Estimating total genic diversity in the house mouse

In a survey of variation in both electrophoretic charge and thermostability at 14 structural loci in 40 strains of Mus musculus, 27 electromorphs (polypeptides differing in electrophoretic charge) and 20 thermomorphs (polypeptides differing in thermostability) were found. Electrophoresis detected 11 new variants within thermomorphs, and the heat denaturation technique detected four new variants within electromorphs. From these data, and making the assumption that both techniques are independent of each other, it is estimated that the actual total number of alleles at the 14 loci is 53, or an average of 3.79 per locus (1.96 per electromorph), and that electrophoresis apparently detects one-third of the variants, thus describing about 50% of the alleles at structural gene loci in the house mouse.     

Reconstruction of caribou evolutionary history in Western North America and its implications for conservation

The role of Beringia as a refugium and route for trans-continental exchange of fauna during glacial cycles of the past 2million years are well documented; less apparent is its contribution as a significant reservoir of genetic diversity. Using mitochondrial DNA sequences and 14 microsatellite loci, we investigate the phylogeographic history of caribou (Rangifer tarandus) in western North America. Patterns of genetic diversity reveal two distinct groups of caribou. Caribou classified as a Northern group, of Beringian origin, exhibited greater number and variability in mtDNA haplotypes compared to a Southern group originating from refugia south of glacial ice. Results indicate that subspecies R. t. granti of Alaska and R. t. groenlandicus of northern Canada do not constitute distinguishable units at mtDNA or microsatellites, belying their current status as separate subspecies. Additionally, the Northern Mountain ecotype of woodland caribou (presently R. t. caribou) has closer kinship to caribou classified as granti or groenlandicus. Comparisons of mtDNA and microsatellite data suggest that behavioural and ecological specialization is a more recently derived life history characteristic. Notably, microsatellite differentiation among Southern herds is significantly greater, most likely as a result of human-induced landscape fragmentation and genetic drift due to smaller population sizes. These results not only provide important insight into the evolutionary history of northern species such as caribou, but also are important indicators for managers evaluating conservation measures for this threatened species.     

Associations of allozyme variation and behavior in the cowpea weevil (Callosobruchus maculatus)

The cowpea weevil (Callosobruchus maculatus (Fabré)) exhibits several behavioral traits that are stable within, but vary among, strains. These traits are heritable and quantitative. We used cellulose acetate gel electrophoresis to quantify allozyme variation within and among laboratory cultures of four weevil strains and determine whether allozyme variation correlates with behavioral traits. Significant variation exists at 8 of 11 loci assayed and gene frequencies are significantly different among strains. The South Indian strain (SI) is most variable and measures of genetic distance set it apart from the other strains. It is also behaviorally unique. The Brazilian strain (BC) is most different from SI in allozyme diversity and behavioral phenotype, while two African strains (IITA, CAM) are intermediate in allozyme diversity and phenotype. These results are consistent with the known history of these strains and the differences in the allozymes parallel the differences in behavioral traits.     

Response of tundra ecosystem in southwestern Alaska to Younger-Dryas climatic oscillation

Climatic warming during the last glacial–interglacial transition (LGIT) was punctuated by reversals to glacial‐like conditions. Palaeorecords of ecosystem change can help document the geographical extent of these events and improve our understanding of biotic sensitivity to climatic forcing. To reconstruct ecosystem and climatic variations during the LGIT, we analyzed lake sediments from southwestern Alaska for fossil pollen assemblages, biogenic‐silica content (BSiO₂%), and organic‐carbon content (OC%). Betula shrub tundra replaced herb tundra as the dominant vegetation of the region around 13 600 cal BP (cal BP: ¹⁴C calibrated calendar years before present), as inferred from an increase of Betula pollen percentages from << 5% to >> 20% with associated decreases in Cyperaceae, Poaceae, and Artemisia. At c. 13 000 cal BP, a decrease of Betula pollen from 28 to << 5% suggests that shrub tundra reverted to herb tundra. Shrub tundra replaced herb tundra to resume as the dominant vegetation at 11 600 cal BP. Higher OC% and BSiO₂% values suggest more stable soils and higher aquatic productivity during shrub‐tundra periods than during herb‐tundra periods, although pollen changes lagged behind changes in the biogeochemical indicators before c. 13 000 cal BP. Comparison of our palaeoecological data with the ice‐core dδ¹⁸O record from Greenland reveals strikingly similar patterns from the onset through the termination of the Younger Dryas (YD). This similarity supports the hypothesis that, as in the North Atlantic region, pronounced YD climatic oscillations occurred in the North Pacific region. The rapidity and magnitude of ecological changes at the termination of the YD are consistent with greenhouse experiments and historic photographs demonstrating tundra sensitivity to climatic forcing.     

