THE GEOGRAPHY OF MITOCHONDRIAL DNA VARIATION,POPULATION STRUCTURE,HYBRIDIZATION, AND SPECIES LIMITS IN THE FOX SPARROW (PASSERELLA ILIACA)

Geographic variation in mitochondrial DNA (mtDNA) restriction sites was studied in the fox sparrow (Passerella iliaca). Seventy-eight haplotypes were found. Haplotypes fall into four phylogeographic groups that correspond to groups defined by plumage characters. The geographic distribution of these four groups does not appear congruent with mtDNA patterns in other vertebrates. Within each group, there is little geographic variation in mtDNA restriction sites, although there is geographic variation in plumage coloration and body size. The evolution of mtDNA diversity in fox sparrows seems best explained by vicariant events rather than isolation by distance. The mtDNA evidence suggests that Passerella megarhyncha and Passerella schistacea, two nonsister taxa that occur in western North America, have independently undergone bottlenecks. Hybridization is limited between all pairs of taxa except P. megarhyncha and P. schistacea, where mtDNA evidence suggests a narrow contact zone along the interface of the Great Basin and Sierra Nevada/Cascades. Morphometric characters intergrade over a broader area, suggesting that different processes are responsible for the two gradients. The occurrence of limited backcrossing among taxa suggests that cytoplasmic-nuclear incompatibility is lacking. The number of biological species would range from one to four, depending on the degree of hybridization tolerated. The mtDNA and plumage characters suggest four phylogenetic species: P. iliaca, P. megarhyncha, P. unalaschcensis, and P. schistacea.     

中华鲟年龄鉴别和繁殖群体结构的研究

本文研究中华鲟的年龄鉴别和葛洲坝枢纽工程大江截流后1981—1982年群集于坝下的宜昌至石首江段的中华鲟繁殖群体结构的特点。根据匙骨大小与中华鲟长度呈显著相关推算了中华鲟在海洋中的生长速度,计算了体长和体重的函数值及尾叉体长、体重和胸围的复相关。根据鳍条骨和匙骨年轮排列格局特点计算了中华鲟初次产卵和重复产卵的比例,同时,就宽区宽带轮和狭区狭带轮交替过程反映的生物学特征作了初步分析与探讨。     

MITOCHONDRIAL DNA VARIATION IN THE FIELD VOLE (MICROTUS AGRESTIS): REGIONAL POPULATION STRUCTURE AND COLONIZATION HISTORY

Restriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA) was used to examine the genetic structure among field voles (Microtus agrestis) from southern and central Sweden. A total of 57 haplotypes was identified in 158 voles from 60 localities. Overall mtDNA diversity was high, but both haplotype and nucleotide diversity exhibited pronounced geographic heterogeneity. Phylogenetic analyses revealed a shallow tree with seven primary mtDNA lineages separated by sequence divergences ranging from 0.6% to 1.0%. The geographic structure of mtDNA diversity and lineage distribution was complex but strongly structured and deviated significantly from an equilibrium situation. The extensive mtDNA diversity observed and the recent biogeographic history of the region suggests that the shallow mtDNA structure in the field vole cannot be explained solely by stochastic lineage sorting in situ or isolation by distance. Instead, the data suggest that the genetic imprints of historical demographic conditions and vicariant geographic events have been preserved and to a large extent determine the contemporary geographic distribution of mtDNA variation. A plausible historical scenario involves differentiation of mtDNA lineages in local populations in glacial refugia, a moving postglacial population structure, and bottlenecks and expansions of mtDNA lineages during the postglacial recolonization of Sweden. By combining the mtDNA data with an analysis of Y-chromosome variation, a specific population unit was identified in southwestern Sweden. This population, defined by a unique mtDNA lineage and fixation of a Y-chromosome variant, probably originated in a population bottleneck in southern Sweden about 12,000 to 13,000 calendar years ago.     

