GENETIC DIVERSITY AND POPULATION STRUCTURE IN CAMELLIA JAPONICA L. (THEACEAE)

Camellia japonica is a widespread and morphologically diverse tree native to parts of Japan and adjacent islands. Starch gel electrophoresis was used to score allelic variation at 20 loci in seeds collected from 60 populations distributed throughout the species range. In comparison with other plant species, the level of genetic diversity within C. japonica populations is very high: 66.2% of loci were polymorphic on average per population, with a mean number of 2.16 alleles per locus; the mean observed and panmictic heterozygosities were 0.230 and 0.265, respectively. Genotypic proportions at most loci in most populations fit Hardy-Weinberg expectations. However, small heterozygote deficiencies were commonly observed (mean population fixation index = 0.129). It is suggested that the most likely cause of the observed deficiencies is population subdivision into genetically divergent subpopulations. The overall level of population differentiation is greater than is typically observed in out-breeders: The mean genetic distance and identity (Nei's D and I) between pairs of populations were 0.073 and 0.930, respectively, and Wright's Fst was 0.144. Differences among populations appeared to be manifested as variation in gene frequencies at many loci rather than variation in allelic composition per se. However, the patterns of variation were not random. Reciprocal clinal variation of gene frequencies was observed for allele pairs at six loci. In addition, principal components analysis revealed that populations tended to genetically cluster into four regions representing the geographic areas Kyushu, Shikoku, western Honshu, and eastern Honshu. There was a significant relationship between genetic and geographic distance (r = 0.61; P < 0.01). Analysis of variance on allozyme frequencies showed that there was approximately four times as much differentiation among populations within regions, as among regions. It is likely that the observed patterns of population relationships result from the balance between genetic drift in small subpopulations and gene flow between them.     

BIOCHEMICAL GENETICS OF MOSQUITOFISH. IV. CHANGES OF ALLELE FREQUENCIES THROUGH TIME AND SPACE

Gene frequency data from samples of Gambusia affinis populations at 76 localities across the Savannah River drainage were used to investigate temporal and spatial patterns in population genetic structure. Localities in the Par Pond system on the Savannah River Plant were sampled in 1971, 1977, and 1979. Allelic frequencies in these populations were generally stable through time, although significant temporal changes were observed among samples from Pond C, an impoundment receiving thermal effluent. Significant spatial heterogeneity in allele frequencies was observed on both microgeographic and regional scales. Populations within the Par Pond system were spatially subdivided at four of the five loci surveyed (mean F_ST = 0.051). Subdivision was even more pronounced when samples from across the Savannah River drainage were compared (mean F_ST = 0.196). A hierarchial analysis of gene diversity (G_ST) demonstrated that most of the genic diversity across the drainage exists as within-subdivision diversity. Even when populations from such contrasting habitats as rivers, creeks, ponds, and reservoirs are compared, an average of only 13% of the total gene diversity was attributed to between-group diversity. Greatest between-group gene diversity was observed when reservoirs were compared with one another. This general pattern of low between-habitat diversity suggests that differential selection pressures are not playing a major role in producing the observed levels of subdivision. In the Par Pond system, neither single locus nor multilocus genetic distances were significantly associated with geographic distance or with its reciprocal. For samples from over the Savannah River drainage, significant correlations between genetic and geographic distance were observed only for the Gpi-2 and Pgm-2 loci. Thus, there was a general lack of concordance between genetic and geographic distances. Spatial autocorrelation demonstrated patterns consistent with Wright's isolation by distance model. Significant positive correlations in allelic frequencies among neighboring populations were observed for five of six alleles; allelic frequencies in more distantly separated populations were typically not correlated.     

