESNT, influenced by the long distance of upstream dispersal and downstream water transfer events. Our results highlight that T. cirratus could overcome low genetic diversity in founding populations, allowing for invasive spread. For management, we suggest physical removal of invasive populations and installation of deterrents near the pump intake area and the lake outflow to reduce further spread in the system. We provided a general paradigm for understanding dispersal patterns involved in inter‐basin water transfers.

Genetic Diversity of Campomanesia adamantium and Its Correlation with Land Use and Land Cover

(1) Background: Campomanesia adamantium is an endemic species of the Cerrado and this biome has been under threat by its constant degradation. The genetic diversity of C. adamantium was characterized using species-specific microsatellites in two different time periods and correlations of these parameters of genetic diversity with the land use and land cover data. (2) Methods: We used 10 microsatellite loci to analyze C. adamantium from five populations, collected in 2011 and 2017. Maps of land use and land cover of the collection sites in both years were generated and subsequently correlated with genetic diversity. (3) Results: No significant loss of genetic diversity was observed in the analyzed period and a positive inbreeding coefficient was observed in all populations. AMOVA and STRUCTURE showed that there is no population structure between years and populations. Significant Pearson correlations were observed in 2017 between parameters of genetic diversity and land use and land cover, with a positive correlation between expected heterozygosity and secondary vegetation, and a negative correlation between inbreeding coefficient and exposed soil. (4) Conclusions: There was no decline in genetic diversity from 2011 to 2017. The high rates of the inbreeding coefficient could lead, for the species, in the long run, to an inbreeding depression as the Cerrado fragmentation might cause a population bottleneck.

Significant loss of genetic diversity and accumulation of deleterious genetic variation in a critically endangered azalea species, Rhododendron boninense, growing on the Bonin Islands

AbstractLoss of genetic diversity increases the risk of extinction of a population through inbreeding depression. In addition, the number of deleterious genetic variations, which might accumulate in a small population through genetic drift, can also make the population vulnerable. Rhododendron boninense is a critically endangered azalea species, which grows on the Bonin Islands, a UNESCO World Heritage Site; its population size in the wild dropped to only a single individual. Although a governmental program for species conservation has been conducted, no successful natural regeneration or population growth was achieved. We hypothesized that the reduced genetic diversity and accumulated deleterious genetic variation might cause the vulnerability of the species, and conducted comparative genetic and genomic analyses between R. boninense and its congeners. Genetic analysis using microsatellite markers indicated that the genetic diversity of R. boninense was ultimately low; microsatellite loci of this species were all fixed, whereas the congeners maintain high allelic diversity. Based on comprehensive transcriptome analysis, the amount of deleterious variation of R. boninense was significantly greater than that of R. amanoi. Repeated generation transitions of the small population of R. boninense on the oceanic islands is likely to have resulted in low genetic diversity as well as more deleterious variations in the genome, and we speculated that the accumulated deleterious variation might result in vulnerability of R. boninense. This study indicates the possibility of evaluating the feasibility of effective conservation programs based on the genetic diversity and the amount of accumulated deleterious variation in the genome of critically endangered species.

Characterization of the Genetic Resources of Farmed Tambaqui in Northern Brazil

The present study analyzed the genetic variability and structure of farmed tambaqui in the Brazilian state of Pará, and provided basic information that can be used for the development of programs of monitoring and management of genetic resources in the aquaculture operations of northern Brazil. A total of 216 individuals were sampled from tambaqui farms in Pará. Genotyping was based on a multiplex set of 10 tri- and tetra-nucleotide microsatellite markers. The data were used to calculate genetic diversity indices, expected and observed heterozygosity, the number of alleles per locus, allelic richness, and inbreeding coefficient. Genetic structure was verified using DEST and RST, the genetic signature, and Bayesian analysis. The results showed that the tambaqui farms surveyed have suffered a significant loss of genetic variability, and that they are genetically structured, forming two clusters, one encompassing the farms in western Pará, and the other including the farms from the northeast and southeast regions of the state. These finding provide fundamental insights for the development of effective strategies that will help guarantee productivity and the quality of the tambaqui farms of northern Brazil, and provide a database for the upgrading of the genetic variability of these populations. This study indicated the need for hatcheries in southeastern and northeastern Pará to amplify or renew their breeding stocks, in order to avoid the significant loss of genetic diversity in the tambaqui farms of these regions.