VARIATION IN MITOCHONDRIAL DNA OF AEDES SPECIES (DIPTERA: CULICIDAE)

Relationships among seven species of the Aedes scutellaris subgroup and four of the Aedes albopictus subgroup were determined using restriction fragment analysis of mtDNA. Considerable polymorphism was found among species, with an average proportion of 0.338 restriction fragments being shared among them. Fitch-Margoliash, Wagner parsimony and UPGMA analyses revealed that the phylogeny based on mtDNA was only partially congruent with that based on allozymes and morphology. All three analyses, however, suggested that three species pairs, A. flavopictus-A. pseudalbopictus, A. pseudoscutellaris-A. riversi, and A. albopictus-A. polynesiensis were monophyletic with regard to their mtDNA. The results indicated that although the species in the A. scutellaris and the A. albopictus subgroups do not exhibit significant morphological divergence, their mtDNA has diverged extensively.     

雀形目10种鸟类线粒体的DNA变异及分子进化

采用14种限制性内切酶（Apa I、BamHI、Bgl Ⅱ、EcoRI、EcoRV、HindⅢ、HpaI、KpnI、PstI、PuvⅡ、SalI、ScaI、XbaI和XhoI）对雀形目3科10种鸟类（蒙古百灵、喜鹊、小嘴乌雅、白腰朱顶雀、锡嘴雀、朱雀、红腹灰雀、灰腹灰雀、红交嘴雀和黄喉Wu）进行限制性片段长度多态分析（RFLP分析）。结果表明：雀形目鸟类基因组大小存在遗传多态性,不同类群在酶切类型上表现出各自的特点,雀形目鸟类与非雀形目鸟类在线粒体DNA的进化速率有着相同的特点,化石记录的地质年代与线粒体DNA分子时钟记录的年代有着惊人的吻合,这两个互为独立事件的统一,提示线粒体DNA作为分子进化的良好工具。     

小熊猫种群遗传结构和地理分化

本文采用分子系统地理学的研究方法 ,对我国小熊猫 (Ailurusfulgens)地理分布格局的形成原因进行了探讨。我们从四个地理单元的 32号样品中成功地扩增出了 371bp的线粒体DNA控制区片段 ,在所有可比较的 35 7bp的序列中 ,发现 2 9个变异位点 ,其中转换和颠换分别为 2 1和 8,没有插入 /缺失。在四个地理单元中 ,共有 16种线粒体DNA单倍型 ,且在各地理单元中都具有较高的单倍型的多态性。进一步分析表明 ,各单倍型之间的遗传距离平均为 1 6 0 % ,76 5 9%的遗传差异发生在地理单元间 ,仅 2 3 4 1%发生在单元内。分子变异分析和系统重建结果也表明 ,各地理单元之间不存在共享的单倍型 ,YN (云南地理单元 )与XL (相岭地理单元 )和QL (邛崃地理单元 )之间存在着显著的遗传分化 ,FST分别为 0 336和 0 35 1(P <0 0 0 1) ,其余地理种群之间分化不明显 (P >0 0 5 ) ,单倍型缺乏比较明显的地理分布格局 ,各地理单元中的单倍型相互散布在不同的分布群中。经Fs检验 (Fs=- 10 12 1) ,并结合化石资料 ,我们认为由于受第四纪气候和环境变化的影响 ,小熊猫种群在进化过程中曾经历种群暴发而不断扩散 ,从而形成今天的分布格局。     

THE EFFECT OF ETHIDIUM BROMIDE ON MITOCHONDRIAL DNA SYNTHESIS AND MITOCHONDRIAL DNA STRUCTURE IN HELA CELLS

The synthesis of mitochondrial DNA (mDNA) in HeLa cells is selectively inhibited by relatively low concentrations of ethidium bromide. After exposure of cells to strongly inhibitory concentrations of the drug, the apparent superhelix density of mDNA is rapidly increased, as judged by its buoyant density in CsCl in the presence of ethidium bromide. Mitochondrial DNA synthesized in the presence of partially inhibitory concentrations of ethidium bromide is also altered in its buoyant density in the presence of the dye, but is more heterogeneous in this respect. However, the change in buoyant density of newly synthesized mDNA may be explained by changes in structure other than a change in superhelix density, as indicated by its increased resistance to digestion by pancreatic DNase.     

