Effect of isolation on the genetic characteristics of populations in charrs of the genus Salvelinus

To study the effect of isolation on the genetic variation of mDNA, Salvelinus malma krascheninnikovi and S. malma malma nonanadromous populations from different model ecosystems were examined by RT-PCR. The haplotype and nucleotide diversities of mtDNA were significantly decreased in three isolated populations as a result of random gene drift. The genealogy of mtDNA haplotypes was reconstructed. The formation of the modem structure of the isolated populations is discussed in terms of phylogeography.     

Fish growth hormone genes: Divergence of intron sequence in charrs of Salvelinus genus

Sequences of the two large introns (C and D) from two paralogous growth hormone genes, GH1 and GH2, were compared in eight charr species of the Salvelinus genus (Osteichthes, Salmonidae). It was demonstrated that the rates of intron divergence in these two genes were remarkably different. Introns in the GH1 gene appeared to be more conservative, while the rate of intron variations was considerably higher in the GH2 gene. These data suggest that noncoding regions of nuclear genes under the selective pressure. The lower congruence of phylogenetic scheme constructed based on an analysis of the GH1 introns compared to that based on the GH2 data, as well as with the traditional views on the evolution of charr species, also favors the supposition on differences in the forces and directions of the selective pressure on the introns.     

On the origin of charrs of the genus Salvelinus of the Kronotskoe Lake and their relationships with other charr populations of the Kamchatka peninsula

To reveal genetic differentiation and origin of sympatric Lake Kronotskoe charr morphs, we sequenced a fragment of control region (558-bp) and Cytochrome B gene (1015-bp) (combined length 1573-bp) in 232 specimens from the lake and, as an outgroup, 57 specimens from the Kronotskaya River below water-falls (anadromous malma) and 77 specimens from other large water bodies from the Kamchatka. A total of 52 nucleotide positions were polymorphic, and these defined 67 haplotypes. Our data does not allow to estimate genetic differentiation among different lake-dwelling morphs, but strongly supports the monophyletic origin of all morphs within the lake. To estimate genetic differentiation and population structure, an extensive study of microsatellite variation has to be conducted.     

Genetic divergence of sympatric charrs of the genus Salvelinus from Nachikinskoe Lake (Kamchatka)

We studied genetic differentiation of two charr species, Dolly Varden Salvelinus malma malma Walbaum and resident lacustrine charr Salvelinus sp., which sympatrically inhabit Nachikinskoe Lake (the Bol'shaya River basin) in southwestern Kamchatka Peninsula. Using restriction analysis (RFLP), three mitochondrial DNA fragments (ND1/ND2, ND5/ND6, and Cytb/D loop) amplified in polymerase chain reaction (PCR) were compared. The divergence of the mtDNA sequences between Salvelinus sp. and S. malma malma was 2.8%; Salvelinus sp. and S. taranetzi, 0.36%; Salvelinus sp. and S. krogiusae, 0.21%; Salvelinus sp. and S. alpinus, 3.0%. These results point to reproductive isolation of charrs in Nachikinskoe Lake and support the earlier suggestion on a close relationship between Salvelinus sp., S. taranetzi, and S. krogiusae.     

Comparative ontogeny of photobehavioural responses of charrs (Salvelinus species)

Synopsis The development of photobehavioural responses in brook (Salvelinus fontinalis) and lake (S. namaycush) charr was studied by monitoring the intrasubstrate movements and concurrent photoresponse behaviour of incubated embryos and alevins. Photoresponse behaviour of both F-1 hybrids of the parent species was also recorded. All embryos initially moved downward in the substrate, however brook charr descended farther and faster into the substrate than did lake charr. Photoresponse tests demonstrated a similar pattern of photoresponse transformation from a photonegative to a photopositive state in both species. However, photoresponse reversal was faster, more extensive and occurred later in brook charr than in lake charr. Patterns of photoresponse change in F-1 hybrids were intermediate between those of the parent species. Photoresponse shifts preceded the onset of alevin emergence in both species. occurring when differential development of various morphological characters existed. Developmental states of characters were synchronously maximal towards the end of alevin emergence. Intermediate measures of morphological development were observed for F-1 hybrids. Possible functions and mechanisms of photoresponse transitions are discussed in relation to ecological differences between the species.     

