Genetic population structure of the vulnerable bog fritillary butterfly

Populations of the bog fritillary butterfly Proclossiana eunomia (Lepidoptera, Nymphalidae) occur in patchy habitat in central and western Europe. P. eunomia is a vulnerable species in the Belgian Ardennes and the number of occupied sites has significantly decreased in this region since the 1960s. RAPD (random amplified polymorphic DNA) markers were used to study the consequences of habitat loss and fragmentation on the genetic population structure of this species. Gene diversity was lower in populations with smaller population sizes. Genetic subdivision was high (Fst=0.0887) considering the small spatial scale of this study (150 km2). The most geographically isolated population was also the most genetically differentiated one. The genetic population structure and genetic differentiation detected in this study were explained by (1) differences in altitude of the sampled locations and, (2) lower dispersal propensity and dispersal rate in fragmented landscapes versus continuous landscapes. Results from the RAPD analyses were compared with a previous allozyme based study on the same populations. The results of this study suggest that increased fragmentation has lead to a greater genetic differentiation between remaining P. eunomia populations.     

A preliminary investigation of allozyme genetic variation and population structure in common pandora (<Emphasis Type="Italic">Pagellus erythrinus</Emphasis>, Sparidae) from Tunisian and Libyan coasts

The genetic characterization of natural populations of common pandora (Pagellus erythrinus, Sparidae) was studied using allozyme markers. Fish samples (n = 360) were collected from five locations along the Tunisian coasts and one from the Libyan coast. From eight enzymatic systems, 12 putative enzyme-coding loci were resolved, 8 of which were polymorphic at a level of 99%. F statistics indices revealed a significant departure from panmixia with heterozygote deficiencies and a slight genetic differentiation between samples. Neighbor-joining dendrogram constructed by Reynolds genetic distance showed that the populations sampled from the southeastern Mediterranean Sea were more differentiated from the others.     

Genetic structure of the widespread and common Mediterranean bryophyte Pleurochaete squarrosa (Brid.) Lindb. (Pottiaceae) - evidence from nuclear and plastidic DNA sequence variation and allozymes

The Mediterranean Basin as one the world's most biologically diverse regions provides an interesting area for the study of plant evolution and spatial structure in plant populations. The dioecious moss Pleurochaete squarrosa is a widespread and common bryophyte in the Mediterranean Basin. Thirty populations were sampled for a study on molecular diversity and genetic structure, covering most major islands and mainland populations from Europe and Africa. A significant decline in nuclear and chloroplast sequence and allozyme variation within populations from west to east was observed. While DNA sequence data showed patterns of isolation by distance, allozyme markers did not. Instead, their considerable interpopulation genetic differentiation appeared to be unrelated to geographic distance. Similar high values for coefficients of gene diversity (G(ST)) in all data sets provided evidence of geographic isolation and limited gene flow among populations (i) within islands, (ii) within mainland areas, and (iii) between islands and mainland. Notably, populations in continental Spain are strongly genetically isolated from all other investigated areas. Surprisingly, there was no difference in gene diversity and G(ST) between islands and mainland areas. Thus, we conclude that large Mediterranean islands may function as 'mainland' for bryophytes. This hypothesis and its implication for conservation biology of cryptogamic plants warrant further investigation. While sexually reproducing populations were found all over the Mediterranean Basin, high levels of multilocus linkage disequilibrium provide evidence of mainly vegetative propagation even in populations where sexual reproduction was observed.     