POPULATION STRUCTURE AND MORPH-SPECIFIC FITNESS DIFFERENCES IN TRISTYLOUS LYTHRUM SALICARIA

In tristylous plant populations, style-morph frequencies are governed by an interaction between frequency-dependent selection due to disassortative mating and stochastic processes. Provided that there are no inherent fitness differences among morphs, frequency-dependent selection should result in equal morph frequencies at equilibrium. Stochastic models indicate that the short-styled morph has the highest and the long-styled morph the lowest probability of being lost from local populations as a result of random processes. We surveyed the morph composition of 82 populations of the tristylous, self-incompatible herb Lythrum salicaria in two archipelagos, one in central and one in northern Sweden, located close to the range-margin of the species. To examine whether deviations from even morph frequencies can be explained by among-morph differences in reproductive success, we quantified flower and seed production in six and three populations in the northern and southern archipelago, respectively, and we recorded segregation ratios in offspring produced in six trimorphic populations in the northern area. Seed germination and offspring growth were studied in the greenhouse. Ninety percent of the populations in the southern archipelago (N = 31) and 69% of the populations in the northern archipelago (N = 35) were trimorphic; the remaining populations were dimorphic (only populations consisting of at least three flowering plants considered). Dimorphic populations were smaller than trimorphic populations, as predicted by stochastic models. There was a striking difference in the morph composition of L. salicaria populations between the two archipelagos. In the southern archipelago, there was a slight excess of the long-styled morph and a corresponding deficiency of the short-styled morph. In contrast, the northern populations were characterized by a marked deficiency of the mid-styled morph: the average frequency of the mid-styled morph in trimorphic populations was 0.21, and nine of eleven dimorphic populations lacked the mid-styled morph. In both archipelagos, the long-styled morph (the most common morph) produced about 20% fewer seeds per fruit than the other morphs. The long-styled morph also tended to produce fewer seeds per plant. A hand-pollination experiment performed in two of the northern populations indicated that seed production per flower was pollen-limited in the long-styled morph but not in the other two morphs. Seed germination and offspring size after 24 weeks of growth did not differ among morphs. The mid-styled morph tended to have a higher representation in the offspring than in the parental generation in all six trimorphic populations studied further indicating that the deficiency of the mid-styled morph in the northern archipelago does not represent an equilibrium. Taken together, the results do not support the hypothesis that morph-specific differences in reproductive success can account for deviations from even morph frequencies in L. salicaria. It is suggested that among-morph differences in other components of fitness and historical factors may contribute to the current morph structure.     

鸮形目8种鸟类线粒体DNA多态性研究

采用14种限制性内切酶,对鸮形目8种鸟类(Tyto alba、T.capensis、Otus bakkamoena、O.scops、Asio otus、A.flammeus、Strix aluco、Glaucidium cuculoides)线粒体DNA进行限制性片段长度多态分析, 结果表明:不同种间存在基因组长度多态性,短耳鸮为23.35 kb,长耳鸮为19.78 kb,斑头鸺鹠为18.62 kb,红角鸮为17.65 kb.鸮形目种间具有较高的遗传变异,其中仓鸮和草鸮的平均遗传距离为1.0%,长耳鸮和短耳鸮平均为10.8%,红角鸮和领角鸮平均为13.1%,灰林鸮和斑头鸺鹠为12.3%,其中红角鸮与斑头鸺鹠的平均遗传距离最大为17.5%.鸮形目鸟类线粒体DNA的进化速率为每百万年变化2.0%～2.2%,提示鸮形目两个科间在距今2 800～3 000万年前分歧开来,同时,鸱鸮科各种间的分歧时间在距今2 000～2 500万年前,即处于中新世中期.     

GEOGRAPHIC VARIATION AND HETEROCHRONY IN TWO SPECIES OF COWRIES (GENUS CYPRAEA)

Geographic variation in the marine, Indo-Pacific cowry, Cypraea caputserpentis, involves clinal variations that parallel the ontogenetic development of adult shell characteristics. Cypraea caputdraconis, a closely related species endemic to Easter Island and Sala y Gómez, is morphologically similar to juvenile C. caputserpentis. Using multivariate measures of size and shape, I examine these patterns as a possible outcome of heterochrony, or changes in the timing of developmental events in ontogeny. Whorl-expansion rates of juvenile shells are significantly higher in C. caputdraconis when compared to C. caputserpentis and are negatively correlated with surface seawater temperatures among populations of C caputserpentis. High expansion rates, often associated with slow growth, result in a delay in the onset of lateral callus development and subsequent paedomorphosis. Ontogenetic trajectories calculated from growth series of adult and preadult shells indicate that paedomorphosis results from the combined effects of neoteny and post-displacement. Paedomorphosis among cowries may result from the advantages of larger body size relative to shell size under reduced predation intensities and associated increases in fecundity.     