Refugia, differentiation and postglacial migration in arctic-alpine Eurasia, exemplified by the mountain avens (Dryas octopetala L.)

Many arctic-alpine organisms have vast present-day ranges across Eurasia, but their history of refugial isolation, differentiation and postglacial expansion is poorly understood. The mountain avens, Dryas octopetala sensu lato, is a long-lived, wind-dispersed, diploid shrub forming one of the most important components of Eurasian tundras and heaths in terms of biomass. We address differentiation and migration history of the species with emphasis on the western and northern Eurasian parts of its distribution area, also including some East Greenlandic and North American populations (partly referred to as the closely related D. integrifolia M. Vahl). We analysed 459 plants from 52 populations for 155 amplified fragment length polymorphisms (AFLP) markers. The Eurasian plants were separated into two main groups, probably reflecting isolation and expansion from two major glacial refugia, situated south and east of the North European ice sheets, respectively. Virtually all of northwestern Europe as well as East Greenland have been colonized by the Southern lineage, whereas northwest Russia, the Tatra Mountains and the arctic archipelago of Svalbard have been colonized by the Eastern lineage. The data indicate a contact zone between the two lineages in northern Scandinavia and possibly in the Tatra Mountains. The two single populations analysed from the Caucasus and Altai Mountains were most closely related to the Eastern lineage but were strongly divergent from the remaining eastern populations, suggesting survival in separate refugia at least during the last glaciation. The North American populations grouped with those from East Greenland, irrespective of their taxonomic affiliation, but this may be caused by independent hybridization with D. integrifolia and therefore not reflect the true relationship between populations from these areas.     

Postglacial genetic differentiation of reproductive ecotypes of kokanee Oncorhynchus nerka in Okanagan Lake, British Columbia

Okanagan Lake, south-central interior of BC, contains two reproductive ecotypes of kokanee Oncorhynchus nerka ; individuals spawn in tributary streams ('stream-spawners') as well as on shoreline gravel areas ('beach-spawners'). We tested the hypothesis that these sympatric ecotypes comprise a single panmictic population by assaying variation in morphological traits and at allozyme, mitochondrial and minisatellite DNA loci in fish collected from three stream-spawning and two beach-spawning sites. No morphological traits consistently distinguished the reproductive ecotypes with the exception of the number of anal fin rays which was greater in stream-spawning kokanee. Four of 18 allozyme loci screened were polymorphic, but no significant allele frequency differences were detected among populations within ecotypes or between ecotypes. Similarly, allele frequencies at two minisatellite DNA loci were not significantly different among populations or between ecotypes. By contrast, significant differences in the frequencies of mitochondrial DNA restriction fragment length polymorphism (mtDNA RFLP) haplotypes were detected between stream- and beach-spawners, but not among populations within ecotypes. Further, two RFLPs that distinguished stream- and beach-spawning adults were found in juvenile kokanee sampled from the limnetic zone of Okanagan Lake. The two mtDNA RFLPs and a d-loop sequence variant appear to be unique to Okanagan Lake kokanee because we did not observe these haplotypes in sockeye salmon and kokanee sampled outside of Okanagan Lake. Our data suggest that: (i) there is restricted female-mediated gene flow between stream- and beach-spawning kokanee in Okanagan Lake, (ii) the forms have diverged within the lake basin since the retreat of the Wisconsinian glaciers (< ≊ 11 000 years ago), and (iii) distinct reproductive niches may promote divergence in north temperate freshwater fish faunas.     