Founder events as determinants of within-island and among-island genetic structure of Daphnia metapopulations

The genetic structure of metapopulations offers insights into the genetic consequences of local extinction and recolonization. We studied allozyme variation in rock pool metapopulations of two species of waterfleas (Daphnia) with the aim to understand how these dynamics influence genetic differentiation. We screened 138 populations of D. magna and 65 populations of D. longispina from an area in the archipelago of southern Finland. The pools from which they were sampled are separated by distances between 1.5 and 4710 m and located on a total of 38 islands. The genetic population structure of the two species was strikingly similar, consistent with their similar metapopulation ecology. The mean F(PT) value (differentiation among pools with respect to the total metapopulation) was 0.55 and a hierarchical analysis showed that genetic differentiation was strong (>0.25) among pools within islands as well as among whole islands. Within islands, pairwise genetic differentiation increased with geographic distance, indicating isolation by distance due to spatially limited dispersal. Previous studies have shown strong founder events occurring during colonization in our metapopulation. We suggest that the genetic population structure in the studied metapopulations is largely explained by three consequences of these founder events: (i) strong drift during colonization, (ii) local inbreeding, which results in hybrid vigour and increased effective migration rates after subsequent immigration, and (iii) effects of selection through hitchhiking of neutral genes with linked loci under selection.     

Genetic variability, population size and isolation of distinct populations in the freshwater fish Cottus gobio L.

Analysis of allozyme data of the European freshwater fish Cottus gobio showed marked genetic differentiation across drainage basins in northeastern Bavaria, which points to the existence of at least two cryptic taxa. Genetic variability within populations differed significantly between these two taxa, which could be due to historical (bottlenecks) or ecological reasons (population size). To distinguish between these two hypotheses we sampled 12 distinct populations from Rhine, Elbe and Danube drainages. Using allozyme data we examined the influence of population size and isolation on genetic variability within populations. We used spatial extent of populations (patch size) as a measure for population size. To estimate isolation we calculated a compound measure which took into account patch size and distance to all neighbouring populations. Both patch size and isolation were highly correlated with genetic variability, explaining ≈95% of the variance of genetic variability within populations. Furthermore, analysis of covariance suggests that the difference in genetic variability between taxa may be explained by differences in population size.     

An exploratory analysis of geographic genetic variation in southern African nyala (Tragelaphus angasii)

We report patterns of genetic variation based on microsatellite, allozyme and mitochondrial control region markers in nyala from geographic locations sampled in South Africa, Mozambique, Malawi and Zimbabwe. Highly significant differences were observed among allele frequencies at three microsatellite loci between populations from KwaZulu-Natal, Limpopo and Malawi, with the Malawi and KwaZulu-Natal groupings showing the highest differentiation (R_ST=0.377). Allozyme frequencies showed minor, non-statistically significant regional differences among the South African populations, with maximum F_ST values of 0.048–0.067. Mitochondrial DNA analyses indicated a unique haplotype in each location sampled. Since none of these indices of population differentiation showed significant correlation to absolute geographic distance, we conclude that geographic variation in this species is probably a function of a distribution pattern stemming from habitat specificity. It is suggested that translocations among geographically distant regional populations be discouraged at present, pending a more elaborate investigation. Transfer of native individuals among local populations may, however, be required for minimizing the likelihood of inbreeding depression developing in small captive populations.     

Patterns of Genetic Population Differentiation in Four Species of Amazonian Frogs: A Test of the Riverine Barrier Hypothesis1

Patterns and levels of allozyme variation among populations of Amazonian frogs were used to test the riverine barrier hypothesis of species differentiation. Two frog species were sampled from each of the two main forest habitats on both banks of the Juruá River in the southwestern Brazilian Amazon Basin at various points along its course to contrast different barrier strengths. Scarthyla ostinodactyla and Scinax rubra were sampled from flooded forest (varzea), and Physalaemus petersi and Epipedobates femoralis from non-flooded forest (terra firme). All species showed high levels of within-population genetic variation. Average Nei's (1978) and Rogers’ (1972) genetic distances between sampled sites for all species were high indicating substantial among-population differentiation. The observation of low gene flow between sampled sites within species was further substantiated with Slatkin's (1993) M? analyses. Randomization tests suggested that there was some population structure at a few assayed polymorphic loci that was consistent with the riverine barrier hypothesis. However, it was apparent from the raw allozyme frequency data that these results were largely driven by substantial differentiation at one or a few collecting localities rather than by basin-wide patterns of riverine differentiation. Phenograms using genetic distance matrices supported this interpretation. Patterns of geographic variation are probably more consistent with the idea of this region being a zone of secondary contact.     

