Microsatellite polymorphism and genetic differentiation in three Norwegian populations of Elymus alaskanus (Poaceae)

 Variation at seven microsatellite loci was investigated in three local E. alaskanus populations from Norway and microsatellite variation was compared with allozyme variation. The percentage of polymorphic loci was 81%, the mean number of alleles per polymorphic locus was 5.7 and expected heterozygosity was 0.37. An F-statistic analysis revealed an overall 48% deficit of heterozygotes over Hardy-Weinberg expectations. Gene diversity is mainly explained by the within population component. The averaged between population differentiation coefficient, F _st , over 7 loci is only 0.13, which accounts for only 13% of the whole diversity and was contrary to allozyme analysis. The mean genetic distance between populations was 0.12. However, a χ² -test showed that allele frequencies were different (p < 0.05) among the populations at 5 of the 7 loci. In comparison with the genetic variation detected by allozymes, microsatellite loci showed higher levels of genetic variation. Microsatellite analysis revealed that population H10576 possesses the lowest genetic variation among the tested three populations, which concur with allozyme analysis. The dendrogram generated by microsatellites agreed very well with allozymic data. Our results suggest that natural selection may be an important factor in shaping the genetic diversity in these three local E. alaskanus populations. Possible explanations for deficit heterozygosity and incongruence between microsatellites and allozymes are discussed. Received November 6, 2001; accepted April 24, 2002 Published online: November 14, 2002 Addresses of the authors: Genlou Sun (e-mail: Genlou.sun@STMARYS.CA), Biology Department, Saint Mary's University, Halifax. Nova Scotia, B3H 3C3, Canada. B. Salomon, R. von Bothmer, Department of Crop Science, The Swedish University of Agricultural Sciences, P.O. Box 44, SE-230 53, Alnarp, Sweden.     

Genetic variation and population structure in Scandinavian wolverine (Gulo gulo) populations

Wolverine (Gulo gulo) numbers in Scandinavia were significantly reduced during the early part of the century as a result of predator removal programmes and hunting. Protective legislation in both Sweden and Norway in the 1960s and 1970s has now resulted in increased wolverine densities in Scandinavia. We report here the development of 15 polymorphic microsatellite markers in wolverine and their use to examine the population sub-structure and genetic variability in free-ranging Scandinavian wolverine populations as well as in a sample of individuals collected before 1970. Significant subdivision between extant populations was discovered, in particular for the small and isolated population of southern Norway, which represents a recent recolonization. Overall genetic variability was found to be lower than previously reported for other mustelids, with only two to five alleles per locus and observed heterozygosities (H(O)) ranging from 0.269 to 0.376 across the examined populations, being lowest in southern Norway. Analysis of the mitochondrial DNA control region revealed no variation throughout the surveyed populations. As the historical sample did not show higher levels of genetic variability, our results are consistent with a reduction in the genetic variation in Scandinavian wolverines that pre-dates the demographic bottleneck observed during the last century. The observed subdivision between populations calls for management caution when issuing harvest quotas, especially for the geographically isolated south Norwegian population.     

Nuclear DNA microsatellite analysis of genetic diversity and gene flow in the Scandinavian brown bear (Ursus arctos)

In the 1930s, the Scandinavian brown bear was close to extinction due to vigorous extermination programmes in Norway and Sweden. Increased protection of the brown bear in Scandinavia has resulted in the recovery of four subpopulations, which currently contain close to 1000 individuals. Effective conservation and management of the Scandinavian brown bear requires knowledge of the current levels of genetic diversity and gene flow among the four subpopulations. Earlier studies of mitochondrial DNA (mtDNA) diversity revealed extremely low levels of genetic variation, and population structure that grouped the three northern subpopulations in one genetic clade and the southernmost subpopulation in a second highly divergent clade. In this study, we extended the analysis of genetic diversity and gene flow in the Scandinavian brown bear using data from 19 nuclear DNA microsatellite loci. Results from the nuclear loci were strikingly different than the mtDNA results. Genetic diversity levels in the four subpopulations were equivalent to diversity levels in nonbottlenecked populations from North America, and significantly higher than levels in other bottlenecked and isolated brown bear populations. Gene flow levels between subpopulations ranged from low to moderate and were correlated with geographical distance. The substantial difference in results obtained using mtDNA and nuclear DNA markers stresses the importance of collecting data from both types of genetic markers before interpreting data and making recommendations for the conservation and management of natural populations. Based on the results from the mtDNA and nuclear DNA data sets, we propose one evolutionarily significant unit and four management units for the brown bear in Scandinavia.     