形目8种鸟类线粒体DNA多态性研究

采用１４种限制性内切酶,对号鸟形目８种鸟类（Ｔｙｔｏａｌｂａ、Ｔｃａｐｅｎｓｉｓ、Ｏｔｕｓｂａｋｋａｍｏｅｎａ、Ｏｓｃｏｐｓ、Ａｓｉｏｏｔｕｓ、Ａｆｌａｍｍｅｕｓ、Ｓｔｒｉｘａｌｕｃｏ、Ｇｌａｕｃｉｄｉｕｍｃｕｃｕｌｏｉｄｅｓ）线粒体ＤＮＡ进行限制性片段长度多态分析,结果表明：不同种间存在基因组长度多态性,短耳号鸟为２３３５ｋｂ,长耳号鸟为１９７８ｋｂ,斑头鸺留鸟为１８６２ｋｂ,红角号鸟为１７６５ｋｂ。号鸟形目种间具有较高的遗传变异,其中仓号鸟和草号鸟的平均遗传距离为１０％,长耳号鸟和短耳号鸟平均为１０８％,红角号鸟和领角号鸟平均为１３１％,灰林号鸟和斑头鸺留鸟为１２３％,其中红角号鸟与斑头鸺留鸟的平均遗传距离最大为１７５％。号鸟形目鸟类线粒体ＤＮＡ的进化速率为每百万年变化２０％～２２％,提示号鸟形目两个科间在距今２８００～３０００万年前分歧开来,同时,鸱号鸟科各种间的分歧时间在距今２０００～２５００万年前,即处于中新世中期。     

POPULATION STRUCTURE OF THE BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) AS DETERMINED BY RESTRICTION ENDONUCLEASE ANALYSIS OF MITOCHONDRIAL DNA

Abstract: Restriction fragment length polymorphisms of mitochondrial DNA (mtDNA) were used to test for population subdivision in the bottlenose dolphin (Tursiops truncatus). Atlantic and Pacific dolphin mtDNA samples exhibited distinctly different haplotypes (approximately 2.4% sequence divergence), indicating a lack of gene exchange. Within the Atlantic Ocean, mtDNA samples from the Gulf of Mexico and the Atlantic Coast were also found to be distinct, with a sequence divergence of approximately 0.6%. The Atlantic Coast–Gulf of Mexico dichotomy is consistent with patterns of genetic variation from other marine and coastal organisms from this region, and supports the hypothesized role of bio-geographic events in promoting the divergence of these and other forms. Regional differentiation was identified along the Atlantic Coast, whereas low sequence divergences among haplotypes and consistent haplotype frequencies across populations suggested considerable gene exchange among Gulf of Mexico populations. A highly divergent haplotype found in two individuals from two localities in the Gulf of Mexico is best explained by dispersal from either a distinct offshore Gulf stock or an unsampled Atlantic Coast stock. Additional samples are required to test for the existence of a distinct offshore race and, if it exists, to identify its distribution and contribution to population structure.     

MICROGEOGRAPHIC VARIATION IN MITOCHONDRIAL DNA OF MEADOW VOLES (MICROTUS PENNSYLVANICUS) IN RELATION TO POPULATION DENSITY

We examined mitochondrial-DNA (mtDNA) sequence heterogeneity on four adjacent trapping grids in an island population of meadow voles (Microtus pennsylvanicus) at two different population densities. Four restriction endonucleases revealed 20 different mtDNA composite phenotypes in samples totaling 198 meadow voles. There were significant heterogeneities in the distribution of four common mtDNA composite phenotypes among the four trapping grids, suggesting that there is population subdivision on a fine scale. Genetic distances between grids, mtDNA diversity within grids, and G_ST also varied during the study period. We found a decrease in genetic distance and an increase in diversity when the population density was high and vice versa when the population density was low. When population density was high, the coefficient of gene differentiation was smaller than the same coefficient observed when the population density was low. These changes in population subdivision and diversity are consistent with theoretical expectations of population structure in which effective female population size and dispersal are the critical variables. The data also support the hypothesis of maintenance of mtDNA diversity by population subdivision, rapid population growth rate, and dispersal.     