SNP-based genetic characterization of the Tulane National Primate Research Center's conventional and specific pathogen-free rhesus macaque (Macaca mulatta) populations.

The rhesus macaque is an important biomedical model organism, and the Tulane National Primate Research Center (TNPRC) has one of the largest rhesus macaque breeding colonies in the United States. SNP profiles from 3266 rhesus macaques were used to examine the TNPRC colony genetic composition over time and across conventional or SPF animals of Chinese and Indian ancestry. Chinese origin animals were the least genetically diverse and the most inbred; however, since their derivation from their conventional forebearers, neither the Chinese nor the Indian SPF animals exhibit any significant loss of genetic diversity or differentiation. The TNPRC colony managers have successfully minimized loss in genetic variation across generations. Although founder effects and bottlenecks among the Indian animals have been successfully curtailed, the Chinese subpopulation still show some influences from these events.

Climatic changes can drive the loss of genetic diversity in a Neotropical savanna tree species.

The high rates of future climatic changes, compared with the rates reported for past changes, may hamper species adaptation to new climates or the tracking of suitable conditions, resulting in significant loss of genetic diversity. Trees are dominant species in many biomes and because they are long-lived, they may not be able to cope with ongoing climatic changes. Here, we coupled ecological niche modelling (ENM) and genetic simulations to forecast the effects of climatic changes on the genetic diversity and the structure of genetic clusters. Genetic simulations were conditioned to climatic variables and restricted to plant dispersal and establishment. We used a Neotropical savanna tree as species model that shows a preference for hot and drier climates, but with low temperature seasonality. The ENM predicts a decreasing range size along the more severe future climatic scenario. Additionally, genetic diversity and allelic richness also decrease with range retraction and climatic genetic clusters are lost for both future scenarios, which will lead genetic variability to homogenize throughout the landscape. Besides, climatic genetic clusters will spatially reconfigure on the landscape following displacements of climatic conditions. Our findings indicate that climate change effects will challenge population adaptation to new environmental conditions because of the displacement of genetic ancestry clusters from their optimal conditions.

Mitigation of inbreeding while preserving genetic gain in genomic breeding programs for outbred plants.

Heuristic genomic inbreeding controls reduce inbreeding in genomic breeding schemes without reducing genetic gain. Genomic selection is increasingly being implemented in plant breeding programs to accelerate genetic gain of economically important traits. However, it may cause significant loss of genetic diversity when compared with traditional schemes using phenotypic selection. We propose heuristic strategies to control the rate of inbreeding in outbred plants, which can be categorised into three types: controls during mate allocation, during selection, and simultaneous selection and mate allocation. The proposed mate allocation measure GminF allocates two or more parents for mating in mating groups that minimise coancestry using a genomic relationship matrix. Two types of relationship-adjusted genomic breeding values for parent selection candidates ([Formula: see text]) and potential offspring ([Formula: see text]) are devised to control inbreeding during selection and even enabling simultaneous selection and mate allocation. These strategies were tested in a case study using a simulated perennial ryegrass breeding scheme. As compared to the genomic selection scheme without controls, all proposed strategies could significantly decrease inbreeding while achieving comparable genetic gain. In particular, the scenario using [Formula: see text] in simultaneous selection and mate allocation reduced inbreeding to one-third of the original genomic selection scheme. The proposed strategies are readily applicable in any outbred plant breeding program.

Significant genetic diversity loss following pathogen driven population extinction in the rare endemic Banksia brownii (Proteaceae)

Rapid range-wide extinction of whole populations due to introduced disease would be expected to lead to significant loss of genetic diversity, with impacts being greater for a species that is geographically restricted and with disjunct populations. We investigated the genetic consequences of extirpation in the rare endemic woody shrub, Banksia brownii, following the introduction of the pathogen Phytophthora cinnamomi. B. brownii shows a pattern of disease driven population extinction typical of significant numbers of threatened plant species within south-western Australia. Based on microsatellite genotyping of material from extinct (ex situ seed collections) and extant populations we estimated that 38.2% (gene diversity) and 36.7% (allelic richness) of total genetic diversity, based on contributions of within population variation and differentiation, have been lost from Banksia brownii due to P. cinnamomi. Furthermore, a loss of genetic diversity was reflected in the loss of 16 out of 55 and 6 out of 33 private alleles respectively from two geographically disjunct genetically distinct population groups. We found significant genetic structure within B. brownii with three geographically disjunct population assemblages that should be regarded as separate units for conservation. These findings have been important in developing reintroductions to disease free sites for each conservation unit.