Genetic differentiation in Fomitopsis pinicola (Schwarts: Fr.) Karst studied by means of arbitrary primed-PCR

Generic variation within and among one Finnish and three Swedish populations of Fomitopsis pinicola (Schwarts: Fr.) Karst. were studied by amplifying DNA from hap-loid isolates originating from single spore cultures using two arbitrary primers. Analysis offspring from single fruit bodies revealed only three pairs of codominant alleles among 42 variable genetic markers, the remaining 38 segregated independently. Genetic similarity was measured in terms of Euclidean distance. Individuals in the Finnish population tended to form a distinct cluster in the principal component analysis. Variation within and among populations/regions was partitioned by Analysis of Molecular Variance — AMOVA. Within population variation accounted for 91.6% of the total genetic variation. The remaining 7.68% was accounted for by variation between the Finnish population and each of the three Swedish ones. Variation among the Swedish populations accounted for only 0.72% of the total variation. Wright's F^st was 0.17 for all four populations and 0.13 for the three Swedish populations. These relatively low values indicate that there is gene flow among all populations or that they are derived from a common ancestral population. The observed pattern of genetic variation is probably the result of effective spore dispersal and the continuous distribution of this common early successional species.     

Contrasting patterns of genetic variation and structure in plant invasions of mountains

Aim To assess the population genetic consequences of the colonization of two species with contrasting mating systems, Solidago canadensis and Lactuca serriola, along altitudinal gradients in both their native and introduced ranges. Location Allegheny Mountains, West Virginia and Wallowa Mountains, Oregon, USA; Valais, southern Switzerland. Methods Leaf material was collected from populations along altitudinal gradients and genotyped at seven microsatellite loci for each species. Differences in variability between native and introduced areas and in relation to altitude were analysed using linear models. Differences in the genetic, geographical and altitudinal structure of populations between areas were analysed by AMOVA, cluster analysis and Mantel tests. Results Genetic variation within and across populations of S. canadensis was significantly reduced, while populations of L. serriola were significantly more variable, in the introduced area. Genetic diversity decreased significantly with altitude for S. canadensis but not L. serriola. Genetic structure of S. canadensis was similar in both areas, and populations were isolated by geographical but not altitudinal distance. By contrast, population structure of L. serriola was much weaker in the introduced area, and populations were not isolated by distance in either area. Main conclusions Solidago canadensis has experienced a strong genetic bottleneck on introduction to the Valais, but this has not prevented it from colonizing a wide altitudinal range. Variation in neutral markers is therefore not necessarily a good measure for judging the ecological behaviour of a species. By contrast, the greater variability of L. serriola in the introduced area, where it also occurs over a greater altitudinal range, can be explained by increased outcrossing among admixed populations. This suggests that the ecological amplitude of alien species might be enhanced after population admixture in the new range, especially for species with highly structured native populations. However, even genetically depauperate introduced populations can be expected to colonize the same environmental range that they occupy in the native area.     

Population differentiation in the redshank (<Emphasis Type="Italic">Tringa totanus</Emphasis>) as revealed by mitochondrial DNA and amplified fragment length polymorphism markers