THE GENETIC STRUCTURE OF LARGE-LAKE DAPHNIA POPULATIONS

Cyclical parthenogenesis allows study of the genetic and evolutionary characteristics of groups exhibiting both asexual and sexual reproduction. The cladoceran genus Daphnia contains species which vary with respect to the relative incidence of sexual reproduction; pond species tend to undergo sexual reproduction more regularly than species found in large lakes. Previous genetic studies have focused on pond populations, generating expectations about large-lake populations that have not been fully met by recent studies. The present study of the Palearctic species Daphnia galeata further examines the genetic structure of large-lake populations. Nine local populations, from lakes in northern Germany, are examined for genetic variation at seven enzyme loci. Populations exhibit similar allelic arrays and often similar allele frequencies at the five polymorphic loci; values of Nei's genetic distance (D) ranged from 0.002 to 0.239, with a mean of 0.084. F_ST values range from 0.012 to 0.257, and spatial autocorrelation coefficients range from -0.533 to 0.551, for the eight alleles analyzed. With few exceptions, within-population genotypic frequencies were in Hardy-Weinberg equilibrium. There was, however, significant heterogeneity in genotypic frequencies among populations. The number of coexisting clonal groups, as determined by three locus genotypes, is high within populations. Clonal groups are widely distributed among localities. The amount of genetic divergence observed among these large-lake populations is smaller than that previously observed among pond populations and suggests that different processes may be important in determining the genetic structure and subsequent phenotypic divergence of lake versus pond populations.     

Polymorphic microsatellite loci in the sponge Crambe crambe (Porifera: Poecilosclerida) and their variation in two distant populations

Seven polymorphic microsatellite loci were characterized in the marine encrusting sponge Crambe crambe from a partial genomic DNA‐enriched library. Preliminary data on allelic variation of these loci in two distant populations of C. crambe are presented to assess their potential utility as high‐resolution genetic markers for this species. The number of alleles per locus ranged between three and 16 and the distributions of allele frequencies differed considerably between the two populations, indicating a marked genetic differentiation between them. These are the first microsatellite loci reported from any species in the phylum.     

Molecular evidence for historical and recent population size reductions of tiger salamanders (Ambystoma tigrinum) in Yellowstone National Park

Population declines caused by natural and anthropogenic factors can quickly erode genetic diversity in natural populations. In this study, we examined genetic variation within 10 tiger salamander populations across northern Yellowstone National Park in Wyoming and Montana, USA using eight microsatellite loci. We tested for the genetic signature of population decline using heterozygosity excess, shifts in allele frequencies, and low ratios of allelic number to allelic size range (M-ratios). We found different results among the three tests. All 10 populations had low M-ratios, five had shifts in allele frequencies and only two had significant heterozygosity excesses. These results support theoretical expectations of different temporal signatures among bottleneck tests and suggest that both historical fish stocking, recent, sustained drought, and possibly an emerging amphibian disease have contributed to declines in effective population size.     

Microsatellite DNA variability in the populations of muskoxen <Emphasis Type="Italic">Ovibos moschatus</Emphasis> transplanted into the Russian North

The muskoxen populations introduced to the Taimyr Peninsula and Wrangel Island in 1974 to 1975 were examined for sequence variation at seven microsatellite loci. Donor material originated from the populations of Banks Island (Canada) and Eastern Greenland. Relative to the allele frequencies, both introduced populations demonstrated rather strong deviation from the populations of the native range. At the same time, population allelic structures evidenced that they were closer to the Greenland populations. Estimates of genetic diversity at microsatellite loci (expected heterozygosity and the allele number) in the introduced muskoxen were found to be high for populations originating from a small number of founder individuals. In the immigrants, linkage disequilibrium and deviation of the genotype frequencies from the Hardy-Weinberg proportions were observed, which was mainly caused by the deficit of heterozygotes. The same pattern was also typical of native populations and was explained in terms of specific population structure and demographic processes. The latter were manifested as a periodic decline of the effective population size, resulting in the prevailing influence of genetic drift and inbreeding. The consequences of genetic drift were not as dramatic, as could be expected, which may be explained by a high mutation rate of neutral microsatellite loci and fast growth of the new populations.     

Allozyme variation among natural populations of Holopedium gibberum (Crustacea; Cladocera)

• 1 Holopedium gibberum, from twenty lakes in Rhode Island and Maine, were examined for allozyme variation at five loci to determine the pattern and degree of generic variation among sites and the genetic structure within individual lakes.
• 2 There were significant differences in allele frequencies among sites. Most populations were fixed for a particular allele at each locus. Only five lakes had polymorphic populations.
• 3 Polymorphic populations showed significant deviation from expected Hardy-Weinberg genotype frequencies. In each case, there was an excess of homozygotes.
• 4 Two lakes were examined for intra-lake allele frequency differences. In one lake there were no differences. The other lake exhibited significant allele frequency differences between stations at the north and south ends of the lake.
• 5 Populations were examined for the frequency distribution of composite genotypes over three loci. Most populations were dominated by one or two genotypes.
• 6 The results suggest sporadic sexual recruitment and a high degree of genetic isolation among these populations of H. gibberum. In these respects they resemble the permanent pond populations of Daphnia magna examined by Hebert (1974a).

