bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between population genetic structure and riparian habitat as revealed by RAPD analysis of the rheophyte Acorus gramineus Soland. (Araceae) in Taiwan
Authors: LIAO L. C. , HSIAO J. Y.
Published: March 2003

Acorus gramineus Soland. (Araceae) is a rheophyte and is distributed in southeastern Asia. Its populations are restricted to riparian habitats. The discontinuous distribution might result in high genetic diversification among plants of different river systems. In the present study, leaf samples were collected from populations along six river systems in western Taiwan and the genetic variation was investigated by employing RAPD markers. A total of 255 samples from 17 sampling sites was studied. Eighty random 10‐mer primers were screened and six of them, which showed better amplification results, were selected to analyse all of the samples. Data of 34 high‐intensity and highly reproducible polymorphic fragments were used in statistical analyses. The results of AMOVA analyses indicated that, of the total variation, 46.84% was attributable to differences among river systems, 16.88% to differences among sampling sites within river systems, and 36.28% to differences among individuals within sampling sites. The results of cluster analysis and principal coordinate analysis revealed that sampling sites of each river system formed distinct clusters and the sampling sites of six river systems were clustered into three main groups according to latitudinal relationships. The results of the present study indicated that the population genetic structure of the plants of different river systems is highly diversified, which seems to imply that the gene flow among them is very limited.
Evidence for transfer of antibiotic‐resistance genes in soil populations of streptomycetes
Authors: WIENER P. , EGAN S. , WELLINGTON E. M. H.
Published: March 2003

Phylogenetic analysis was used to evaluate the hypothesis of gene transfer in streptomycetes, many of which are antibiotic producers. The diversity and possible origins of streptomycin‐resistance genes was investigated for a population of Streptomyces strains isolated from a site in Brazil where antibiotic production had previously been implicated. The analysis provides compelling evidence for the transfer of these genes. Examination of other Streptomyces‐type strains also reveals a scattered distribution of streptomycin producers with respect to the overall phylogeny. These results suggest that horizontal gene transfer may be an important factor in the evolution of antibiotic genes in streptomycetes.
A preliminary examination of genetic variation in a peripheral population of Blanding's turtle,Emydoidea blandingii
Authors: MOCKFORD S. W. , SNYDER M. , HERMAN T. B.
Published: March 2003

Random amplified polymorphic DNA (RAPD) was used to compare the Nova Scotia population of Blanding's turtle (Emydoidea blandingii) with several populations from the species’ main range. The Nova Scotia population is believed to have been isolated from the main range for 4000–8000 years. Cluster analysis using a neighbour‐joining algorithm produced a dendrogram showing the Nova Scotia population clustering separately from those populations in the main range. Analysis of molecular variance shows 34.28% of total variance to be accounted for between the Nova Scotia population and populations in the main range. While this study is preliminary, the results suggest that the Nova Scotia population of Blanding's turtle may be important to the maintenance of genetic diversity in the species.
The postglacial history of Scots pine (Pinus sylvestris L.) in western Europe: evidence from mitochondrial DNA variation
Authors: Sinclair W. T. , Morman J. D. , Ennos R. A.
Published: March 2003

The geographical structure of mitochondrial (mt)DNA variants (mitotypes) was investigated in 38 western European populations of Scots pine Pinus sylvestris using restriction fragment length polymorphism (RFLP) analysis of total DNA and a homologous cox1 probe. Three major mitotypes (designated a, b and d) were detected. Within Spain all three major mitotypes were found, gene diversity was high, HT = 0.586, and this diversity was distributed predominantly among rather than within populations (FST(M) = 0.813 for the seven Spanish populations). Mitotype d was present only in the most southerly population from the Sierra Nevada. Elsewhere in Europe, populations showed little or no mtDNA diversity within regions, but there were marked differences between regions. Italian populations were fixed for mitotype b; populations from northern France, Germany, Poland, Russia and southern Sweden were fixed for mitotype a; while populations in northern Fennoscandia were fixed for mitotype b. The isolated Scottish populations were predominantly of mitotype a, but mitotype b was present in three of the 20 populations scored. In Scotland, UK gene diversity (HT = 0.120) and genetic differentiation among populations (FST(M) = 0.37) was much lower than in Spain. When interpreted in the light of complementary data from pollen analysis and nuclear genetic markers, the results suggest that present‐day populations of P. sylvestris in western Europe have been derived from at least three different sources after glaciation.
An analysis of the distribution of juvenile Atlantic salmon (Salmo salar) in nature as a function of relatedness using microsatellites
Authors: FONTAINE P.‐M. , DODSON J. J.
Published: March 2003