The redshank (Tringa totanus) is declining throughout Europe and to implement efficient conservation measures, it is important to obtain information about the population genetic structure. The aim of the present study was two-fold. First, we analysed the genetic variation within and between populations in the Baltic region in southern Scandinavia. Evidence of genetic structure would suggest that different populations might require separate management strategies. Second, in an attempt to study large-scale genetic structure we compared the Baltic populations with redshanks from northern Scandinavia and Iceland. This analysis could reveal insights into phylogeography and long-term population history. DNA samples were collected from six breeding sites in Scandinavia presumed to include two subspecies (totanus and britannica) and a further sample from Iceland (subspecies robusta). Two methods were used to study the population genetic structure. Domain II and III of the mitochondrial control region was analysed by DNA sequencing and nuclear DNA was analysed by screening amplified fragment length polymorphism (AFLP) markers. Mitochondrial DNA showed no variation between individuals in domain II. When analysing an 481 bp fragment of domain III seven haplotypes were found among birds. On the basis of mtDNA sequences, redshanks showed some evidence of a recent expansion from a bottlenecked refugial population. Bayesian analyses of AFLP data revealed a significant genetic differentiation between suggested subspecies but not between populations within the Baltic region. Our results indicate that populations of redshanks in Europe constitute at least three separate management units corresponding to the recognised subspecies.     

Investigating the genetic load of an emblematic invasive species: the case of the invasive harlequin ladybird Harmonia axyridis

Introduction events can lead to admixture between genetically differentiated populations and bottlenecks in population size. These processes can alter the adaptive potential of invasive species by shaping genetic variation, but more importantly, they can also directly affect mean population fitness either increasing it or decreasing it. Which outcome is observed depends on the structure of the genetic load of the species. The ladybird Harmonia axyridis is a good example of invasive species where introduced populations have gone through admixture and bottleneck events. We used laboratory experiments to manipulate the relatedness among H. axyridis parental individuals to assess the possibility for heterosis or outbreeding depression in F₁ generation offspring for two traits related to fitness (lifetime performance and generation time). We found that inter‐populations crosses had no major impact on the lifetime performance of the offspring produced by individuals from either native or invasive populations. Significant outbreeding depression was observed only for crosses between native populations for generation time. The absence of observed heterosis is indicative of a low occurrence of fixed deleterious mutations within both the native and invasive populations of H. axyridis. The observed deterioration of fitness in native inter‐population crosses most likely results from genetic incompatibilities between native genomic backgrounds. We discuss the implications of these results for the structure of genetic load in H. axyridis in the light of the available information regarding the introduction history of this species.     

Population structure of <Emphasis Type="Italic">Nouelia insignis</Emphasis> (Asteraceae), an endangered species in southwestern China,based on chloroplast DNA sequences: recent demographic shrinking

Nouelia insignis, an endangered species, is distributed in the Jinsha and Nanpan drainage areas in southwestern China. In this study, we examined the genetic diversity and population structure based on the sequences of the cpDNA rpL 16 intron. Low levels of genetic variation were detected within all populations of the endemic species. A gene genealogy of 11 haplotypes recovered two major lineages I and II, with haplotypes H1 and H6 nested as interior nodes, respectively. Haplotype H1 was widespread in all populations, while haplotype H6 was restricted to populations southern of the Jinsha River. Low levels of genetic differentiation were detected, as most F _st values between populations were zero. This result, however, contradicts previous studies based on allozymes and fingerprinting. Genetic analyses suggested that coancestry due to low evolutionary rates resulted in the lack of geographical subdivision. Molecular dating estimated that the two lineages split about 3.224 MYA (95% CI 1.070–6.089 MYA). Maintenance of ancestral polymorphisms was possibly attributable to a long-standing large effective population size until recently. Postglacial demographic expansion was supported by a unimodal mismatch distribution and star-like phylogenies.     

Single Versus Multiple Sources of Introduced Populations Identified With Molecular Markers: A Case Study of a Freshwater Fish

The presence of a widespread exotic raises the question as to whether the successful invasion can be attributed to spread after a single introduction or is the product of multiple introductions. The plains killifish, Fundulus zebrinus, is native to the western Great Plains of the United States but is also found throughout the Colorado River basin. We surveyed five introduced populations for genetic variation in allozymes and mitochondrial DNA (mtDNA) in order to compare the genetic structure of these populations with those from across the native range. Our survey revealed two genetically distinct stocks of introduced F. zebrinus, one in the San Juan and one in the Yampa and Colorado drainages. Each stock corresponds to at least one unique introduction event. In addition, data available from a genetic survey of the native range allowed us to identify the sources of these introduced populations. The combination of allozyme and mtDNA data for the San Juan population indicated that the most probable source for this population was the Pecos drainage of New Mexico and Texas. The Yampa and Colorado populations seem to be derived from the western Arkansas drainage, although the allozyme data indicated that another nearby drainage(s) might have also served as a source for the Colorado population.     