     

Genetic variability in white-tailed deer (Odocoileus virginianus) and its relationship to environmental parameters and herd origin (Cervidae)

Allozyme variation was examined in 1571 white-tailed deer (Odocoileus virginianus) from 29 localities in Tennessee by starch gel electrophoresis. For 11 polymorphic loci, sex-related, age-related and temporal differences were minimal. However, significant spatial hererogeneity was evident in genotypes (contingency table results), allele frequencies (F _ST=0.057) and heterozygosity. Heterozygosity ranged from 16.9% to 26.8% with a mean of 22.9%. The spatial pattern of allele frequencies determined from Rogers' coefficients of genetic similarity indicated associations based on geographic proximity and stocking history. In hierarchial analyses, physiographic regions accounted for more of the total gene diversity than herd origin groups (populations of similar origin) but less than individual populations. For five loci, physiographic regions accounted for more of the gene diversity than populations, suggesting a selection role in the observed genetic variability. Bivariate and canonical correlation analyses revealed significant associations between environmental and genetic variables. Temperature variables and allele frequencies for three loci (alcohol dehydrogenase, alpha-glycerophosphate dehydrogenase, sorbitol dehydrogenase) had the prominent roles in the multivariate association between environmental and genetic variables. Herd origin, gene flow and selection appear to be involved in the gene diversity in deer from Tennesee.     

Variation in MHC genotypes in two populations of house sparrow (Passer domesticus) with different population histories

Small populations are likely to have a low genetic ability for disease resistance due to loss of genetic variation through inbreeding and genetic drift. In vertebrates, the highest genetic diversity of the immune system is located at genes within the major histocompatibility complex (MHC). Interestingly, parasite‐mediated selection is thought to potentially maintain variation at MHC loci even in populations that are monomorphic at other loci. Therefore, general loss of genetic variation in the genome may not necessarily be associated with low variation at MHC loci. We evaluated inter‐ and intrapopulation variation in MHC genotypes between an inbred (Aldra) and a relatively outbred population (Hestmannøy) of house sparrows (Passer domesticus) in a metapopulation at Helgeland, Norway. Genomic (gDNA) and transcribed (cDNA) alleles of functional MHC class I and IIB loci, along with neutral noncoding microsatellite markers, were analyzed to obtain relevant estimates of genetic variation. We found lower allelic richness in microsatellites in the inbred population, but high genetic variation in MHC class I and IIB loci in both populations. This suggests that also the inbred population could be under balancing selection to maintain genetic variation for pathogen resistance.     

Microgeographic structure of Anopheles gambiae in western Kenya based on mtDNA and microsatellite loci

The population genetic structure of the Anopheles gambiae in western Kenya was studied using length variation at five microsatellite loci and sequence variation in a 648-nt mtDNA fragment. Mosquitoes were collected from houses in villages spanning up to 50 km distance, The following questions were answered, (i) Are mosquitoes in a house more related genetically to each other than mosquitoes between houses? (ii) What degree of genetic differentiation occurs on these geographical scales? (iii) How consistent are the results obtained with both types of genetic markers? At the house level, no differentiation was detected by F_ST and R_ST, and the band sharing index test revealed no significant associations of alleles across loci. Likewise, indices of kinship based on mtDNA haplotypes in houses were even lower than in the pooled sample. Therefore, the hypothesis that mosquitoes in a house are more related genetically was rejected. At increasing geographical scales, microsatellite allele distributions were similar among all population samples and no subdivision of the gene pool was detected by F_ST or R_ST. Likewise, estimates of haplotype divergence of mtDNA between populations were not higher than the within population estimates, and mtDNA-based F_ST values were not significantly different from zero. That sequence variation in mtDNA provided matching results with microsatellite loci (while high genetic variation was observed in all loci), suggested that this pattern represents the whole genome. The minimum area associated with a deme of A. gambiae in western Kenya is therefore larger than 50 km in diameter.     