Trophic-based diversification in benthivorous charrs (Salvelinus) dwelling littoral zones of Northern lakes

Charrs of the genus Salvelinus form distinct trophic morphs living in sympatry in numerous postglacial lakes. Here we demonstrate that charrs can diversify into amphipod foraging specialists and sedentary macrobenthos consumers in the shallow-water ecosystems. This pattern was revealed in three out of six lakes under exploration supported by differences in stomach content, trophic-transmitted parasite, and stable isotope ratio analyzes. The body shape and growth rate comparison indicates that this kind of trophic-based diversification emerges at a juvenile stage and is maintained throughout the whole life. The restriction in gene flow found between the morphs allows to propose the possibility for the hereditable-based specialization to evolve. We found that those diversification phenomena are possible only in the lakes situated in vicinity of the ocean coastline, while no evidence of this split was found for inland mountain lakes. We suggest that the trophic-based diversification in the littoral ecosystems is accounted for the heterogeneity in the ecological conditions and food resources’ distribution linked to coastal wind action. This phenomenon was previously reported for the charr in Lake Fjellfrosvatn, Scandinavia, so it seems to be some universal yet poorly described kind of disruptive selection pressure for northern latitude fishes.

     

Comparative restriction enzyme analysis of mitochondrial DNA in several populations of lake resident chars of the genus Salvelinus

Restriction enzyme analysis was employed in studying the mitochondrial DNA (mtDNA) ATPase6/ND4L region in several Northeast Asian populations of resident lake char of the genus Salvelinus. On evidence of mitotypes, genetic similarity was assumed for populations of neiva (Ueginskoe Lake), lake resident char from the northern coast of the Sea of Okhotsk (Mak-Mak Lake and Elekchanskie lakes), and dolly varden. Mitotype AAAA proved to be common for these populations. Lake char populations of the Juliet and Maxi lakes (the basin of the Kolyma river) had mitotype DBAA, which is similar to mitotype DBAB observed earlier in Taranetz char S. taranetzi from Chukotka. The divergence between mitotypes AAA and DBAA was estimated at 0.3%. Different origins were assumed for the lake resident char populations from the basins of the Sea of Okhotsk and of the Kolyma River, the former originating in the Pacific and the latter, in the Arctic basins.     

A metric based on Malecot's parameters of isolation by distance as a characteristics of genetic similarity of populations

A new metric based on Malecot's parameters of isolation by distance is proposed for estimation of genetic similarity between populations. This metric is in good agreement with the angular metric used for estimation of interpopulation genetic distances. It is suggested to term the new metric Malecot's metric.     

The genetic isolation between some populations of Proasellus coxalis

We tested the reroductive compatibility existing between four geographically different populations of Proaselis coxalis (Crustacea Isopoda) collected in the river Sarno (near Naples) and on three Sicilian sites: San Domenico; Villa Grazia di Carini and Enna. By means of laboratory hybridization experiments (“no-choice” method) we investigated and characterized the reproductive isolation established between these populations under allopatric conditions. The populations San Domenico and Enna are reproductively isolated from Villa Grazia di Carini and Sarno, so that they may be considered as belonging to different species. The mechanism of reproductive isolation are of postzygotic nature only: embronic death, hbrid inviability and sterility of the surviving hybrids. These results agree with tie theory of aioatric speciation, according to which in the first phase of speciation only post-zygotic mechanisms occur as an accidental product of genetic divergence.     

The impact of stocking on the genetic integrity of Arctic charr (Salvelinus) populations from the Alpine region

There is a long tradition of artificially stocking lakes and rivers with fish in the hope to increase the quality and amount of fish that can be harvested. The animals used for stocking often originate in distant hatcheries or hatcheries that breed fish from remote regions. This stocking practice could have effects on the genetic integrity of resident populations. We have analysed here a case of the influence of stocking on Alpine populations of the Arctic charr (usually included into Salvelinus alpinus, but revised to Salvelinus umbla Kottelat 1997 ) within a unique geographical and historical setting. The Königssee in the Bavarian Alps (Berchtesgaden) was heavily stocked several times during the last century. However, a sample of the ancestral Königssee population still exists in the Grünsee, which lies close to Königssee, but 1000 m higher. To trace the influence of stocking in Königssee we have analysed more than 300 individuals from 10 lake populations, including the source populations of the fish used for stocking. From these we have sequenced a part of the mitochodrial control region and have typed them at six microsatellite loci. The differential distribution of haplotypes, as well as assignment tests, show that the influence of stocking on the genetic integrity of the Königssee population has been negligible. However, our data reveal that in another lake included in our study (Starnberger See), the ancestral population was apparently replaced completely by the populations used for stocking. The major difference between the lakes is the relative preservation of ecological integrity. Königssee was ecologically stable in the past, whereas Starnberger See was heavily polluted at one point, with charr approaching extinction. Interestingly, in a lake neighbouring Starnberger See, the Ammersee, which was also subject to strong pollution but not stocked, the ancestral population has recovered. Our data suggest that the practice of artificial stocking should be reconsidered, or at least monitored for effectiveness.     

