Polymorphic Allozyme Research Articles

Genetic diversity within and divergence between rare and geographically widespread taxa of the Acacia acuminata Benth. (Mimosaceae) complex.

The Acacia acuminata complex is a group of woody shrubs and small trees comprised of three formally described taxa (A. oldfieldii, A. acuminata ssp. acuminata and ssp. burkittii) and two informal taxa ("small seed" and "narrow phyllode") with contrasting geographical distributions within the south-west of Western Australia. In addition, a series of variant populations of possible hybrid origin exist. Population genetic structure was investigated in 25 populations representing the taxa and variants using 16 polymorphic allozyme loci. All taxa and variants exhibited relatively high levels of genetic variation compared with other woody angiosperms with similar geographic distributions. Levels of genetic diversity in the widely distributed ssp. burkittii and "narrow phyllode" taxon were considerably higher (H(e), 0.311 and 0.319, respectively) than expected for widespread woody shrubs. In contrast, the rare and highly restricted A. oldfieldii exhibited significantly lower levels of genetic diversity (H(e), 0.173) compared with the other taxa in the complex, but higher than other rare woody shrubs. Although morphologically close, associations based on genetic distance showed A. oldfieldii was highly divergent from the other taxa (D = 0.85) while including variant populations confused systematic alliances. The unusual placement of some of these populations and high degree of population differentiation (G(ST), 12.7%) supports the suggestion that these may represent a series of hybridisation events between the various taxa.

Inversion and allozyme polymorphism show contrasting patterns of microgeographical population structure in a natural population of Drosophila buzzatii from Argentina

Abstract Second chromosome inversions and genotypic frequencies at seven allozyme loci were determined in a natural population of the cactophilic species Drosophila buzzatii that uses as breeding sites the necrotic cladodes of the prickly pear Opuntia quimilo and the rotting stems of cardón, Trichocereus terschekii. Different processes govern the evolutionary fate of inversion and allozyme polymorphisms. A pattern of heterotic balance for inversions seems to be acting uniformly in each breeding site and could depend on different regimes of density-dependent selection within cactus hosts. Patterns of variation of allozymes revealed significant heterogeneity in allele frequencies for Esterase-1 (Est-1) among O. quimilo rots and Aldehyde oxidase (Aldox) and Xanthine dehydrogenase (Xdh) among T. terschekii substrates and showed gene-cactus effects only for Esterase-2 (Est-2). Consistent and significant excesses of homozygotes were detected at both the within-rot and in the total population levels that could be accounted for by diversifying selection among individual breeding sites.

New molecular evidence that Teladorsagia circumcincta (Nematoda: Trichostrongylidea) is a species complex.

In the polymorphic Teladorsagia circumcincta (morphs circumcincta and trifurcata), a sheep and goat line (SGL) and a goat line (GL) have been previously described on the basis of the malate dehydrogenase allozyme polymorphism (MDH-2) and of the morphology of the dorsal ray. The GL were never found alone in 1 host, so the status of species was not given to these 2 lines. To investigate further whether there are other genetic markers that will delineate them, we collected T. circumcincta worms from goat and sheep at 8 farms in Touraine (west-central France). The worms were identified individually as being SGL or GL on the basis of MDH-2 polymorphism. This distinctiveness was corroborated by sequences of the beta-tubulin isotype I gene, the second internal transcribed spacer (ITS2) of their rDNA, and the nicotinamide dehydrogenase (ND4) gene of their mDNA. The extent of the divergence in the 3 additional genetic markers was such that SGL and GL may be considered as 2 species. A third putative species was found in the SGL line based exclusively on the ND4 gene. These findings suggest that T. circumcincta is a species complex and that further investigation is required on a wider geographic scale.

Genetic variation in populations of the morphologically and ecologically variable fern Stegnogramma pozoi subsp. mollissima (Thelypteridaceae) in Japan.