Genetic analysis of song dialect populations in Puget Sound white-crowned sparrows

The relationship between cultural variation and biological variationamong natural populations has been the subject of both theoreticaland empirical study. Zonotrichia leucophrys pugetensis is oneof three subspecies of white-crowned sparrow known to form geographicalsong dialects. We investigated whether these dialects correspondto genetic differences among Z. l. pugetensis populations. Wecompared allele frequencies at four microsatellite loci in malesfrom 11 sites spanning six dialects over the subspecies' rangein Oregon and Washington. Cluster analysis and genotype assignmenttests indicated no tendency for sample sites within dialectareas to be genetically more similar than are sites from differentdialect areas. AMOVA tests revealed high within-site variationand low but significant cross-site and cross-dialect-area variation.Finally, genetic distance between sites was not correlated withdialect differences when the effect of geographic distance wascontrolled statistically. We compare our finding of low geneticdifferentiation among Z. l. pugetensis dialect populations toresults of previous studies on Z. l. nuttalli and Z. l. oriantha.Because genetic structuring appears weaker than cultural (songdialect) structure in this species, we discuss the behavioralmechanisms underlying dialect maintenance in the presence ofapparent gene flow.     

Population genetic structure of mussels from the Baltic Sea

In a macrogeographic survey, the population genetic structure of mussels from various regions of the Baltic Sea, a large semi-enclosed brackish-water basin, was examined with reference toMytilus edulis andM. galloprovincialis samples from the North Sea, Irish coast and southern Portugal. Electrophoretically detectable variation was analysed at 6 polymorphic enzyme loci (Ap, Est-D, Lap-2, Odh, Pgi andPgm). Evidence was provided of a remarkably large amount of biochemical genetic differentiation among ecologically and morphologically divergent mussel populations in the Baltic. Patterns of allele frequencies in low-salinity populations from the area of the Baltic Proper were demonstrated to be widely homogeneous but contrast strongly with those of the western Baltic, the latter resembling populations from marine habitats of the North Sea. Associated with a pronounced salinity gradient, the spatial heterogeneity in gene-pool structure is indicated by steep clines of allele frequency changes in the area of the eastern Danish isles. The adaptive significance of the observed allozymic variation is suggested. From genetic distance estimates, the subdivision of population structure is discussed in relation to the significant amount of differentiation detected withinMytilus populations to date and to the evolutionary time required for the divergence of Baltic mussel populations. The allozymic data provide evidence for the genetic distinctiveness of mussels from the low-salinity areas of the Baltic. Their position at the specific or subspecific level of classification requires further consideration.     

Genetic biogeography of the rare “copper moss,” Mielichhoferia elongata (Bryaceae)

Mielichhoferia elongata, one of the so-called “copper mosses,” has a broad but highly disjunctive geographic distribution and is rare throughout its range. A genetic analysis of 30 populations based on a survey of 21 allozyme loci reveals the following. 1) Total gene diversity at the specific level is high (0.41). 2) Within-population diversity is low, and over 90% of all genetic variation is among rather than within populations (mean G_ST = 0.93). 3) There is little differentiation in allele frequencies between North American and European populations. 4) Populations consist of one to six multilocus genotypes; 13 of the populations appear to consist of a single clone. 5) Colorado populations contain a tremendous reservoir of genetic variation (88% of all alleles found in the species in North America and Europe occur in one or more Colorado populations). 6) Populations in the eastern and western United States, and in Europe, contain subsets of the allelic diversity found in Colorado. The genetic structure of M. elongata suggests repeated dispersal and founding of populations.     

The mode of evolution of molecular markers in populations of house mice under artificial selection for locomotor behavior

A complete understanding of the mode of evolution of molecular markers is important for making inferences about different population genetic parameters, especially because a number of studies have reported patterns of allelic variation at molecular markers that are not in agreement with neutral evolutionary expectations. In the present study, house mice (Mus domesticus) from the fourteenth generation of a selection experiment for increased voluntary wheel-running activity were used to test how selection on a complex behavior affects the distribution of allelic variation by examining patterns of variation at six microsatellite and four allozyme loci. This population had a hierarchical structure that allowed for simultaneous testing of the effects of selection and genetic drift on the distribution of allelic variation by comparing observed patterns of allele frequencies and estimates of genetic divergence at multiple hierarchical levels to expectations under models of neutral evolution. The levels of genetic divergence among replicate lines and between selection groups, estimated from microsatellite data or pooled microsatellite and allozyme data, were not significantly different from expectations under neutral evolution. Furthermore, the pattern of change of allele frequencies between the base population and generation 14 was largely in agreement with expectations under neutral evolution (although the PGM locus exhibited a pattern of change within populations that was difficult to explain under neutral evolution). Overall the results generally provide support for the neutral evolution of molecular markers.     

