Protein polymorphism in the fresh water snail Semisulcospira libertina

To evaluate genetic variability in 19 population samples of the fresh water snail Semisulcospira libertina, 10 enzymes coded for by 13 presumptive gene loci were examined by starch gel electrophoresis. The mean proportion of polymorphic loci and the mean heterozygosity value estimated for the 19 samples were 0.199 and 0.063, respectively. The mean F statistics of Wright (1943) was estimated over the four polymorphic loci (PGM, 6-PGD, MPI and PGI) for the snail populations to be 0.3615.     

Estimating the Gene Pool Condition in Natural Populations of Invertebrates in the Fragmented Landscape of Moscow and Moscow Region with Special Reference to Bush Snail Bradybaena fruticum Mull.

Using bush snail Bradybaena fruticum Mull (20 populations) as a model, we were the first in Russia and in the world to develop a system of urban ecological genetic monitoring of the gene pool of an invertebrate species. The results of isozyme polymorphism studies in bush snail populations showed a dramatic (up to 70%) reduction in genetic diversity in small isolates from the urbanized environment as compared to large natural populations. In urban populations, genetic diversity parameters were demonstrated to be lower than in natural ones: the mean heterozygosity per locus was reduced up to 0.08 (0.15–0.20 in natural populations); the mean allele number, to 1.9 (2.7 in natural populations); and the number of polymorphic loci, to four, i.e., 2.2-fold (nine in natural populations). In Moscow region, the number of polymorphic loci also decreased to five in the population subjected to anthropogenic pressure. The changes in the population gene pool (as shown by the number of polymorphic loci) were different in Moscow and Moscow region. The percentage of populations with the number of polymorphic loci as low as four to six was 76.9 in Moscow and 23.1% in Moscow region. The gene pool quality of 80% of the urban snail populations was estimated as unsatisfactory, and in half of them, as critical. The main reason for these changes seems to be genetic drift accompanied by inbreeding, caused by fragmentation of the range and reduction in the abundance of populations of the species, due to the anthropogenic pressure. The results of the study were employed in the program of the Moscow government for restoring the gene pools of endangered animals species on the preserved territories of the city.     

Estimating the gene pool condition in natural populations of invertebrates in the fragmented landscape of Moscow and Moscow district with special reference to shrub snail Bradybaena fruticum Müll

Using shrub snail Bradybaena fruticum Müll (20 populations) as a model, we were the first in Russia and in the world to develop a system of urban ecological genetic monitoring of the gene pool of an invertebrate species. The results of isozyme polymorphism studies in shrub snail populations showed a dramatic (up to 70%) reduction in genetic diversity in small isolates from the urbanized environment as compared to large natural populations. In urban populations, genetic diversity parameters were demonstrated to be lower than in natural ones: the mean heterozygosity per locus was reduced up to 0.08 (0.15-0.20 in natural populations); the mean allele number, to 1.9 (2.7 in natural populations); and the number of polymorphic loci, to four, i.e., 2.2-fold (nine in natural populations). In Moscow district, the number of polymorphic loci also decreased to five in the population subjected to anthropogenic pressure. The changes in the population gene pool (as shown by the number of polymorphic loci) were different in Moscow and Moscow district. The percentage of populations with the number of polymorphic loci as low as four to six was 76.9 in Moscow and 23.1% in Moscow district. The gene pool quality of 80% of the urban snail populations was estimated as unsatisfactory, and in half of them, as critical. The main reason for these changes seems to be genetic drift accompanied by inbreeding, caused by fragmentation of the range and reduction in the abundance of populations of the species, due to the anthropogenic pressure. The results of the study were employed in the program of the Moscow government for restoring the gene pools of endangered animals species on the preserved territories of the city.     