Distribution and biomass of microphytes measured by benthic chlorophyll a in a tropical lagoon (New Caledonia,South Pacific)

Starch-gel electrophoretic techniques were applied to the investigation of molecular genetic variation in populations of the rough periwinkle Littorina saxatilis. The investigation comprised two phases: a) technique development to resolve as many as possible of the allozyme loci reported in the literature as having been screened in the genus Littorina and in Melarhaphe neritoides; b) the use of these loci to assess levels of genetic variation in and patterns of genetic differentiation among populations of L. saxatilis from a relatively isolated group of populations from Galway Bay, Ireland. More than 43 allozyme loci (of which four were screened for the first time here in this species), coding for 37 enzymes, were investigated and thirteen of these loci (including two loci screened for the first time here) were found to be variable and reliably scorable. Samples from five pairs of transects were collected from Inismór, Aran Islands, from sites with known exposure levels; one transect within each pair was collected from an exposed site and the other from a nearby, but relatively sheltered site. UPGMA for eleven loci, (ARK and PGDH were excluded from cluster and FST analysis as they were unscorable in a few samples), showed that the samples cluster mostly by pair, reflecting their geographic origin and is indicative of little gene flow between populations. Levels of population differentiation were high among samples from the top of the shore, but unusually so at AAT-1 which showed nearly three times the mean FST value for the eleven loci. There was also a significant regression of frequency of AAT-1100 against level of exposure. In addition, among midshore samples, there was a consistently higher frequency of AAT-1100 in sheltered habitats. These results support the findings of others, indicating that this locus may be subject to natural selection.     

Differentiation of chum salmon Oncorhynchus keta Wallbaum populations as revealed with microsatellite and allozyme markers: A comparative study

The features and extent of population differentiation in chum salmon Oncorhynchus keta from Sakhalin and Iturup Islands were studied with 10 microsatellite and 12 allozyme markers. It was demonstrated with the example of allozyme polymorphism at the EstD locus that the effect of an individual locus with one major allele is capable of distorting the total picture of population differentiation. Multiallelic microsatellites were more efficient in revealing the genetic structure of chum salmon populations at the levels of differences between regional populations and between the stocks of individual rivers of the same region.     

Differentiation of chum salmon Oncorhynchus keta Walbaum populations as revealed with microsatellite and allozyme markers: a comparison

The character and extent of population differentiation in chum salmon Oncorhynchus keta from Sakhalin and Iturup were comparatively studied with 10 microsatellite and 12 allozyme markers. It was demonstrated with the example of allozyme polymorphism at the EstD locus that the effect of an individual locus with one major allele is capable of distorting the total picture of population differentiation. Multiallelic microsatellites were more efficient in revealing the genetic structure of chum salmon populations at the levels of differences between regional populations and between the stocks of individual rivers of the same region.     

The structure of allozyme and leaf shape variation in isolated, range-margin populations of the shrub Hippocrepis emerus (Leguminosae)

We investigated allozyme variation and phenotypic variation in leaf shape in 15 populations of the shrub Hippocrepis emerus (Leguminosae) from the three isolated, regional populations in Scandinavia and analysed patterns of differentiation and the hierarchical structuring of diversity on different geographic scales There are pronounced geographic differences between the Norwegian and Swedish isolates of the species and most of the polymorphic allozyme loci show reciprocal fixation in the two isolates The Scandinavian populations of H emerus are not only disjunct on a macrogeographic scale but also show considerable disjunction within regions Within the Oland regional population, a central group of populations shows low levels of Inter-population differentiation the Gotland group of populations is related to this core group of Oland populations The geographically marginal populations on Oland are spatially isolated and show a higher degree of divergence between populations than does the central group of Oland populations We interpret genetic divergence between the marginal populations in terms of genetic drift - as a result of historical fluctuations in habitat availability and population size     