In Japanese Stegnogramma pozoi subsp. mollissima (Fisher ex Kunze) K. Iwats. there is the intrasubspecific variation among rbcL sequences. Northern and southern plants are genetically differentiated for maternally inherited cpDNA. In the present study we examined allozyme polymorphisms to test the hypothesis that northern and southern plants may be separate species. Based on allozyme data, the degree of gene flow among populations was estimated to be large. The artificial crossing experiments between cpDNA haplotypes also suggested that isolation has not developed among these cpDNA haplotypes. However, interpopulation genetic differentiation in cpDNA was observed even in the small area at the foot of Mt. Hakone, and the cpDNA haplotypes appear to have different habitat preferences.

Two Genetically Distinct Populations of Bobtail Squid, Euprymna scolopes, Exist on the Island of O'ahu

Population structure of the endemic Hawaiian bobtail squid, Euprymna scolopes, was examined using both morphological and genetic data. Although allozyme polymorphism was negligible, measurements of eggs, juveniles, and adults, as well as genetic data sequences of mitochondrial cytochrome oxidase I, demonstrated highly significant population structuring between two populations found on the northeastern and southern coasts of the island of O'ahu. These data suggest that extremely low levels of gene flow occur among these populations. Population subdivision of marine shallow-water invertebrates in Hawai'i is not expected based on earlier surveys, but may reflect a more general pattern for organisms, both marine and terrestrial, that exhibit limited dispersal. The subdivision also provides insight into the pathway through which coevolution between E. scolopes and its internal symbiont, Vibrio fischeri, may proceed.

Allozymic polymorphism and genetic differentiation among populations of Calomys musculinus and Calomys laucha (Rodentia: Muridae) from eastern Argentina

Summary The genetic variability and divergence among natural populations of Calomys musculinus and C. laucha from eastern Argentina were examined by protein electrophoresis of 24 loci. High levels of genetic variability were found in both species when compared to other rodents and mammals. Mean expected heterozygosity (He) ranged from 0.112 to 0.156, proportion of polymorphic loci (P 95% ) from 37.5% to 50% and mean number of alleles per locus (A) of 1.6-1.7 for C. musculinus . H e from 0.097 to 0.126, P 95% from 34.8 to 39.1 and A from 1.7 to 1.9 were the values for C. laucha . Populations of this last species revealed a higher degree of geographical differentiation (Θ = 0.017, P C. musculinus (Θ = 0.002, P > 0.05). These results are in agreement with the known social structure and habitat of both species. C. musculinus is an opportunistic species, with a loose social structure and a predominance of transient over resident animals, indicating a high ambulatory activity. C. laucha , on the contrary, inhabits almost exclusively cultivated fields, and evidence of social stratification has been reported for this species.

Allozyme polymorphisms of maize populations from southwestern China.

Maize ( Zea mays L.) is one of the most-important food crops in southwestern China. The diversity of maize populations from southwestern China has been evaluated on the basis of agronomic and morphological data, but not on marker data. Our objectives were to evaluate the allozyme polymorphism of these populations, and group the populations on the basis of allozyme data. We analyzed 27 maize populations from southwestern China and two populations [BS13(S)C2 and Lancaster] from the USA for genetic variation at 18 allozyme loci. We found a total of 69 alleles at 18 allozyme loci with an average of 3.8 alleles per locus. Compared with inbreds, hybrids, and populations from the U.S. Corn Belt, the 27 Chinese populations had a significantly higher ( p<0.01) number of allozyme alleles per locus. Maize populations from southwestern China have accumulated abundant genetic diversity, and might be valuable germplasm for broadening the genetic base of U.S. Corn Belt breeding germplasm. The analyses of allele-frequency distributions and the expected heterozygosity also reflected the differences between the Chinese and the U.S. germplasm. The Chinese populations might be valuable germplasm for complementing U.S. Corn Belt breeding germplasm. The analysis of gene diversity showed that 77% of the allozyme variation resided within populations and 23% between populations. This result suggested that breeders should identify one or a few Chinese populations with the best agronomic performance, and exploit the genetic variation within these selected populations. Cluster analysis classified the 29 populations into four main groups. Groupings based on allozyme data could be useful for classifying the populations into different heterotic groups and, consequently, exploiting them in hybrid breeding.