Origin of clonal diversity in triploid parthenogenetic Trichoniscus pusillus pusillus (Isopoda,Crustacea) based upon allozyme and nucleotide sequence data

Variation in PGM (phosphoglucomutase) and MDH (malate dehydrogenase) allozymes and in mitochondrial and nuclear (ribosomal) DNA gives evidence of at least three independent origins of triploid Trichoniscus pusillus pusillus. Much of the genetic variation found may reflect variation within the parental diploid population(s), but it is argued that some of the variation in PGM allozymes have accumulated within the parthenogenetic lines. Based upon the variation at this locus, 15 genetically distinct clones are distinguished.     

High levels of genetic diversity in marginal populations of the marsh orchid Dactylorhiza majalis subsp. majalis

Because of harsh conditions, suboptimal habitat quality and poor connectivity to other populations, plant populations at the margin of a distribution are expected to be less genetically diverse, but to be more divergent from each other than populations in the centre of a distribution. In northern Europe, northern marginal populations may also be younger than populations further to the south, and may have had less time to accumulate genetic diversity by mutation and gene flow. However, orchids have very small seeds, which are easily dispersed long distances by wind, and orchids are therefore expected to show less differentiation between marginal and central populations than other groups of seed plants. Here, we analysed whether Scandinavian populations of the tetraploid marsh orchid Dactylorhiza majalis subsp. majalis differ from central European populations in genetic diversity patterns. A total of 220 plants from eight central European and ten Scandinavian populations was examined for variation at five nuclear microsatellite loci, nuclear ITS and 13 polymorphic sites in noncoding regions of the plastid genome. The total genetic diversity was slightly lower in Scandinavia than in central Europe, both in plastid and nuclear markers, but the differences were small. Also, the Scandinavian populations were less diverse and somewhat more strongly differentiated from each other than the central European ones. Dactylorhiza majalis subsp. majalis has apparently colonized Scandinavia on multiple independent occasions and from different source areas in the south. Seed flow between Scandinavian populations has still not fully erased the patterns imprinted by early colonization. Our results suggest that marginal populations of orchids may be as important as central ones in preserving genetic diversity through Pleistocene glacial cycles. We also predict that orchids with their light seeds are better adapted than many other plants to respond to future climate changes by dispersing into new suitable areas.     

GENETIC VARIATION AMONG STRAINS OF THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM (DINOPHYCEAE)

The toxic dinoflagellate Gymnodinium catenatum Graham has formed recurrent toxic blooms in southeastern Tasmanian waters since its discovery in the area in 1986. Current evidence suggests that this species might have been introduced to Tasmania prior to 1973, possibly in cargo vessel ballast water carried from populations in Japan or Spain, followed by recent dispersal to mainland Australia. To examine this hypothesis, cultured strains from G. catenatum populations in Australia, Spain, Portugal, and Japan were examined using allozymes and randomly amplified polymorphic DNA (RAPD). Allozyme screening detected very limited polymorphism and was not useful for population comparisons; however, Australian, Spanish, Portuguese, and Japanese strains showed considerable RAPD diversity, and all strains examined represented unique genotypes. Multidimensional scaling analysis (MDS) of RAPD genetic distances between strains showed clear separation of strains into three nonoverlapping regional clusters: Australia, Japan, and Spain/Portugal. Analysis of genetic distances between strains from the three regional populations indicated that Australian strains were almost equally related to both the Spanish/Portuguese population and the Japanese population. Analysis of molecular variance (AMOVA) found that genetic variation was partitioned mainly within populations (87%) compared to the variation between the regions (8%) and between populations within regions (5%). The potential source population for Tasmania’s introduced G. catenatum remains equivocal; however, strains from the recently discovered mainland Australian population (Port Lincoln, South Australia, 1996) clustered with Tasmanian strains, supporting the notion of a secondary relocation of Tasmanian G. catenatum populations to the mainland via a shipping vector. Geographic and temporal clustering of strains was evident among the Tasmanian strains, indicating that genetic exchange between neighboring estuaries is limited and that Tasmanian G. catenatum blooms are composed of localized, estuary-bound subpopulations.     