COMPARISON OF POPULATION STRUCTURE IN CHROMOSOMALLY POLYTYPIC AND MONOTYPIC SPECIES OF SCELOPORUS (SAURIA: IGUANIDAE) IN RELATION TO CHROMOSOMALLY-MEDIATED SPECIATION

Sceloporus grammicus has been used as an example of stasipatric speciation, and some models of chromosomal speciation have assumed that the fission rearrangements which distinguish the chromosome races within this complex are negatively heterotic in the heterozygous state. Consequently, such rearrangements are assumed to be fixed by drift in small, inbred populations. Allelic variation at 19 presumptive gene loci was examined in 13 samples of a chromosomally conservative congener, Sceloporus graciosus, and was compared to an equivalent data set for the chromosomally polytypic S. grammicus. Several estimates of population variability and structure were calculated, and results were inconsistent with models of extreme population subdivision and/or frequent bottlenecks and extinction-colonization events in S. grammicus. For example, mean level of heterozygosity and mean number of alleles per locus were significantly higher in S. grammicus than in S. graciosus, while the average genetic distance (D) was significantly higher in S. graciosus. These results are considered in light of expected “Wrightian” population genetic parameters, and we conclude that S. grammicus does not seem to have the population structure necessary for the fixation of strongly negatively heterotic rearrangements.     

POPULATION DIFFERENCES IN INDIGENOUS FUSARIUM SPECIES BY CORN CULTURE OF PRAIRIE SOIL

Six species of Fusarium were identified among approximately 7,000 cultures isolated from roots and soils collected from prairies and cornfields in southern Minnesota. In both soil sources, F. oxysporum and F. solani predominated, followed in order by F. roseum, F. episphaeria, F. tricinctum, and F. moniliforme. The same order was obtained for the 28 species of prairie grasses and forbs as for corn. From prairie plant and corn roots, respectively, F. oxysporum was isolated from 64 and 90%; F. solani, 26 and 80%; F. roseum, 8 and 35%; and F. tricinctum, 6 % each. In 10 of 17 companion soil pairs, populations of Fusarium species were higher in cornfield than in prairie soils. Populations of F. roseum and F. moniliforme especially, were higher in cornfield soils of sample pairs, but populations of F. solani were higher in prairie soils. Fusarium roseum ‘Equiseti’ was the predominant cultivar of this species in both prairie and cornfield soils. Thus all six species of Fusarium appeared to be indigenous to the prairie, and some, especially F. roseum, apparently had increased in prevalence in soil and roots by corn culture.     

TEMPORAL CHANGE OF MITOCHONDRIAL DNA HAPLOTYPE FREQUENCIES AND FEMALE EFFECTIVE SIZE IN A BROWN TROUT (SALMO TRUTTA) POPULATION

We report data on genetic drift of mitochondrial DNA (mtDNA) haplotypes in a natural brown trout (Salmo trutta) population in Sweden. Large temporal frequency shifts were observed over the 14 consecutive year classes studied. The observed rate of drift was used to estimate the effective size of the population. This effective size applies to the female segment of the population as mtDNA is maternally inherited. The magnitude of mtDNA haplotype frequency change is compared with the corresponding allele frequency changes at 14 allozyme loci in the same population. The female effective size is estimated as 58, which is approximately half the effective size of 97 for the total population (both sexes) previously obtained from the shifts of allozyme allele frequencies.     

ARE CHLOROPLAST AND MITOCHONDRIAL DNA VARIATION SPECIES INDEPENDENT IN OAKS?