Genetic monitoring of brackish-water populations: the Mediterranean toothcarp Aphanius fasciatus (Cyprinodontidae) as a model

The measurement of genetic variability and assessment of population genetic losses are important components of environmental management programs. Twenty-three natural populations of the Mediterranean brackish-water toothcarp Aphanius fasciatus were investigated using different statistical approaches based on genetic data at 13 polymorphic allozyme loci. In general, no differ- ences between values of within-population genetic variability estimates occurred. The Wilcoxon sign-rank test for heterozygosity excess due to a recent bottleneck was conducted on the array of populations. In addition, a qualitative descriptor of allele frequency distribution was used to infer bottlenecks. Only populations from the Orbetello lagoon and La Salina at Elba Island revealed sig- nificant heterozygosity excess under both the infinite allele model (IAM) and stepwise mutation model (SMM). A recent dystrophic crisis may account for the genetic loss detected in the population of A. fasciatus from the Orbetello lagoon, whereas exceptionally high predation pressure and/or the increased mortality rate created by local hydrological conditions could be responsible for the bottle- neck in the population at La Salina. Tests for bottlenecks have proved effective tools for genetic monitoring of A. fasciatus populations.

Extensive genetic divergence among populations of the Australian freshwater fish, Pseudomugil signifer (Pseudomugilidae), at different hierarchical scales

The 'island' nature of river systems limits the possibility of dispersal in freshwater fish species, with many displaying extensive genetic subdivision across their ranges. We examined the population genetic structure of the predominantly freshwater fish, Pseudomugil signifer, at fine, medium and broad scales using allozyme and mitochondrial DNA techniques. Extensive genetic subdivision across the range (FST = 0.6) at six polymorphic allozyme loci was partitioned mostly among river-system drainages (42%). Patterns of mitochondrial DNA sequences, which mirrored previous taxonomic designations and a terrestrial biogeographic barrier, identified two major groups. The level of divergence between the groups implied a considerable period of isolation. At a more localized scale, significant genetic differences between adjacent drainages implied that flood events are not effective transport mechanisms and indicate that populations of P. signifer in different drainages are essentially independent units. The history of P.�signifer appears to be dominated, at different spatial scales, by long periods of isolation among drainages mediated by changes in sea-level, which merge and isolate drainages haphazardly over time. The chance nature of dispersal, coupled with isolation and potential population size fluctuations, probably leads to the observed complex patterns of genetic divergence.

Managing fish populations under mosaic relationships. The case of brown trout (Salmo trutta) in peripheral Mediterranean populations

Brown trout were collected from 36 locations inthe Iberian Peninsula representing thesouthwestern extreme of this species'distribution in Mediterranean drainages.Allelic distributions among these peripheralpopulations for 26 polymorphic allozyme loci(corrected to remove effects of introgressionfrom exogenous hatchery introductions)indicated a mosaic pattern both within andamong drainages. This distribution wasinterpreted to reflect reticular evolutionaryprocesses involving multiple colonizationepisodes by distinct lineages, secondaryintergradations, and drift. Under thisscenario, management to conserve native genepools differs from that commonly used underhierarchical structures (such as in AtlanticIberian drainages) where geographic patternscould justify regional stocking of indigenousfish in adjacent unsampled areas. Because suchaction risks erosion of native populations inthe present case, remedial efforts should focuson habitat recovery and environmental educationprograms, and harvest sustained by naturalreproduction.