Spatial isolation and genetic differentiation in naturally fragmented plant populations of the Swiss Alps

Aims The effect of anthropogenic landscape fragmentation on the genetic diversity and adaptive potential of plant populations is a major issue in conservation biology. However, little is known about the partitioning of genetic diversity in alpine species, which occur in naturally fragmented habitats. Here, we investigate molecular patterns of three alpine plants (Epilobium fleischeri, Geum reptans and Campanula thyrsoides) across Switzerland and ask whether spatial isolation has led to high levels of population differentiation, increasing over distance, and a decrease of within-population variability. We further hypothesize that the contrasting potential for long-distance dispersal (LDD) of seed in these species will considerably influence and explain diversity partitioning.Methods For each study species, we sampled 20–23 individuals from each of 20–32 populations across entire Switzerland. We applied Random Amplified Polymorphic Dimorphism markers to assess genetic diversity within (Nei's expected heterozygosity, H e; percentage of polymorphic bands, P p) and among (analysis of molecular variance, Φ st) populations and correlated population size and altitude with within-population diversity. Spatial patterns of genetic relatedness were investigated using Mantel tests and standardized major axis regression as well as unweighted pair group method with arithmetic mean cluster analyses and Monmonier's algorithm. To avoid known biases, we standardized the numbers of populations, individuals and markers using multiple random reductions. We modelled LDD with a high alpine wind data set using the terminal velocity and height of seed release as key parameters. Additionally, we assessed a number of important life-history traits and factors that potentially influence genetic diversity partitioning (e.g. breeding system, longevity and population size).Important findings For all three species, we found a significant isolation-by-distance relationship but only a moderately high differentiation among populations (Φ st : 22.7, 14.8 and 16.8%, for E. fleischeri, G. reptans and C. thyrsoides, respectively). Within-population diversity (H e : 0.19–0.21, P p : 62–75%) was not reduced in comparison to known results from lowland species and even small populations with <50 reproductive individuals contained high levels of genetic diversity. We further found no indication that a high long-distance seed dispersal potential enhances genetic connectivity among populations. Gene flow seems to have a strong stochastic component causing large dissimilarity between population pairs irrespective of the spatial distance. Our results suggest that other life-history traits, especially the breeding system, may play an important role in genetic diversity partitioning. We conclude that spatial isolation in the alpine environment has a strong influence on population relatedness but that a number of factors can considerably influence the strength of this relationship.     

Effect of mass selection on the within-family genetic variance in finite populations

Summary The adequacy of an expression for the withinfamily genetic variance under pure random drift in an additive infinitesimal model was tested via simulation in populations undergoing mass selection. Two hundred or one thousand unlinked loci with two alleles at initial frequencies of 1/2 were considered. The size of the population was 100 (50 males and 50 females). Full-sib matings were carried out for 15 generations with only one male and one female chosen as parents each generation, either randomly or on an individual phenotypic value. In the unselected population, results obtained from 200 replicates were in agreement with predictions. With mass selection, within-family genetic variance was overpredicted by theory from the 12th and 4th generations for the 1,000 and 200 loci cases, respectively. Taking into account the observed change in gene frequencies in the algorithm led to a much better agreement with observed values. Results for the distribution of gene frequencies and the withinlocus genetic covariance are presented. It is concluded that the expression for the within-family genetic variance derived for pure random drift holds well for mass selection within the limits of an additive infinitesimal model.     

Effect of mutation on genetic differentiation among nonequilibrium populations

The usefulness of GST and similar measures of genetic differentiation has been questioned repeatedly because of their dependence on the amount of heterozygosity within populations, creating problems when comparing degrees of divergence at loci with different mutation rates. Although the effect of mutation on GST is expected to be small in the early phases of divergence, it is unclear for how long after separation from a common ancestral population that GST is largely unaffected by mutation and by the resulting effect on heterozygosity. We address this question through analysis of the recursion equations for gene identity under the infinite allele model of mutation, and derive conditions describing when the effect of mutation on GST can be ignored under mutation-migration-drift equilibrium conditions and during the preceding transition phase. An important result is that during the transition phase GST is not only affected by mutation, but also by the heterozygosity in the base population from which the subpopulations diverged. The effect of mutation on GST is significant from the very start of the divergence process when initial heterozygosity is low, whereas GST is only weakly affected by mutation in the early phases of differentiation when initial heterozygosity is high. Thus, differentiation following a severe bottleneck is strongly dependent on mutation. The standardized measure of differentiation, G'ST, suggested by Hedrick (2005), may be helpful when comparing amounts of divergence at loci with different mutation rates under steady-state conditions, provided that migration is very low. In many other situations the use of G'ST might be misleading, however, and its application should be exercised with caution.     