Genetic structure of Brandt’s vole (<Emphasis Type="Italic">Lasiopodomys brandtii</Emphasis>) populations in Inner Mongolia,China, based on microsatellite analysis

Brandt’s vole (Lasiopodomys brandtii) distribution is discontinuous in Inner Mongolia with some populations isolated from others. Recently, some isolated populations have suffered extinction, and the factors responsible remain elusive. Genetic drift is one of the processes affecting population genetic differentiation, and can play a substantial role in the divergence of small, isolated populations. Using seven microsatellite markers, we genotyped four geographically isolated populations of Brandt’s vole, all of which exhibit episodic fluctuations in population density. The results showed a strong genetic differentiation among the geographically distinct populations (total F _ST = 0.124) and in particular, one population (Zhengxiangbaiqi) was isolated from all others (F _ST values were greatest between Zhengxiangbaiqi and other populations). Furthermore, high levels of inbreeding (F _IS values ranged from 0.205 to 0.290) within each distinct population suggest that inbreeding has and is likely occurring in Brandt’s vole populations. These processes can decrease average individual fitness and consequently increase the risk of extinction of the species.     

A microsatellite-based estimation of clonal diversity and population subdivision in Zostera marina, a marine flowering plant

We examined the genetic population structure in eelgrass (Zostera marina L.), the dominant seagrass species of the northern hemisphere, over spatial scales from 12 km to 10 000 km using the polymorphism of DNA microsatellites. Twelve populations were genotyped for six loci representing a total of 67 alleles. Populations sampled included the North Sea (four), the Baltic Sea (three), the western Atlantic (two), the eastern Atlantic (one), the Mediterranean Sea (one) and the eastern Pacific (one). Microsatellites revealed substantial genetic variation in a plant group with low allozyme diversity. Average expected heterozygosities per population (monoclonal populations excluded) ranged from 0.32 to 0.61 (mean = 0. 48) and allele numbers varied between 3.3 and 6.7 (mean = 4.7). Using the expected frequency of multilocus genotypes within populations, we distinguished ramets from genetic individuals (i.e. equivalent to clones). Differences in clonal diversity among populations varied widely and ranged from maximal diversity (i.e. all ramets with different genotype) to near or total monoclonality (two populations). All multiple sampled ramets were excluded from further analysis of genetic differentiation within and between populations. All but one population were in Hardy-Weinberg equilibrium, indicating that Zostera marina is predominantly outcrossing. From a regression of the pairwise population differentiation with distance, we obtained an effective population size Ne of 2440-5000. The overall genetic differentiation among eelgrass populations, assessed as rho (a standardized estimate of Slatkin's RST) was 0.384 (95% CI 0.34-0.44, P < 0.001). Genetic differentiation was weak among three North Sea populations situated 12-42 km distant from one another, suggesting that tidal currents result in an efficient exchange of propagules. In the Baltic and in Nova Scotia, a small but statistically significant fraction of the genetic variance was distributed between populations (rho = 0.029-0. 053) at scales of 15-35 km. Pairwise genetic differentiation between European populations were correlated with distance between populations up to a distance of 4500 km (linear differentiation-by-distance model, R2 = 0.67). In contrast, both Nova Scotian populations were genetically much closer to North Sea and Baltic populations than expected from their geographical distance (pairwise rho = 0.03-0.08, P < 0.01). A biogeographical cluster of Canadian with Baltic/North Sea populations was also supported using a neighbour-joining tree based on Cavalli-Sforza's chord distance. Relatedness between populations may be very different from predictions based on geographical vicinity.     