Estrutura genética de populações naturais de Cryptocarya aschersoniana Mez (Lauraceae) através de marcadores isoenzimáticos

Pela análise de 39 locos isoenzimáticos polimórficos, estimaram-se as freqüências alélicas referentes a 267 indivíduos de 12 populações naturais de Cryptocarya aschersoniana provenientes de Florestas de Planalto do estado de São Paulo e sul de Minas Gerais, Brasil. Foram obtidas estimativas das estatísticas F de Wright pelo método da análise da variância para estimação não viesada dos parâmetros correspondentes F=F IT, θ P =F ST e f=F IS. Os valores médios obtidos de F^ resultaram em 0,552 &lt; 0,415 &lt; 0,275; os de θ^P foram 0,395 &lt; 0,335 &lt; 0,279; e os de f^ sendo 0,292 &lt; 0,119 &lt; -0,039. Esses resultados indicaram que os indivíduos dentro das populações devem ser panmíticos e que a diversidade entre populações foi bastante alta, sendo superior à que poderia se esperar para famílias com estruturação de irmãos-germanos. Calculando-se θ^P com as populações tomadas duas a duas, testou-se o modelo de isolamento pela distância que se mostrou inadequado para explicar a divergência encontrada entre as populações. O fluxo gênico estimado de 0,4 indivíduos por geração corroborou a pronunciada diferenciação populacional. Devido aos valores insignificantes encontrados de fˆ @ F^IS, o tamanho efetivo de variância de cada população foi equivalente ao número de indivíduos amostrados. Sob um contexto metapopulacional, considerando-se as 12 populações amostradas para a espécie, o tamanho efetivo populacional foi de 15,4 indivíduos (5,77%) para o total amostrado, indicando que a amostragem de diferentes populações deve ser uma estratégia importante para seu manejo.

Stratified analysis of the soil seed bank in the cedar glade endemic Astragalus bibullatus: evidence for historical changes in genetic structure

Persistent seed banks may provide information on historical changes in the genetic composition of populations. We used stratified sampling of the soil seed bank of Astragalus bibullatus (Pyne's ground plum) to assess levels of temporal variation in population genetic structure and to infer historical changes in the levels of inbreeding and relative gene flow. This species has an extremely limited distribution in the Central Basin of Tennessee, where it is found in open areas and along the edges of cedar glades. Protein electrophoresis was conducted on seedlings grown from seeds that had been recovered from three successive 1 cm thick layers of soil sampled from six sites. Analyses of seven polymorphic allozyme loci indicated that there were substantial levels of genetic differentiation among soil layers and sites. Higher levels of genetic diversity were found in seed than in vegetative populations that had been sampled in a previous study. Seed populations from the uppermost soil layer had higher heterozygote deficiencies, displayed higher levels of differentiation among sites, and had higher private allele frequencies than seed populations from the lower two layers. The change in heterozygosity and distribution of genetic variation among sites for the youngest soil layer is consistent with a pattern of increased selfing, sib mating, and decreased gene flow among populations. These changes in inbreeding and relative levels of gene flow are corroborated by information on historical land use practices in the region and support the hypothesis that loss of appropriate habitat has led to smaller population sizes and a more fragmented distribution of this cedar glade endemic.

Microsatellite DNA analysis of population structure in Atlantic herring (Clupea harengus), with direct comparison to allozyme and mtDNA RFLP analyses

Previous attempts to test for small-scale stock structuring within Atlantic herring (Clupea harengus L.) with molecular markers have been hampered by uninformative levels of genetic variation. Here we report the first application of microsatellite DNA markers to investigate population subdivision in Atlantic herring from Norwegian waters and the Barents Sea, and also examine microsatellite differentiation between C. harengus and Pacific herring (C. pallasi). Results from four microsatellite loci indicate high, and informative, variation compared to molecular markers used previously: number of alleles per locus=18–41; mean expected heterozygosity within samples=0.90–0.93. Significant genetic differences were detected between almost all samples representing postulated Icelandic summer-spawner, Norwegian spring-spawner and Norwegian fjord stocks, using Fisher’s exact test, FST and RST values. Levels of allele frequency differentiation between Atlantic and Pacific herring overlapped the range seen among Atlantic herring samples, indicating that microsatellites are poor indicators of the degree of species differentiation. Comparison with allozyme and mitochondrial DNA restriction fragment length polymorphism (RFLP) datasets from the same samples suggests that microsatellites may detect structuring at a finer scale, but are less informative at larger scales of divergence.