Multilocus phylogeography and population structure of common eiders breeding in North America and Scandinavia

Aim Glacial refugia during the Pleistocene had major impacts on the levels and spatial apportionment of genetic diversity of species in northern latitude ecosystems. We characterized patterns of population subdivision, and tested hypotheses associated with locations of potential Pleistocene refugia and the relative contribution of these refugia to the post‐glacial colonization of North America and Scandinavia by common eiders (Somateria mollissima). Specifically, we evaluated localities hypothesized as ice‐free areas or glacial refugia for other Arctic vertebrates, including Beringia, the High Arctic Canadian Archipelago, Newfoundland Bank, Spitsbergen Bank and north‐west Norway. Location Alaska, Canada, Norway and Sweden. Methods Molecular data from 12 microsatellite loci, the mitochondrial DNA (mtDNA) control region, and two nuclear introns were collected and analysed for 15 populations of common eiders (n = 716) breeding throughout North America and Scandinavia. Population genetic structure, historical population fluctuations and gene flow were inferred using F‐statistics, analyses of molecular variance, and multilocus coalescent analyses. Results Significant inter‐population variation in allelic and haplotypic frequencies were observed (nuclear DNA F_ST = 0.004–0.290; mtDNA Φ_ST = 0.051–0.927). Whereas spatial differentiation in nuclear genes was concordant with subspecific designations, geographic proximity was more predictive of inter‐population variance in mitochondrial DNA haplotype frequency. Inferences of historical population demography were consistent with restriction of common eiders to four geographic areas during the Last Glacial Maximum: Belcher Islands, Newfoundland Bank, northern Alaska and Svalbard. Three of these areas coincide with previously identified glacial refugia: Newfoundland Bank, Beringia and Spitsbergen Bank. Gene‐flow and clustering analyses indicated that the Beringian refugium contributed little to common eider post‐glacial colonization of North America, whereas Canadian, Scandinavian and southern Alaskan post‐glacial colonization is likely to have occurred in a stepwise fashion from the same glacial refugium. Main conclusions Concordance of proposed glacial refugia used by common eiders and other Arctic species indicates that Arctic and subarctic refugia were important reservoirs of genetic diversity during the Pleistocene. Furthermore, suture zones identified at MacKenzie River, western Alaska/Aleutians and Scandinavia coincide with those identified for other Arctic vertebrates, suggesting that these regions were strong geographic barriers limiting dispersal from Pleistocene refugia.     

Genetic variability and structure of the water vole Arvicola amphibius across four metapopulations in northern Norway

Water vole Arvicola amphibius populations have recently experienced severe decline in several European countries as a consequence of both reduction in suitable habitat and the establishment of the alien predator American mink Neovison vison. We used DNA microsatellite markers to describe the genetic structure of 14 island populations of water vole off the coast of northern Norway. We looked at intra‐ and inter‐population levels of genetic variation and examined the effect of distance among pairs of populations on genetic differentiation (isolation by distance). We found a high level of genetic differentiation (measured by F_ST) among populations overall as well as between all pairs of populations. The genetic differentiation between populations was positively correlated with geographic distance between them. A clustering analysis grouped individuals into 7 distinct clusters and showed the presence of 3 immigrants among them. Our results suggest a small geographic scale for evolutionary and population dynamic processes in our water vole populations.     