Development of 18 microsatellite loci for the freshwater snail Bellamya aeruginosa (Mollusca, Gastropoda)

Although it is a major freshwater gastropod species, genetic diversity of Bellamya aeruginosa was completely unknown. Eighteen microsatellite loci were isolated and characterized from (AC)(15)-enriched genomic libraries of the freshwater snail B. aeruginosa. Most of the 18 loci were successfully amplified and high polymorphic information content values were found, ranging from 0.244 to 0.792 (mean 0.541). The number of alleles per locus ranged from 5 to 13 (mean 8.8), the expected heterozygosity varied from 0.347 to 0.950 (mean 0.815) and the observed heterozygosity varied from 0.087 to 0.782 (mean 0.431). Eight loci showed significant deviation from Hardy-Weinberg equilibrium after Bonferroni's correction and no significant genotypic linkage disequilibrium was detected between most locus pairs, except for TXH79-TXH97 and TXH113-TXH121. These 18 polymorphic microsatellite loci should be useful for population genetics analysis and species identification of Bellamya.     

Characterization of eight microsatellite loci in the Galápagos endemic land snail Bulimulus reibischi, and their cross-species amplification

Variation in and amplification conditions for eight polymorphic microsatellite loci initially identified from Bulimulus akamatus, a pulmonate land snail from Galápagos, are described. Intraspecific polymorphism and heterozygosity of the eight markers were studied in 19 populations of Bulimulus reibischi, a closely related species of B. akamatus. Furthermore, the eight loci were also cross-amplified in six other closely related bulimulid species. The number of alleles across populations of B. reibischi at six loci is moderate (three to 10), but considerable for two other loci (19 and 20). There is no strong evidence for linkage among any of the loci examined.     

Microsatellite loci for the Chinese bamboo rat Rhizomus sinensis

We describe 19 polymorphic microsatellite loci for the bamboo rat Rhizomus sinensis. When tested with 20 samples from a single population, these loci exhibited a mean of 4.5 alleles per locus and a mean expected heterozygosity of 0.612. All loci were in Hardy-Weinberg equilibrium and no evidence for linkage disequilibrium was detected between any loci. These loci will be useful for studying population genetic diversity and differentiation in the Chinese bamboo rat.     

Population genetics of Biomphalaria straminea in Hong Kong. A neotropical schistosome-transmitting snail recently introduced into China

Since its introduction in the early 1970s Biomphalaria straminea (Gastropoda: Planorbidae) has spread rapidly and is locally the most abundant fresh water snail in Hong Kong. Studies of 19 electrophoretically detected loci in four populations show that the colonists retain high levels of variability (P = 0.26, H = 0.056 - 0.097), comparable with those found in autochthonous samples of related species. Genotype frequencies at the five polymorphic loci, and a comparison of maternal and progeny genotypes of individual field-collected snails, revealed no evidence for self-fertilization in these functional hermaphrodites. F statistics indicated minimal genetic structuring, presumably because of outcrossing and recency of origin of the populations. Geographic distribution of various alleles and their frequencies suggest that two southern populations were derived from the original colonists by dispersal but that a northern population represents a second introduction in about 1982. This interpretation (based on genetics) is consistent with the known history of the various populations. The Asian populations of this South American snail are interpreted as being in the "flush" phase of the colonization process. Finally, the probability of the secondary spread of this snail from Hong Kong, and the probability of its parasite, the human blood fluke Schistosoma mansoni, being introduced to Asia are discussed.     

Isolation and characterization of 20 polynucleotide microsatellite markers in a vulnerable Korean snail, <Emphasis Type="Italic">Ellobium chinense,</Emphasis> using 454 pyrosequencing

A small and air-breathing snail, Ellobium chinense (Ellobiidae), is a vulnerable species by International Union for Conservation of Nature (IUCN). To protect and manage habitat and population of E. chinense, microsatellite markers were developed using 454 pyrosequencing and 20 polymorphic microsatellite markers were identified. A total of 146,704 sequences containing a minimum of four repeat motifs (mean, 631 base pairs) were identified from 499,505 reads. Among 80 loci containing more than nine repeat units, 34 primer sets (42.5 %) produced strong PCR products, of which 20 were polymorphic among 48 samples of E. chinense. All loci exhibited high genetic variability, with an average of 18.9 alleles per locus, and the mean observed and expected heterozygosities were 0.65 and 0.90, respectively. In addition, cross-amplification was tested for all 20 loci in the same family species, Melampus sincaporensis. None of the primer pairs resulted in effective amplification, which might be due to their high mutation rates. Our work demonstrated the utility of next-generation 454 sequencing as a method for the rapid and cost-effective identification of microsatellites. The high degree of polymorphism exhibited by the 20 newly developed microsatellites will be useful in future conservation genetic studies of this species.     