VNTR variability in Atlantic poor cod ( Trisopterus minutus minutus) throughout its range: single locus minisatellite data suggest reproductive isolation for the Faroe Bank population

Nine samples of Atlantic poor cod, Trisopterus minutus minutus, collected from the Bay of Biscay to Trondheimsfjord, Norway, were analysed using three minisatellite DNA loci, amplified using PCR and screened with an automated sequencer. One locus was found to be polymorphic. F ST analysis using the polymorphic locus indicated that 2.2% of the total genetic diversity detected was due to differences among samples ( F ST=0.022; P<0.001). The only significant pair-wise heterogeneity was found between the Faroe Bank and each of the other samples. This is consistent with previous analyses of the same samples using 11 polymorphic allozyme loci.

MORPHOLOGICAL AND MOLECULAR ANALYSIS OF THE STATUS AND RELATIONSHIPS OF THE LAND SNAIL `CERNUELLA' USTICENSIS (CALCARA, 1842) (STYLOMMATOPHORA: HELICOIDEA)

The revision of ‘Cernuella’ usticensis, an helicelline hygromiid, was based on the analysis of morphological characters and on the genetic study of allozyme patterns. The morphological study demonstrates that C. usticensis can be distinguished from all the other Cernuella species by the presence of a dart sac complex with basal vaginal outgrowth, inner sac with thin walls and large lumen, and a less-developed ‘dart-gun’. Analysis of allozyme polymorphisms, performed to test its relationships to other Cernuella species, namely C. virgata, C. cisalpina, C. caruanae, C. amanda and C. neglecta confirms that ‘C.’ usticensis is distinct from all those examined. Parsimony analysis of the morphological characters of all taxa included in the helicelline hygromiids (hygromiids with pedal innervation of penis) suggests that it forms a monophyletic group with Ichnusomunda based on the inner sac structure (with thin walls and large lumen). Unfortunately, material of the only species of Ichnusomunda, I. sacchii, was not available for allozyme analysis, and consequently it has not been possible to test this hypothesis genetically. Since homoplasies cannot be ruled out (inner sac with thin walls and wide lumen are known in other hygromiids), its inclusion in Ichnusomunda must await further evidence.

Heterosis in two closely related species of earthworm (Eisenia fetida and E. andrei).

The importance of heterosis, and in particular allozyme-associated heterosis, in natural populations remains unclear. Much of the scepticism that surrounds allozyme-associated heterosis comes from inconsistent and unreliable detection of the relationship. Thus, evaluating the genetic mechanisms that may cause allozyme-associated heterosis in natural populations has proven difficult. The most prevalent hypotheses that have been put forward to explain the genetic basis of heterosis are the general dominance and the local overdominance hypotheses. A factorial crossing design was used to survey eight polymorphic allozyme loci in the parent and offspring generations of two species of earthworms in order to evaluate possible mechanisms of allozyme-associated heterosis for growth rate. Significant heritable variation for growth rate was detected only within a single cross. Allozyme-associated heterosis for growth rate was detected only within this cross. This relationship did not persist after the effects of interfamily variation were removed. These results indicate that simple heritability of a fitness-related trait may be necessary for predictive power and repeatability of allozyme-associated heterosis, and that the allozyme-associated heterosis detected in this study was the result of general dominant genetic effects.

Allozyme polymorphisms in tetraploid potato gene pools and the effect on human selection