Inheritance of bluesac disease for hatchery charr of the genus Salvelinus

Synopsis Bluesac disease is one of the major causes of post-hatching embryo mortality in salmonids. The incidence of bluesac is strongly inherited in splake (Salvelinus fontinalis × S. namaycush hybrid) under hatchery conditions. Lake charr, F₂ splake, F₆ splake, and lake charr backcrosses of F₆ splake had incidences of 7%, 23%, 5% and 40% respectively. For the backcrosses, which are of practical interest because they are used for experimental plantings in the Great Lakes and northern Ontario inland lakes, the variation among families in the incidence of bluesac is primarily determined by the splake parent. Hence the incidence of bluesac disease in the progeny of splake and lake chair is considered to be a character of the splake parent. The heritability of this character in the splake is about 0.74. The level of bluesac in the backcrosses can, therefore, be significantly reduced in one generation by selecting as breeders those splake that produce low levels of bluesac in test backcrosses to lake charr.     

Reproductive isolation among cryptic species in the ectomycorrhizal genus Strobilomyces: population-level CAPS marker-based genetic analysis

Among the higher fungi, reproductively isolated cryptic species exist that are morphologically difficult to distinguish owing to a lack of taxonomically useful morphological characters. Mating tests are helpful for detecting reproductive isolation between cryptic species, but are often difficult to perform for higher fungi, especially ectomycorrhizal fungi. In order to identify cryptic species of the ectomycorrhizal genus Strobilomyces more efficiently, lineages were defined based on the nucleotide sequence of two mitochondrial genes. Then the gene flow among lineages was measured using cleaved amplified polymorphic sequences (CAPS) markers designed for single copy nuclear genes. No heterozygosity was observed between different lineages, but within the same lineage heterozygosity was present at the ratio expected given Hardy Weinberg equilibrium. These results show that the mtDNA lineages are separate Mendelian populations, possibly cryptic species that are reproductively isolated from each other.     

Spatial and temporal changes in genetic structure and diversity of isolated white-spotted charr (Salvelinus leucomaenis) populations

Hydrobiologia - In Japan, numerous artificial dams constructed for erosion control or hydroelectric power generation have affected almost all rivers and resulted in isolation and fragmentation of...     

Influence of spatial structure on genetic isolation in Plebejus argus populations (Lepidoptera: Lycaenidae)

Populations of Plebejus argus were sampled in southwest Finland, both on the mainland and on islands, and in and around the Do?ana National Park in southwest Spain. A total of 453 individuals coming from 14 locations were investigated using allozyme electrophoresis on a total of 10 polymorphic allozyme loci. Contrary to earlier studies, all conducted in Britain, our samples showed little differentiation between sampled locations. In Spain, the populations of the Dona?a area showed no differentiation despite being up to 36 km apart; only the population to the south of the Guadalquivir river showed a significant difference to the others. In Finland the population on one island showed marked genetic differentiation from all the others, which showed little or no difference from each other. No isolation-by-distance effect could be detected in either system. We hypothesise that emigration-immigration events are more frequent in the Spanish and Finnish populations than in the British ones. We did, however, find two isolated populations, one in Spain and one in Finland; both were small and geographically isolated and shared evident drift.     

Allopatric divergence, secondary contact, and genetic isolation in wild yeast populations

In plants and animals, new biological species clearly have arisen as a byproduct of genetic divergence in allopatry. However, our understanding of the processes that generate new microbial species remains limited [1] despite the large contribution of microbes to the world's biodiversity. A recent hypothesis claims that microbes lack biogeographical divergence because their population sizes are large and their migration rates are presumably high [2, 3]. In recapitulating the classic microbial-ecology dictum that "everything is everywhere, and the environment selects"[4, 5], this hypothesis casts doubt on whether geographic divergence promotes speciation in microbes. To date, its predictions have been tested primarily with data from eubacteria and archaebacteria [6-8]. However, this hypothesis's most important implication is in sexual eukaryotic microbes, where migration and genetic admixture are specifically predicted to inhibit allopatric divergence and speciation [9]. Here, we use nuclear-sequence data from globally distributed natural populations of the yeast Saccharomyces paradoxus to investigate the role of geography in generating diversity in sexual eukaryotic microbes. We show that these populations have undergone allopatric divergence and then secondary contact without genetic admixture. Our data thus support the occurrence of evolutionary processes necessary for allopatric speciation in sexual microbes.