Extensive introgression of cytoplasmic genomes across oak species is now a well-established fact. To distinguish between ancient hybridization events and ongoing introgression, a direct test for the existence of local exchanges is proposed. Such local exchanges must be comparatively recent, that is, contemporaneous with or later than the last postglacial recolonization. The test is applied to an extensive set of data comprising 377 pure or mixed populations (1744 individuals) of four white oak species in southern France. After demonstrating that local exchanges have occurred frequently between all species pairs, another test is performed to check if species status does nevertheless play some role in restricting cytoplasmic gene flow. The results vary according to the species pairs considered, and the observed pattern may be related to the ecology and/or compatibility of interspecific crosses. It is also shown that, for some of these oak species, the presence of related species in a population significantly influences the intraspecific diversity. Altogether, the results demonstrate that (1) intraspecific cytoplasmic gene flow varies according to the species, (2) interspecific cytoplasmic gene flow varies according to the species pair, and (3) both components of gene flow are at least partly related.     

PHYLOGEOGRAPHIC STRUCTURE IN MITOCHONDRIAL DNA OF THE LAKE WHITEFISH (COREGONUS CLUPEAFORMIS) AND ITS RELATION TO PLEISTOCENE GLACIATIONS

Restriction-fragment length polymorphisms were employed to evaluate the phylogenetic relationships, the genetic diversity and the geographic structure in mitochondrial DNA (mtDNA) lineages of the lake whitefish, Coregonus clupeaformis. Thirteen restriction enzymes that produced 148 restriction fragments were used to assay mtDNAs of 525 specimens collected among 41 populations. The sampling covered the entire range of the species, from Alaska to Labrador. Four distinct phylogeographic assemblages were identified. The Beringian assemblage, confined to Yukon and Alaska, was phylogenetically distinct from other assemblages and exhibited the highest level of nucleotide diversity. The Acadian assemblage was confined to southeastern North America and composed of a unique mtDNA clade. The Atlantic assemblage was confined to southern Québec and the northeastern United States and was also observed among anadromous populations of northern Hudson Bay. This group was highly polymorphic and responsible for most of the mtDNA diversity observed outside Beringia. The Mississippian assemblage occupied most of the actual range of lake whitefish, from the Mackenzie delta to Labrador. Ninety-two percent of all whitefish of this proposed origin belonged to a single mtDNA haplotype. Overall, the diversity, the geographic structure and the times of divergence of mtDNA phylogenetic assemblages correlate with the Pleistocene glaciations classically assumed to have dramatically altered the genetic diversity of northern fishes in recent evolutionary times. Our results emphasize the dominant role of these catastrophic events in shaping the population genetic structure of lake whitefish.     

DIFFERENTIATION OF MITOCHONDRIAL DNA POLYMORPHISMS IN POPULATIONS OF FIVE JAPANESE ABIES SPECIES

Mitochondrial DNA polymorphism of 40 populations of five Abies species was investigated using PCR-amplified coxI and coxIII gene probes. Using four combinations of probe and restriction enzyme, we detected three major haplotypes and 15 total haplotypes. We also found varied levels of gene diversity for the different species: 0.741, 0.604, 0.039, 0.000, and 0.292 for A. firma, A. homolepis, A. veitchii, A. mariesii, and A. sachalinensis, respectively. The marginal and southern populations of A. firma and A. homolepis have unique haplotypes, especially the Kyushu, Shikoku, and Kii Peninsula populations, which inhabit areas coinciding with probable refugia of the last glacial period and possess high levels of mtDNA genetic diversity. The haplotypes in some populations suggested mtDNA capture also occurred between species through introgression/hybridization. The strong mtDNA population differentiation in Abies is most likely due to the maternal inheritance of mitochondria and restricted seed dispersal. A phenetic tree based on the genetic similarity of the mtDNA suggests that some species are polyphyletic. Based on mtDNA variation, the five Abies species could be divided roughly into three groups: (1) A. firma and A. homolepis, (2) A. veitchii and A. sachalinensis, and (3) A. mariesii. However, we found that all these Abies species, except A. mariesii, are genetically very closely related according to an analysis of their cpDNA sequences. This showed that the chloroplast rbcL gene differed by only one base substitutions among the four species. We believe that the mtDNA variation and cpDNA similarity clearly reflect relationships among, and the dissemination processes affecting these Abies species since the last glacial period.