Low genetic variation support bottlenecks in Scandinavian red deer

Loss of genetic variation from genetic drift during population bottlenecks has been shown for many species. Red deer (Cervus elaphus) may have been exposed to bottlenecks due to founder events during postglacial colonisation in the early Holocene and during known population reductions in the eighteenth and nineteenth centuries. In this study, we assess loss of genetic variation in Scandinavian red deer due to potential bottlenecks by comparing microsatellite (n = 14) and mitochondrial DNA variation in the Norwegian and Swedish populations with the Scottish, Lithuanian and Hungarian populations. Bottlenecks are also assessed from the M ratio of populations, heterozygosity excess and from hierarchical Bayesian analyses of their demographic history. Strong genetic drift and differentiation was identified in both Scandinavian populations. Microsatellite variation was lower in both Scandinavian populations compared with the other European populations and mitochondrial DNA variation was especially low in the Swedish population where only one unique haplotype was observed. Loss of microsatellite alleles was demonstrated by low M ratios in all populations except the Hungarian. M ratios’ were especially low in the Scandinavian populations, indicating additional or more severe bottlenecks. Heterozygosity excess compared with the expectation from the number of observed microsatellite alleles suggested a recent bottleneck of low severity in the Norwegian population. Hierarchical Bayesian coalescent analyses consistently yielded estimates of a large ancestral and a small current population size in all investigated European populations and suggested the onset of population decline to be between 5,000 and 10,000 years ago, which coincide well with postglacial colonisation.     

GENETIC DRIFT AND FOUNDER EFFECT IN NATIVE VERSUS INTRODUCED POPULATIONS OF AN INVADING PLANT,LYTHRUM SALICARIA (LYTHRACEAE)

There are few convincing examples of genetic drift at loci under selection in natural populations. The plant sexual polymorphism tristyly provides an opportunity to investigate genetic drift because stochastic processes interacting with frequency-dependent selection give rise to a diagnostic pattern of morph-frequency variation. A previous study of 102 Ontario populations of the introduced tristylous wetland herb Lythrum salicaria provided evidence for the role of stochastic processes during colonization. However, whether stochastic effects are greater in these recently introduced populations compared to native Eurasian populations remains unclear. The propensity of this species to invade disturbed habitats suggests that episodes of colonization and periods of small population size must also occur in the native range. A survey of 102 populations in southwestern France indicated reduced stochastic effects in native populations. Populations exhibited significantly lower morph loss than in Ontario (5% vs. 23%) and significantly higher values of morph evenness. The greater incidence of trimorphism in French populations was not associated with larger population sizes; populations were significantly smaller than those in Ontario (means: 266 vs. 487). Morph evenness was positively correlated with population size among French but not Ontario populations, providing further evidence of nonequilibrium conditions in introduced compared to native populations. The incidence of trimorphism was unexpectedly high in small native populations (N ≤ 25; 22 of 27 populations trimorphic). Computer simulations indicated that levels of gene flow on the order of m ≥ 0.05 can account for the maintenance of tristyly in small populations. The high connectivity of populations within the agricultural landscape typical of southwestern France may facilitate levels of gene flow sufficient to maintain trimorphism in small populations.     

Genetic variation in Scandinavian Anthericum liliago (Anthericaceae): allopolyploidy, hybridization and immigration history

 We investigated patterns of isozyme variation and the hierarchic structure of genetic diversity in 25 Scandinavian populations of the lilioid herb, Anthericum liliago. Isozyme data suggest that tetraploid A. liliago has an allopolyploid origin and that A. ramosum may be one of its diploid progenitors. Two populations contained known or suspected hybrids between A. liliago and A. ramosum. Isozymes show that one population from S Sweden contains both triploid (hybrid) and tetraploid individuals whereas a putatively hybrid Danish population represents diploid A. liliago. There is an overall northward and eastward decline in allelic richness in the tetraploid populations, with the highest numbers of alleles in Denmark and SW Sweden. This pattern is consistent with a progressive loss of allelic variation during the species' postglacial colonization of Scandinavia. The between-population component of genetic diversity is 4% (compared with 12% in diploid A. ramosum), the between-region diversity component is 7% and 89% of the total diversity is stored within populations. Received March 13, 2002; accepted September 24, 2002 Published online: December 11, 2002     

EFFECTS OF INTRINSIC AND EXTRINSIC FACTORS ON POPULATION FRAGMENTATION IN THREE SPECIES OF NORTH AMERICAN MINNOWS (TELEOSTEI: CYPRINIDAE)