Reconstructing Colonization Dynamics of the Human Parasite Schistosoma mansoni following Anthropogenic Environmental Changes in Northwest Senegal.

BackgroundAnthropogenic environmental changes may lead to ecosystem destabilization and the unintentional colonization of new habitats by parasite populations. A remarkable example is the outbreak of intestinal schistosomiasis in Northwest Senegal following the construction of two dams in the ‘80s. While many studies have investigated the epidemiological, immunological and geographical patterns of Schistosoma mansoni infections in this region, little is known about its colonization history.Methodology/Principal FindingsParasites were collected at several time points after the disease outbreak and genotyped using a 420 bp fragment of the mitochondrial cytochrome c oxidase subunit 1 gene (cox1) and nine nuclear DNA microsatellite markers. Phylogeographic and population genetic analyses revealed the presence of (i) many genetically different haplotypes at the non-recombining mitochondrial marker and (ii) one homogenous S. mansoni genetic group at the recombining microsatellite markers. These results suggest that the S. mansoni population in Northwest Senegal was triggered by intraspecific hybridization (i.e. admixture) between parasites that were introduced from different regions. This would comply with the extensive immigration of infected seasonal agricultural workers from neighboring regions in Senegal, Mauritania and Mali. The spatial and temporal stability of the established S. mansoni population suggests a swift local adaptation of the parasite to the local intermediate snail host Biomphalaria pfeifferi at the onset of the epidemic.Conclusions/SignificanceOur results show that S. mansoni parasites are very successful in colonizing new areas without significant loss of genetic diversity. Maintaining high levels of diversity guarantees the adaptive potential of these parasites to cope with selective pressures such as drug treatment, which might complicate efforts to control the disease.

Genetic diversity in selected stud and commercial herds of the Afrikaner cattle breed

The Afrikaner is one of three indigenous cattle breeds found in South Africa. Afrikaner cattle were originally extensively used for crossbreeding purposes and breed development. The objective of this study was to determine the genetic diversity of selected stud and commercial herds from the whole South African Afrikaner population, as well as to determine the genetic structure among these herds. Assignment methods (based on STRUCTURE software) revealed a real structure consisting of four genetic populations (K = 4). Estimates of genetic diversity did not support the hypothesis of significant loss of genetic diversity in any individual Afrikaner herd. Heterozygosity estimates ranged from 0.456 - 0.737 within individual populations, with an overall heterozygosity estimate of 0.568 for the Afrikaner breed. The average number of alleles per locus was regarded as being 2.67 - 7.78, with an average of 5.18 alleles per locus. It could be concluded that a moderate to high degree of variation is still present within the Afrikaner cattle breed, despite the recent decline in numbers of this indigenous breed.Keywords: Bos taurus africanus, heterozygosity, inbreeding, microsatellite markers

An evaluation of the genetic structure of seed sources and the maintenance of genetic diversity during establishment of two yellow box (Eucalyptus melliodora) seed-production areas

Vegetation clearing and land-use change have depleted many natural plant communities to the point where restoration is required. A major impediment to the success of rebuilding complex vegetation communities is having regular access to sufficient quantities of high-quality seed. Seed-production areas (SPAs) can help generate this seed, but these must be underpinned by a broad genetic base to maximise the evolutionary potential of restored populations. However, genetic bottlenecks can occur at the collection, establishment and production stages in SPAs, requiring genetic evaluation. This is especially relevant for species that may take many years before a return on SPA investment is realised. Two recently established yellow box (Eucalyptus melliodora A.Cunn. ex Schauer, Myrtaceae) SPAs were evaluated to determine whether genetic bottlenecks had occurred between seed collection and SPA establishment. No evidence was found to suggest that a significant loss of genetic diversity had occurred at this stage, although there was a significant difference in diversity between the two SPAs. Complex population genetic structure was also observed in the seed used to source the SPAs, with up to eight groups identified. Plant survival in the SPAs was influenced by seed collection location but not by SPA location and was not associated with genetic diversity. There were also no associations between genetic diversity and plant growth. These data highlighted the importance of chance events when establishing SPAs and indicated that the two yellow box SPAs are likely to provide genetically diverse seed sources for future restoration projects, especially by pooling seed from both SPAs.