Microgeographic variation in allozyme and shell characters in Littorina saxatilis Olivi (Prosobranchia: Littorinidae)

Twenty-three enzymes and five shell parameters were screened in 11 subpopulations of Littorina saxatilis Olivi (= L. rudis Maton) occupying different habitats over a 1 km stretch of coastline. Shell morphology varied considerably and consistently with respect to degree of exposure, and since there is evidence that such morphology is at least partly under genetic control, it is likely that natural selection selects particular genotypes at particular locations. There was significant allozyme heterogeneity between neighbouring subpopulations, sometimes only metres apart, but little of the allozyme variability could be related directly to environmental pressures. Thus, with the exception of the Odh locus, the considerable morphological differentiation between snails from exposed and sheltered sites was not reflected in differentiation of those genes coding for electrophoretically assayed enzymes. At the Odh locus, virtually all the genetic differentiation between subpopulations was attributable to differentiation between habitat types. Two loci, Sod-1 and Aat-1, showed highly significant genetic disequilibrium, and possible reasons for this are explored. The population structure as assessed electrophoretically accords well with the stepping-stone model which permits greater differentiation of neighbouring populations than the island model, and which seems realistic in the ovoviviparously reproducing L. saxatilis, where the greater part of gene flow is likely to occur through the occasional migration of adults between contiguous populations.     

Allozyme diversity in relation to geographic distribution and population size inLathyrus vernus (L.) Bernh. (Fabaceae)

Lathyrus vernus (L.) Bernh. is a diploid, long-lived perennial and insect-pollinated herb with no special adaptation to long-distance dispersal. It occurs on neutral soil in deciduous forests throughout western Eurasia. Due to specific habitat preferences,L. vernus has a fragmented distribution with isolated populations. We investigated allozyme variation at eleven loci in 20 populations ofL. vernus from one geographically central region (the Czech Republic and the Slovak Republic) and two geographically marginal regions (southern and central Sweden) in the species present-day distribution. There was a clear differentiation between the three regions and the genetic distance between the populations was highly correlated with geographic distance. The total genetic diversity (H_T) was 0.354. The proportion of genetic diversity due to differentiation between regions, and to differentiation between populations within regions, accounted for 10% each. There was no difference in level of genetic diversity between the three regions. No significant difference in level of genetic diversity was found between small and large populations. The genetic diversity inL. vernus may either be a result of the long generation-time of the species or peculiarities in the post-glacial migration species, e.g. survival only in refugia far east of the sampled populations and/or migration as a continuous process not involving founder-events.     

Gene flow versus selection pressure and ancestral differentiation in the composition of species: Analysis of populational variation ofJuniperus ashei buch. Using terpenoid data

Summary Twenty-four populations ofJuniperus ashei were sampled throughout the range of this taxon and the terpenoids of the foliage were analyzed by gas/liquid chromatography. Population differentiation was investigated by analysis of variance and numerical taxonomy. Three south Texas and one Mexican population clustered together with the rest of the taxon appearing fairly uniform. No evidence was found of hybridization or introgression with other taxa. Disjunct populations in Oklahoma and the Ozarks, which have been genetically isolated from the central population for thousands of years, showed no signs of differentiation nor genetic drift. The present pattern of distribution probably dates from the Pleistocene. The south Texas and Mexican populations appear to be the primitive elements of the species. Populational differences have apparently been maintained in adjacent populations in spite of seemingly large gene flow and conversely, chemical uniformity is being maintained in many disjunct populations where there is little or no gene flow.     

How many species are in the genus Batrachuperus? A phylogeographical analysis of the stream salamanders (family Hynobiidae) from southwestern China

Phylogeographical analysis of DNA sequence data has been routinely used to test species boundaries using the monophyly criterion; however, a complementary criterion, reproductive isolation, is often ignored. We used a combination of phylogenetic and population genetic approaches to determine species boundaries among stream salamanders in the genus Batrachuperus . First, cytochrome b sequence data from 174 Batrachuperus individuals, sampled from 78 populations, were used to reconstruct historical relationships within the genus. Second, allozyme data for 14 presumptive nuclear loci, from 463 individuals sampled from 60 populations, were collected and analysed to assess population similarity or disparity, as well as potential reproductive isolation. The DNA sequence data grouped all populations into seven major monophyletic groups, and the allozyme data provided evidence for reproductive isolation among four of the seven groups, thereby supporting the species status of these groups. The allozyme data suggested that two of the other groups share the same gene pool, and therefore belong to a single species. Finally, the allozyme data revealed two reproductively isolated units within the seventh group, which we suggest represents a case of 'budding speciation' based on the DNA gene tree. In total, seven species of the genus Batrachuperus were defined, two of which were previously unknown. The phylogeographical analysis also revealed that vicariance events might have dominated the evolutionary history of this group, but the speciation events might precede the formation of the existing mountain topology. This study demonstrates the importance of including frequency data from multiple nuclear gene loci in determining species boundaries.     