Genetic diversity and population structure of Yucca filamentosa (Agavaceae)

Using 19 allozyme loci we studied genetic diversity in 18 populations of Yucca filamentosa (Agavaceae) from the southeastern United States. Of the 19 loci surveyed, 17 (89.5%) were polymorphic in at least one of the populations sampled. There was considerable variation among populations in the percentage of polymorphic loci (range = 31.6-84.2%, mean = 67.6%). Similar heterogeneity among populations was observed for mean number of alleles per polymorphic locus (range = 2.0-3.0; mean = 2.48) and mean expected heterozygosity (range = 0.113-0.288; mean = 0.213). On average, 83% of the total genetic diversity was found within populations. Duplications of three allozyme loci were detected in several populations. The life-history characteristics of Y. filamentosa (a long-lived, semiwoody, predominantly outcrossing monocot with a large geographical range) may contribute to the maintenance of such high levels of genetic diversity. These results contradict expectations of the genetic structure of Y. filamentosa based on observations of the dispersal and pollination behavior of its sole pollinator, Tegeticula yuccasella, the yucca moth.     

Eight polymorphic blood protein systems in Arab horses from Turkey]

Analysis of the blood protein system was used to study the genetic composition of Arabian horses. Biochemical markers of eight polymorphic loci (Tf, Al, Es, AlB, Gc, Hb, PGD, and PGM) were electrophoretically identified in blood samples. A total of 43 phenotypes were identified for these polymorphic systems. The Tf, Hb, and Es loci appeared to be more polymorphic than the other loci studied. Statistically significant differences between the observed and expected genotypic frequencies were found for the PGD and PGM loci (P < 0.05 and P < 0.01, respectively). Individual allele frequencies, observed and expected phenotype frequencies, and the average heterozygosity were estimated for each polymorphic locus.     

Lack of molluscan host diversity and the transmission of an emerging parasitic disease in Bolivia

Fasciolosis is a re-emerging parasitic disease that affects an increasing number of people in developing countries. The most severe endemic affects the Bolivian Altiplano, where the liver fluke (Fasciola hepatica) and its hermaphroditic snail host, Lymnaea truncatula, have been introduced from Europe. To achieve a better understanding of the epidemiological situation and the consequences of the colonization event of this invasive species, genetic analysis of Bolivian snail populations was needed. Here we compare the genetic diversity and population structure of snail samples from the Bolivian Altiplano with samples from the Old World at six polymorphic microsatellite loci. Whereas some variability exists in the snail populations from the Old World, we observe only a single genotype of L. truncatula in the Bolivian Altiplano. We discuss the possible explanations for such a reduction in genetic variability, and, given the high natural parasitism pressures exerted on the snail populations, we discuss the relevance of this result for host-parasite interactions.     

Simultaneous estimation of all the parameters of a stepwise mutation model.