Comparison of population genetic estimates amongst wild, F1 and F2 cultured abalone (Haliotis midae)

Haliotis midae is South Africa's most important aquaculture species. The reproduction cycle is currently not closed as many farms rely on wild-caught broodstock for seed production. However, there is an increasing interest in genetic improvement in commercial stocks, with a growing number of producers implementing selective breeding strategies. High throughput commercial production and mass spawning make it difficult to maintain breeding records; therefore, mostly mass selection is practised. The high fecundity and unequal parental contributions also often lead to increased levels of inbreeding. This study therefore aimed to assess the genetic effects of such breeding practices on commercial populations of H. midae. Using microsatellite loci, the genetic properties of a wild, an F1 and an F2 population were estimated and compared. Although there was no significant loss of genetic diversity amongst the cultured populations in comparison with the wild progenitor population, there was low-to-moderate genetic differentiation between populations. Relatedness amongst the F2 population was significant, and the rate of inbreeding was high. The effective population size for the F2 (±50) was also comparatively small with respect to the wild (∞) and F1 (±470) populations. These results suggest that farms need to give caution to breeding practices beyond the first (F1) generation and aim to increase effective population sizes and minimise inbreeding to ensure long-term genetic gain and productivity. This study also confirms the usefulness of population genetic analyses for commercial breeding and stock management in the absence of extensive pedigree records.

Evaluating success of translocations in maintaining genetic diversity in a threatened mammal

The effectiveness of fauna reintroduction programs has been limited by the availability of source animals and the lack of follow up monitoring to assess whether viable populations have been successfully established, particularly in terms of conserving genetic diversity. Here we present genetic assessment of the translocation of golden bandicoots (Isoodon auratus) from a large source population on Barrow Island off the north-west coast of Western Australia to two other island sites and a mainland fenced enclosure. We assessed the genetic diversity of animals translocated to each site and their wild-born progeny, and whether wild-born animals showed evidence of genetic bottlenecks or genetic drift from the source population. Encouragingly, we found no significant loss of genetic diversity in any of the wild-born populations compared to the source population and no significant increase in inbreeding or relatedness amongst wild-born individuals compared to founder populations two years post-translocation. However, we detected an approximately 10-fold reduction in effective population size between founding and wild-born populations. We found no apparent differentiation between wild-born populations and the original source population, or between wild-born animals and their respective founders. Population viability modeling predicts that each of the translocated populations is susceptible to loss of genetic diversity over time. Taken together these results suggest that the golden bandicoot reintroduction program has been initially successful as a result of large founding sizes and high reproductive rates; however, ongoing augmentation will be required to prevent genetic erosion and maintain evolutionary potential in the long-term.

Microsatellite variation in colonizing populations of yellow‐leggedAsian hornet,Vespa velutina nigrithorax, inSouthKorea

AbstractIntroduction of exotic species poses a tremendous challenge to the preservation of original biodiversity and productivity in natural ecosystems. The yellow‐leggedAsian hornetVespa velutina nigrithorax, which is native to tropical/subtropical areas in Indo‐China, was identified in 2003 for the first time inSouthKorea and has established itself in a short period of time. Population genetic study of invasive species may provide exceptional opportunities to test evolutionary theory as well as patterns of colonization from the beginning of the process. Here, the genetic variability of this invasive hornet was examined using seven microsatellites to estimate the propagule pressure and to expect the spreading pathway of this invasive hornet across its range. Overall, there was a significant loss of genetic diversity in its invaded ranges compared to its native range, suggesting that this invasive hornet was introduced via a very small number of propagules. Our results also support that this invasive hornet has experienced a severe bottleneck, as a large reduction was mainly observed in the number of alleles but not in heterozygosity. No significant genetic structuring among populations was found. This study provides baseline information about the current demographic status of the invaded populations, which will help governing agencies prevent further invasions and manage native ecosystems.