Geographic patterns of genetic variation (mitochondrial DNA [mtDNA] and allozymes) were used to examine effects of intrinsic characteristics (e.g., vagility, habitat specificity, and reproductive behaviors) and extrinsic factors (e.g., climatic and geological history) on population fragmentation. The three species of cyprinid fishes examined (Tiaroga cobitis, Meda fulgida, and Agosia chrysogaster) occupied similar historical ranges within the lower Colorado River drainage, but differ in intrinsic characteristics conducive to population fragmentation. Relationships among populations were similar across species, reflecting common historical influences, but results indicate the distribution of variation among species is strongly affected by intrinsic characteristics. Variation within two species (T. cobitis and M. fulgida) is subdivided among populations, suggesting little gene flow among rivers. In contrast, similarity of A. chrysogaster populations throughout the Gila River drainage supports the hypothesis that levels of gene flow are high for this species. Levels of mtDNA divergence were much higher than expected for both T. cobitis and A. chrysogaster suggesting long-term isolation of geographic regions. These results indicate that both long-term and short-term extrinsic factors have shaped basic patterns of variation within these fishes; however, the intrinsic characteristics of each species have strongly affected the population genetic structure of these fishes.     

Microsatellite and major histocompatibility complex variation in an endangered rattlesnake,the Eastern Massasauga (Sistrurus catenatus)

Genetic diversity is fundamental to maintaining the long‐term viability of populations, yet reduced genetic variation is often associated with small, isolated populations. To examine the relationship between demography and genetic variation, variation at hypervariable loci (e.g., microsatellite DNA loci) is often measured. However, these loci are selectively neutral (or near neutral) and may not accurately reflect genomewide variation. Variation at functional trait loci, such as the major histocompatibility complex (MHC), can provide a better assessment of adaptive genetic variation in fragmented populations. We compared patterns of microsatellite and MHC variation across three Eastern Massasauga (Sistrurus catenatus) populations representing a gradient of demographic histories to assess the relative roles of natural selection and genetic drift. Using 454 deep amplicon sequencing, we identified 24 putatively functional MHC IIB exon 2 alleles belonging to a minimum of six loci. Analysis of synonymous and nonsynonymous substitution rates provided evidence of historical positive selection at the nucleotide level, and Tajima's D provided support for balancing selection in each population. As predicted, estimates of microsatellite allelic richness, observed, heterozygosity, and expected heterozygosity varied among populations in a pattern qualitatively consistent with demographic history and abundance. While MHC allelic richness at the population and individual levels revealed similar trends, MHC nucleotide diversity was unexpectedly high in the smallest population. Overall, these results suggest that genetic variation in the Eastern Massasauga populations in Illinois has been shaped by multiple evolutionary mechanisms. Thus, conservation efforts should consider both neutral and functional genetic variation when managing captive and wild Eastern Massasauga populations.     

Significant genetic admixture after reintroduction of peregrine falcon (<Emphasis Type="Italic">Falco peregrinus</Emphasis>) in Southern Scandinavia

The peregrine falcon (Falco peregrinus) population in southern Scandinavia was almost extinct in the 1970’s. A successful reintroduction project was launched in 1974, using captive breeding birds of northern and southern Scandinavian, Finnish and Scottish origin. We examined the genetic structure in the pre-bottleneck population using eleven microsatellite markers and compared the data with the previously genotyped captive breeding population and contemporary wild population. Museum specimens between 53 and 130 years old were analyzed. Despite an apparent loss of historical genetic diversity, the contemporary population shows a relatively high level of genetic variation. Considerable gene introgression from captive breeding stock used to repopulate the former range of southern Scandinavian peregrines may have altered the genetic composition of this population. Both the historical and contemporary northern and southern Scandinavian populations are genetically differentiated. The reintroduction project implemented in the region and the use of non-native genetic stock likely prevented the southern Scandinavian population from extinction and thus helped maintain the level of genetic diversity and prevent inbreeding depression. The population is rapidly increasing in numbers and range and shows no indication of reduced fitness or adaptive capabilities in the wake of the severe bottleneck and the reintroduction.