Variability of allozyme and cpSSR markers in the populations of Siberian spruce

The variability of 21 allozyme and three microsatellite loci of chloroplast DNA (cpDNA) was studied in the populations of Siberian spruce (Picea obovata Ledeb.) from Irkutsk oblast, Magadan oblast, Buryatia, and Mongolia. It was demonstrated that the highest level of genetic diversity among the examined populations at both allozyme and microsatellite loci was observed in the Tulyushka population from Irkutsk oblast. The lowest level of genetic diversity was observed in marginal isolated populations of Bogd Uul and Magadan. In the relict spruce population from Olkhon Island, differing from the other populations in the lowest allelic diversity of both types of markers, no expected decline of expected heterozygosity and haplotype diversity was observed. In this population, the variability parameters mentioned were close to the population mean. The obtained intrapopulation and intraspecific variability parameters of allozyme and microsatellite loci of chloroplast DNA and the data on the population differentiation at these loci indicate that the given markers can be used for the analysis of the population structure of Siberian spruce.     

Deeply divergent lineages of the widespread New Zealand amphipod Paracalliope fluviatilis revealed using allozyme and mitochondrial DNA analyses

1. We evaluated the population genetic structure of the common New Zealand amphipod Paracalliope fluviatilis using eight allozyme loci, and the mitochondrial cytochrome oxidase c subunit I (COI) gene locus. Morphological analyses were also conducted to evaluate any phenotypic differences. Individuals belonging to P. fluviatilis were collected from a total of 14 freshwater fluvial habitats on the North and South Islands, New Zealand. 2. We found evidence for strong genetic differentiation among locations (Wright's F_ST > 0.25), and fixed differences (non‐shared alleles) at two of the eight allozyme loci indicating the possibility of previously unknown species. Analysis of a 545‐bp fragment of the COI locus was mostly congruent with the allozyme data and revealed the same deeply divergent lineages (sequence divergences up to 26%). 3. Clear genetic breaks were identified between North Island and South Island populations. North Island populations separated by <100 km also showed genetic differences between east and west draining watersheds (sequence divergence >12%). Accordingly, present‐day dispersal among hydrologically isolated habitats appears minimal for this taxon. 4. Although population differences were clearly shown by allozyme and mtDNA analyses, individuals were morphologically indistinguishable. This suggests that, as in North American and European taxa (e.g. Hyalella and Gammarus), morphological conservatism may be prevalent among New Zealand's freshwater amphipods. We conclude that molecular techniques, particularly the COI gene locus, may be powerful tools for resolving species that show no distinctive morphological differences.     

Genetic and demographic dynamics of small populations of Silene latifolia

Small local populations of Silene alba, a short-lived herbaceous plant, were sampled in 1994 and again in 1999. Sampling included estimates of population size and genetic diversity, as measured at six polymorphic allozyme loci. When averaged across populations, there was very little change between samples (about three generations) in population size, measures of within-population genetic diversity such as number of alleles or expected heterozygosity, or in the apportionment of genetic diversity within and among populations as measured by F(st). However, individual populations changed considerably, both in terms of numbers of individuals and genetic composition. Some populations doubled in size between samples, while others shrank by more than 75%. Similarly, expected heterozygosity and allele number increased by more than two-fold in individual populations and decreased by more than three-fold in others. When population-specific change in number and change in measures of genetic diversity were considered together, significant positive correlations were found between the demographic and genetic variables. It is speculated that some populations were released from the demographic consequences of inbreeding depression by gene flow.