ALLOZYME VARIATION AMONG POPULATIONS OF BULINUS FORSKALII (EHRENBERG, 1831) (GASTROPODA: PLANORBIDAE) IN CAMEROON

Allozyme electrophoresis was used to study genetic diversityamong populations of the freshwater, hermaphroditic snail Bulinusforskalii in Cameroon. Three of 15 loci studied in 13 enzymesystems were polymorphic. Intrapopulation variation occurredin 8 of 32 populations sampled and heterozygotes were presentin 2 of these. Neither of these populations were in Hardy-Weinbergequilibrium. These findings are in agreement with reports thathave demonstrated a low genetic diversity in this very widelydistributed, eurytopic species and that have indicated thisspecies reproduces principally by self-fertilization. The restricteddistributions of rarer alleles in three loci may be due to anarrower habitat range for those phenotypes. For isocitratedehydrogenase and phosphoglucoisomerase, the faster alleleswere found throughout the range of B. forskalii extending fromthe Sahelian regions of the north to rain forest of the south.The slower, rarer alleles for these loci were restricted tothe equatorial rain forest regions. For hydroxybutyrate dehydrogenase,the opposite was true for the rarer allele, which was restrictedto a small region in the arid, tropical climate. (Received 27 April 1989; accepted 5 September 1989)     

Molecular evidence for a founder effect in invasive house finch (Carpodacus mexicanus) populations experiencing an emergent disease epidemic

The impact of founder events on levels of genetic variation in natural populations remains a topic of significant interest. Well-documented introductions provide a valuable opportunity to examine how founder events influence genetic diversity in invasive species. House finches (Carpodacus mexicanus) are passerine birds native to western North America, with the large eastern North American population derived from a small number of captive individuals released in the 1940s. Previous comparisons using amplified fragment length polymorphism (AFLP) markers found equivalent levels of diversity in eastern and western populations, suggesting that any genetic effects of the founder event were ameliorated by the rapid growth of the newly established population. We used an alternative marker system, 10 highly polymorphic microsatellites, to compare levels of genetic diversity between four native and five introduced house finch populations. In contrast to the AFLP comparisons, we found significantly lower allelic richness and heterozygosity in introduced populations across all loci. Three out of five introduced populations showed significant reductions in the ratio of the number of alleles to the allele size range, a within-population characteristic of recent bottlenecks. Finally, native and introduced populations showed significant pairwise differences in allele frequencies in every case, with stronger isolation by distance within the introduced than native range. Overall, our results provide compelling molecular evidence for a founder effect during the introduction of eastern house finches that reduced diversity levels at polymorphic microsatellite loci and may have contributed to the emergence of the Mycoplasma epidemic which recently swept the eastern range of this species.     

Biochemical assessment of evolution and taxonomy of the morphologically poorly diverged geckos, Gekko yakuensis and G. hokouensis (Reptilia: Squamata) in Japan, with special reference to their occasional hybridization