Minisatellite and microsatellite are short tandemly repetitive sequences dispersed in eukaryotic genomes, many of which are highly polymorphic due to copy number variation of the repeats. Because mutation changes copy numbers of the repeat sequences in a generalized stepwise fashion, stepwise mutation models are widely used for studying the dynamics of these loci. We propose a minimum chi-square (MCS) method for simultaneous estimation of all the parameters in a stepwise mutation model and the ancestral allelic type of a sample. The MCS estimator requires knowing the mean number of alleles of a certain size in a sample, which can be estimated using Monte Carlo samples generated by a coalescent algorithm. The method is applied to samples of seven (CA)n repeat loci from eight human populations and one chimpanzee population. The estimated values of parameters suggest that there is a general tendency for microsatellite alleles to expand in size, because (1) each mutation has a slight tendency to cause size increase and (2) the mean size increase is larger than the mean size decrease for a mutation. Our estimates also suggest that most of these CA-repeat loci evolve according to multistep mutation models rather than single-step mutation models. We also introduced several quantities for measuring the quality of the estimation of ancestral allelic type, and it appears that the majority of the estimated ancestral allelic types are reasonably accurate. Implications of our analysis and potential extensions of the method are discussed.SINCE the discovery that a large number of loci with tandemly repeated sequences in human and many eukaryote species are highly polymorphic because of copy number variation of the repeats in different individuals (Jeffreys 1985; Litt and Luty 1989; Weber and May 1989), allele size data from such loci are rapidly becoming the dominant source of genetic markers for genome mapping, forensic testing, and population studies. Loci with repeat sequences longer than 5 bp are generally referred to as minisatellite or variable number tandem repeat loci, and those with repeat sequences between 2 to 5 bp are referred to as microsatellite or short tandem repeat loci (Tautz 1993). Because mutations change the copy number of such loci in a stepwise fashion, rapid accumulation of population samples from minisatellite and microsatellite loci has resurrected the interest of the stepwise mutation model (SMM), which was popular in the 1970s.     

Low genetic differentiation among populations ofArabis serrata (Brassicaceae) along an altitudinal gradient

We investigated the extent of genetic differentiation among populations of fujihatazao,Arabis serrata along an altitudinal gradient at Mt. Fuji in Shizuoka Prefecture. This species is a perennial plant, widely distributed in Japan forming small isolated populations. However, at Mt. Fuji, this species constitutes a large population distributed from 1440 to 2400 m altitude. A total of 411 individuals were sampled from ten subpopulations. Eighteen loci were detected on eleven enzyme systems. Eleven loci were monomorphic and seven loci were polymorphic with a mean of 2.11 alleles per loci. Nei's genetic distance (mean 0.01) and genetic identity (mean 0.968) were very similar among populations indicating a low genetic differentiation. The total genetic diversity (H _T ) estimated for the polymorphic loci was, in average, 0.396. The mean gene differentiation (G_ST=0.091) was very low. Gene frequency of seven polymorphic loci was analyzed by spatial autocorrelation methods based on Moran's indexes. Only Pgi-3 exhibited a significant negative autocorrelation (−0.160;P<0.05); other loci values ranged from −0.134 to 0.027. Gene flow estimated by indirect methods varied between genes but most of the values were high (meanNm=20.8) suggesting that subpopulations at different altitudes are probably connected. Despite plants at different altitudes present different ecological traits (e.g., differences in phenology, growth and reproductive traits), subpopulations ofA. serrata are still low differentiated, at least for the loci studied. This may be explained by the recent origin of some habitats (e.g., second crater and surrounded areas) in this locality.     

ALLOZYME VARIATION AMONG POPULATIONS OF BIOMPHALARIA PFEIFFERI (KRAUSS, 1848) (GASTROPODA: PLANORBIDAE) IN CAMEROON

Allozyme electrophoresis was used to study genetic diversityamong the freshwater, hermaphroditic snail Biomphalaria pfeifferiin Cameroon. Four of 19 loci studied were polymorphic. The allozymesfor two loci, aspartate aminotransferase-1 (AAT-1) and isocitratedehydrogenase (IDH), showed distribution patterns related toclimatic zones. AAT-1¹⁰⁰ and IDH¹⁰⁰ occurred predominantly inthe Tropical Climatic Zone, located in the northern half ofthe country. AAT-1¹⁴⁰ and IDH⁹⁰ were common in the EquatorialZone. Intrapopulation variations occurred in 5 of 19 populationsampled. Only one population, polymorphic for AAT-1 locus, waspanmictic. The other 4 populations were not in Hardy-Weinbergequilibrium. The deficiency of heterozygotes in those populationsis unusual for a member of the genus Biomphalaria and may bedue to a predominance of self-fertilization. Other explanationsinclude ecological factors or the presence of segregated sub-populationsthat do not outcross. This latter hypothesis is supported bythe total absence of heterozygotes for PGM alleles. (Received 24 August 1989; accepted 14 September 1989)     

Algebraic regularities of the ratio of heterozygosity with a mean and variance of quantitative character