The need for broadening a crop’s genetic base may be determined by comparing allele frequencies within the gene pools of farmer selections in their centers of diversity with that of modern breeding populations. The genetic structure of Andean and Chilean potato farmer selections was investigated with the aid of nine isozymes, which have been studied in detail and used to characterize North American cultivars and advanced breeding lines. These isozymes are associated with the most-important agronomic or quality characters in the North American gene pool. By comparing these data with previous analyses of the North American gene pool, allozyme frequency changes for nine loci were monitored. Allozyme frequency changes were not always due to genetic drift, but resulted also from directional selection of isozyme marker linked quantitative trait loci (QTLs) affecting agronomic or quality characters. Changes in allozyme frequency can also occur as a consequence of pleiotropy, i.e. the isozyme itself may be involved in the expression of a phenotype. These allozyme frequency changes may reflect the manipulation of the potato genome by breeders. There were allozymes in some North American cultivars that were not observed in the farmer selections from the Andes and Chile. This confirms that breeders have already introgressed exotic genes from wild and other primitive cultivated tuber-bearing Solanum species. On this basis, the need for broadening the genetic base for specific chromosomes (or chromosome regions) should be based on analysis with these and other genetic markers available in potato.

Humid forest refugia, speciation and secondary introgression between evolutionary lineages: differentiation in a Near Eastern brown frog, Rana macrocnemis

Brown frogs of the complex Rana macrocnemis demonstrate various degrees of differentiation between the two widespread forms, macrocnemis and camerani, in different parts of Anatolia, the Caucasus Isthmus and northern Iran. In order to reveal whether or not the forms represent monophyletic evolutionary lineages, we analysed the geographic distribution of characters of external morphology, alleles at three polymorphic allozyme loci and mitochondrial DNA haplotypes. All three character sets showed a highly congruent pattern in a limited area of humid forests in the south-west Caucasus. Frogs from this area (form macrocnemis) represent a monophyletic lineage which forms a narrow hybrid zone with populations of camerani inhabiting the southern Caucasus and north-east Turkey. However, in other parts of the group's range, hybridization between the two lineages resulted in the merger of forms and the formation of a clinal pattern of variations. The role of landscape-dependent diversifying selection in the evolution of the group is discussed. Conceptual difficulties in delimiting the borders of subspecies are pointed out.

Humid forest refugia, speciation and secondary introgression between evolutionary lineages: differentiation in a Near Eastern brown frog, Rana macrocnemis

Brown frogs of the complex Rana macrocnemis demonstrate various degrees of differentiation between the two widespread forms, macrocnemis and camerani, in different parts of Anatolia, the Caucasus Isthmus and northern Iran. In order to reveal whether or not the forms represent monophyletic evolutionary lineages, we analysed the geographic distribution of characters of external morphology, alleles at three polymorphic allozyme loci and mitochondrial DNA haplotypes. All three character sets showed a highly congruent pattern in a limited area of humid forests in the south-west Caucasus. Frogs from this area (form macrocnemis) represent a monophyletic lineage which forms a narrow hybrid zone with populations of camerani inhabiting the southern Caucasus and north-east Turkey. However, in other parts of the group's range, hybridization between the two lineages resulted in the merger of forms and the formation of a clinal pattern of variations. The role of landscape-dependent diversifying selection in the evolution of the group is discussed. Conceptual difficulties in delimiting the borders of subspecies are pointed out.

Regional Differentiation in Genetic Components for the American Beech, Fagus grandifolia Ehrh., in Relation to Geological History and Mode of Reproduction

, were investigated throughout its geographical range, using allozyme polymorphisms. A total of 1,131 trees from 21 populations were examined for 32 alleles of 10 polymorphic and two monomorphic loci in eight enzyme systems. The mean expected heterozygosity was 0.186, which indicates a relatively high genetic diversity within the populations. The levels of population differentiation were high, as revealed by genetic parameters, i.e., G ST =0.168 and F ST =0.167. The results of principal component analysis on allele frequencies clearly revealed unique regional patterns of differentiation in genetic components among populations “with” and “without” vegetative regeneration by root suckers. The American beech populations consist of two genetically distinct clusters, one from the Gulf-coastal plain, eastern coastal plain, Piedmont Plateau and Ozark Plateau; and the other from the remaining northern glaciated territories. Populations from the Blue Ridge and Great Smoky Mountains turned out to belong to the latter cluster, which is also characterized by extensive regeneration via root suckers. The consequences of regional differentiation in genetic components are discussed in relation to the postglacial spread from refugia to the current geographic distributions and the mode of reproduction.