We assessed the validity of two gekkonid species, Gekko yakuensis and G. hokouensis, in southern Japan. We first assigned all 398 specimens into 18 samples merely on the basis of localities. By conducting significance test for deviations of genotype frequencies from Hardy‐Weinberg at 11 allozyme loci, we checked the reproductive unity of constituents in each of those local samples, and where necessary, rearranged them into subsamples on the basis of genetic markers so that we recognized minimum reproductively cohesive units. We then compared allele frequencies among all samples and subsamples examined. Results clearly indicated that all but two can be classified into two groups that can be discriminated from each other by remarkable allele frequency differences at four diagnostic loci, and by large genetic distances even between sympatric subsamples. Observations of morphological features of the samples and subsamples confirmed that the two groups correspond to G. yakuensis and G. hokouensis, supporting validities of these two species. Allele frequency comparisons, however, also revealed that the remaining two samples, both from southern Kyushu, possessed ‘marker alleles' of both G. yakuensis and G. hokouensis at all four diagnostic loci. These samples thus were considered to represent populations that have been derived through hybridization of the two species. Detailed analyses for genetic structures demonstrated that all hybrid genotypes in the two samples are post‐Fi generations with only one individual resulting from the back‐cross with a pure line population of G. yakuensis. This finding negates the possibility that the hybrid populations are maintained by a constant supply of newly produced Fj hybrids, but suggests that the hybrid genotypes constitute stable breeding populations. This implies that the genealogical independence of G. yakuensis and G. hokouensis in several other sympatric areas has been maintained by operations of some isolation mechanisms at a pre‐mating phase. Investigations of the morphological variation in each sample or subsample revealed that although the two species can be externally largely discriminated from each other by slight modifications of the currently used diagnoses, it is difficult to detect their hybrids based solely on the morphological features.     

First Microsatellite Loci of Red Mullet (<Emphasis Type="Italic">Mullus barbatus</Emphasis>) and Their Application to Genetic Structure Analysis of Adriatic Shared Stock

In order to study the genetic structure of the Adriatic shared stock of red mullet (Mullus barbatus), we developed a set of dinucleotide microsatellite markers. A dinucleotide-enriched genomic library was obtained, and 6 polymorphic dinucleotide loci were successfully optimized. The markers showed high expected heterozygosity (from 0.68 to 0.92) and allele number (from 12 to 33); thus they appear to be suitable for detecting genetic differences in the population of red mullet. Four Adriatic samples were subsequently analyzed for microsatellite variation, and the results showed subtle but statistically significant genetic differentiation, indicating that the Adriatic red mullet may group into local, genetically isolated populations. No correlation between geographic distance and genetic differentiation was observed. In addition, the evidence of recent bottlenecks in the Adriatic samples indicates that the observed population subdivision might reflect random local allelic variations, generated by reproductive success, survival rates, or fishing pressure.     

Population subdivision and gene flow among wild orangutans

Genetic variability among populations of orangutans from Borneo and Sumatra was assessed using seven SSR loci. Most SSR loci were highly polymorphic and their allele frequencies exhibited substantial variation across subpopulations. While significant genetic subdivision was observed among the island populations, genetic distance did not increase with geographic distance and sufficient gene flow persists to prevent marked genetic subdivision. Since it is unlikely that the Bornean Orangutans dispersed naturally among locations separated by such formidable geographic barriers, human assistance might already have altered their genetic structure. Our data suggests that there may be at least two subspecific clades of orangutans within Borneo while Central Kalimantan animals may have become more genetically related to animals in Sumatra due to human intervention.     

Genetic diversity of the house mouse Mus musculus and geographic distribution of its subspecies-specific RAPD markers on the territory of Russia

Genetic diversity and geographic distribution of taxon-specific RAPD markers was examined in ten local populations of the house mouse Mus musculus (n = 42). The house mice were generally characterized by moderate genetic variation: polymorphism P99 = 60%, P95 = 32.57%; heterozygosity H = 0.12; the observed allele number n(a) = 1.6; the effective allele number n(e) = 1.18; the within-population differentiation Theta = 0.388; and Shannon index I = 0.19. The degree of genetic isolation of individual local populations was greatly variable. The genetic subdivision index G(st) varied from 0.162 to 0.770 at the gene flow of Nm = 2.58-0.149, while the among-population distances D(N) varied from 0.026 to 0.178. of the largest part of the genetic diversity was found among the populations (H(T) = 0.125), while the within-population diversity was twice lower (H(S) = 0.06). The samples examined were well discriminated relative to the sets of RAPD markers. The character distribution pattern provided conditional subdivision of the mice into the "western" and the "eastern" groups with the putative boarder along the Baikal Lake. The first group was characterized by the prevalence of the markers typical of M. m. musculus and M. m. domesticus. The second group was characterized by the prevalence of the markers typical of M. m. musculus, M. m. gansuensis, M. m. castaneus, M. m. domesticus, and m. m. wagneri. The genotype of the nominative subspecies M. m. musculus was background for all populations. In the populations examined some of earlier described subspecies-specific molecular markers were found at different frequencies, pointing to the involvement of several subspecies of M. musculus in the process of hybridization.