The relationships of heterozygosity with the mean and variance of quantitative character were considered under neutrality, additivity and overdominance of polymorphic loci. Attention was drawn to dependence of the patterns of relationships on the number of polymorphic loci (which varied from 1 to 10) and on the type of polymorphic loci, both homogeneous (polymorphic loci are of the same type) and heterogeneous (polymorphic loci are of the two types) samples of 10 polymorphic loci and their combination. It is shown that increase in the number of polymorphic loci is accompanied with extension of the limits of corresponding relations, whereas the patterns of these relations depend on the type of connection of separate polymorphic locus with the quantitative character and on the ratio of different loci in the set of polymorphic loci. It is assumed that the relationship of heterozygosity with quantitative characters, displayed in the number of experimental works, may contain a component mediated by similar statistical effects. It is inferred that the discrepancy between different authors' experimental data on existence or lack of some relationships between multiplicative heterozygosity and morphological variability of quantitative characters can be explained by different types of relations of polymorphic loci to quantitative characters encountered in their works.     

Polymorphic microsatellite loci for the trematode Diplostomum pseudospathaceum

We present primers for five polymorphic microsatellite loci in the eye fluke Diplostomum pseudospathaceum (Trematoda), a widely distributed parasite with a complex life cycle used as a model for parasitology and fish immunology. The loci were identified using a GA/CT‐enriched genomic library by subtractive hybridization with magnetic particles. All five loci were highly polymorphic, displaying 17 to 61 alleles and heterozygosities ranging from 0.53 to 0.92. We isolated populations of parasites within the first (snail) and second (fish) intermediate host and found small but significant genetic differentiation (F_ST = 0.012) between the two life stages of the parasite.     

Ten polymorphic microsatellite loci identified from a small insert genomic library for Peronospora tabacina

Ten polymorphic microsatellite loci for the obligate biotrophic, oomycete pathogen of tobacco, Peronospora tabacina, were identified from a small insert genomic library enriched for GT motifs. Eighty-five percent of the 162 loci identified were composed of dinucleotide repeats, whereas only 4% and 11% were tri-and tetra-nucleotide repeats respectively. About 82% of all the microsatellites were perfect and within the library; only about 7% of the loci were duplicated. Primers were designed for 63 loci; 10 loci were polymorphic, 19 were monomorphic and 34 either failed to amplify or produced ambiguous/inconsistent results. The 10 polymorphic loci were characterized with 44 isolates of P. tabacina collected from tobacco plants growing in Europe, the Near East and North and South America. The number of alleles per locus was either three or four with a mean of 3.2, and the mean number of genotypes per locus was 3.6. Observed heterozygosity was 0.32-0.95, whereas expected heterozygosity was 0.44-0.69 for these loci. All loci except PT054 did not conform to the Hardy-Weinberg distribution. Polymorphic information content (PIC) for the loci was 0.35-0.69 with a mean of 0.50. These microsatellite loci provide a set of markers sufficient to perform genetic diversity and population studies of P. tabacina, and possibly other species of Peronospora.     

Characterization of microsatellite loci for the littorine snail Bembicium vittatum

We describe the isolation and development of 17 polymorphic microsatellite loci for the intertidal snail Bembicium vittatum (Gastropoda: Littorinidae). The loci were tested in 46 individuals from a single population situated near the centre of the species distribution. No evidence of linkage disequilibrium was detected between any pair of loci. However, two loci showed significant departures from Hardy-Weinberg expectations. The number of alleles per locus ranged from two to 15.     

Isolation and characterization of microsatellite loci from the endangered New Zealand takahe (Gruiformes; Rallidae; Porphyrio hochstetteri)

Nineteen polymorphic microsatellite loci were characterized from the endangered takahe (Porphyrio hochstetteri). Like many of New Zealand's other native avian species, levels of polymorphism were low, with variation detected at only 19 of 110 (17.3%) loci, and most polymorphic loci (78.9%) were diallelic (mean number of alleles = 2.3). Despite these low levels of variation, the microsatellites developed here will be useful for parentage assignment for confirming pedigrees, and investigating relationships between genetic variation, pedigree‐based inbreeding and reproductive success in this highly endangered species.