From southern refugia to the northern range margin: genetic population structure of the common wall lizard, Podarcis muralis

AbstractAimThermophilic species persisted in southern refugia during the cold phases of the Pleistocene, and expanded northwards during warming. These processes caused genetic imprints, such as a differentiation of genetic lineages and a loss of genetic diversity in the wake of (re)colonization. We used molecular markers and species distribution models (SDMs) to study the impact of range dynamics on the common wall lizard, Podarcis muralis, from southern refugia to the northern range margin.LocationParts of the Western Palaearctic.MethodsWe genotyped 10 polymorphic microsatellites in 282 individuals of P. muralis and sequenced the mitochondrial DNA (mtDNA) cytochrome b gene to study the genetic structure, divergence times and ancestral distributions. Furthermore, we generated SDMs for climate scenarios for 6 and 21 ka derived from two different global circulation models.ResultsWe detected two major mtDNA lineages – a western France clade (Pyrenees to Brittany), and an eastern France clade (southern France to Germany, Belgium and Luxembourg). This split was dated to c. 1.23 Ma. The latter clade was divided into two subclades, which diverged c. 0.38 Ma. Genetic diversity of microsatellites within each clade was nested and showed a significant loss of genetic diversity from south to north, a strong pattern of allele surfing across nearly all loci, and an increase in genetic differentiation towards the northern range margin. Results from SDMs suggest that southward range retraction during the late glacial period split the distribution into geographically distinct refugia.Main conclusionsThe strong genetic differentiation mirrors the effects of long‐term isolation of P. muralis in multiple refugia. Post‐glacial recolonization of Northern Europe has taken place from two distinct refugia, most probably along river systems (Rhône, Rhine, Moselle) and along the Atlantic coastline, with subsequent nested elimination of genetic diversity and increasing genetic differentiation at the northern range margin.

Multiple introductions and no loss of genetic diversity: invasion history of Japanese Rose, Rosa rugosa, in Europe

The shrub Rosa rugosa (Japanese Rose), native to East Asia, is considered one of the most troublesome invasive plant species in natural or semi- natural habitats of northern Europe and has proven very difficult to control. We aimed at disentangling the species' invasion history in Europe, including deter- mining the number of introductions and their geo- graphic origin, and at investigating whether populations in the introduced and native ranges differ in genetic diversity, structure and degree of differentiation. We found that introduced (n = 16) and native (n = 16) populations had similar levels of genetic diversity at seven nuclear SSR (microsatellite) loci. European populations lack isolation by distance and are less genetically differentiated than are populations in East Asia. Multiple and at least three independent coloniza- tion events, one of which was particularly successful, gave rise to current R. rugosa populations in Europe. The geographic distribution patterns of these three genetic clusters could not be explained by natural dispersal alone, indicating that human mediated sec- ondary dispersal is driving the expansion in Europe. One cluster representing three of the European popu- lations was most likely derived from NW Japan, whereas the origin of the remaining thirteen populations could not clearly be resolved. The introduction and expansion in Europe occurred with no significant loss of genetic diversity. We conclude that high propagule pressure at the primary establishment phase is the most parsimonious explanation for this pattern. A potential for long distance seed dispersal, coastal habitat con- nectivity and an outcrossing breeding system are factors likely to have enabled populations of R. rugosa to avoid detrimental effects of genetic bottlenecks and will further increase the species' range size and abundance in Europe. We recommend that human-mediated dis- persal should be prevented in order to halt the continued expansion.

Localized extinction of an arboreal desert lizard caused by habitat fragmentation

We adopted a species’ perspective for predicting extinction risk in a small, endemic, and strictly scansorial lizard (Urosaurus nigricaudus), in an old (∼60year) and highly fragmented (8% habitat remaining) agricultural landscape from the Sonoran Desert, Mexico. We genotyped 10microsatellite loci in 280 individuals from 11 populations in fragmented and continuous habitat. Individual dispersal was restricted to less than 400m, according to analyses of spatial autocorrelation and spatially explicit Bayesian assignment methods. Within this scale, continuous areas and narrow washes with native vegetation allowed high levels of gene flow over tens of kilometers. In the absence of the native vegetation, cleared areas and highways were identified as partial barriers. In contrast, outside the scale of dispersal, cleared areas behaved as complete barriers, and surveys corroborated the species went extinct after a few decades in all small (less than 45ha), isolated habitat fragments. No evidence for significant loss of genetic diversity was found, but results suggested fragmentation increased the spatial scale of movements, relatedness, genetic structure, and potentially affected sex-biased dispersal. A plausible threshold of individual dispersal predicted only 23% of all fragments in the landscape were linked with migration from continuous habitat, while complete barriers isolated the majority of fragments. Our study suggested limited dispersal, coupled with an inability to use a homogeneous and hostile matrix without vegetation and shade, could result in frequent time-delayed extinctions of small ectotherms in highly fragmented desert landscapes, particularly considering an increase in the risk of overheating and a decrease in dispersal potential induced by global warming.