Allozyme variations in six natural populations of scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis>) in Turkey

Genetic variation in six natural populations of Scots pine (Pinus sylvestris L.) was determined with isoenzyme analyses. For this purpose, haploid female gametophytes of seeds and horizontal starch gel electrophoresis technique were used. A total of 17 loci and 58 alleles were observed in studying 10 enzyme systems. The average proportion of polymorphic loci for populations ranged from 58.8% to 70.6%. The average number of alleles per locus per population was 2.65. The mean estimated expected heterozygosity (He) of populations was 0.294. A rather high proportion of genetic diversity (96.4%) was due to within-population variation and the remaining (3.6%) was due to variation among populations. The level of gene flow (N_em) was found to be 6.69 per generation. Nei’s genetic distance coefficient ranged from 0.006 to 0.027 (mean 0.017) among all possible population pairs. The mean value of Nei’s genetic distance is similar to the values reported for other European Scots pine populations. The low mean value of Nei’s genetic distance among populations is enough to explain low interpopulation variation. According to genetic variation parameters, three out of six populations (Akdagmadeni-Yozgat, Refahiye-Erzincan and Vezirkopru-Samsun) appear to be preferable populations for genetic conservation and forest tree breeding programs.     

Allozyme and microsatellite genetic variation in natural samples of zebrafish,Danio rerio

In this paper, we report the results from allozyme and microsatellite markers in natural populations of the zebrafish, a species of great significance in biological studies. Four zebrafish wild samples from West Bengal, India, were analysed in a preliminary survey of levels and patterns of genetic variation. Results indicate high levels of genetic variability and weak genetic structure, although the latter is consistent with the geographical features of the area under study, sampling sites being located in the Ganges and Brahmaputra delta region, which is characterized by high waterways connectivity.     

Protein polymorphism in natural populations of Diachasmimorpha longicaudata (Hymenoptera: Braconidae) in Thailand

Diachasmimorpha longicaudata (Ashmead) is a larval parasitoid of tephritid flies and is widely used as a classical biological control agent. We have used allozyme electrophoresis to evaluate the genetic relationships of six populations of D. longicaudata in Thailand. Twelve loci were examined of which 11 were polymorphic in at least some populations, especially that of Nakornratchasima. We observed a complete lack of heterozygotes for seven of the 10 polymorphic loci in the Nakornratchisima female population, and a significant deficiency of heterozygotes at a further two loci. We discuss possible hypotheses for these findings in light of the haplo-diploid sex determination system of these wasps. This revised version was published online in July 2006 with corrections to the Cover Date.     

Geographic differentiation between populations of Rhinocyllus conicus Frölich (Coleoptera: Curculionidae): concordance of allozyme and morphometric analysis

The weevil Rhinocyllu conicus develops only in the flowerheads of thistles {Asteracea; Carduineae) and therefore it is used as a biocontrol agent against thistle weed species. Populations out of 14 regions within its natural distribution area (from the Atlantic coast in the west to Israel in the east) were analysed by means of allozymes and morphometries. In both analyses the 14 populations were grouped into two concordant units. Based on nine scored loci (six of them polymorphic), mean Nei's genetic distance between the two groups was 0.073. In a reclassification test following DFA of morphometric data, 93.2% of all individuals were grouped back into the correct group. The two groups were considered to belong to a temperate and a Mediterranean subspecies respectively, the latter probably identical to the formerly described Rhinocyllus oblongus .     

Genetic variation and ecology of stoneroller minnows

Genetic variation at 17 enzymic and other protein loci was examined for natural populations of stoneroller minnows, Campostoma oligolepis and C. anomalum. Species differences in levels of heterozygosity, standardized variance of gene frequencies and interpopulation heterogeneity appear to be a function of degree of demic isolation, rate of migration and potential for stochastic processes to structure genomes.