The major objective of this study was to test the hypothesis that juvenile Atlantic salmon kin occupy adjacent territories in their natural habitat in order to profit from the benefits associated with kin‐biased behaviours, as has been observed under controlled laboratory conditions. Microsatellites were used to establish the relatedness of salmon fry (in their first summer of life) and parr (in their second and third summer of life) captured in adjacent territories. We did not observe a relationship between the proximity and the relatedness of either parr of the same cohort or fry in their natural habitat. Although many pairs of fry were identified as being related when sampled immediately after emergence, most family groups did not occupy adjacent territories. The high dispersal potential in rivers, the low occupation rate of the habitat and the incidence of half‐sibs in nature most probably reduce the opportunity and advantage of kin‐biased behaviour, in contrast to laboratory studies conducted in artificial, high‐density conditions.
Molecular variation inLeymusspecies and populations
Authors: ANAMTHAWAT‐JÓNSSON K. , BRAGASON B. TH. , BÖDVARSDÓTTIR S. K. , KOEBNER And R. M. D.
Published: March 2003

Icelandic populations of European lymegrass [Leymus arenarius(L.) Hochst.] were examined using amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) of the major ribosomal genes (18S–5.8S–26S rDNA), in comparison with Alaskan populations of its closely related speciesL. mollis(Trin.) Pilger. The AFLP profiles emerged as two distinct entities, clearly separating the two species, and based on species‐specific bands it was simple to distinguish these two morphologically similar species. The rDNA–RFLPs also differentiated the species. Within species, the IcelandicL. arenariuswas more homogeneous than the AlaskanL. mollis, and its variation was dispersed over geographically different populations, suggesting a common gene pool. The variation among the AlaskanL. molliswas more extensive and its interrupted pattern may be the result of gene introgression at subspecies level. Within a 40‐year‐old population ofL. mollisestablished in Iceland from Alaskan material, the molecular profiles separated old and new genotypes. Both AFLP and rDNA revealed the new genotypes to be extremely similar. This rapid change in allele frequency is thought to be the result of adaptation to a new environment.
Molecular diversity of arbuscular mycorrhizal fungi colonising Hyacinthoides non‐scripta (bluebell) in a seminatural woodland
Authors: Helgason T. , Fitter A. H. , Young J. P. W.
Published: March 2003

Arbuscular mycorrhizal (AM) fungi form symbiotic associations with plant roots. Around 150 species have been described and it is becoming clear that many of these species have different functional properties. The species diversity of AM fungi actively growing in roots is therefore an important component of ecosystem diversity. However, it is difficult to identify AM fungi below the genus level from morphology in planta, as they possess few informative characters. We present here a molecular method for identifying infrageneric sequence types that estimate the taxonomic diversity of AM fungi present in actively growing roots. Bluebell roots were sampled from beneath two different canopy types, oak and sycamore, and DNA sequences were amplified from roots by the polymerase chain reaction with fungal‐specific primers for part of the small subunit ribosomal RNA gene. Restriction fragment length polymorphism among 141 clones was assessed and 62 clones were sequenced. When aligned, discrete sequence groups emerged that cluster into the three families of AM fungi: Acaulosporaceae, Gigasporaceae and Glomaceae. The sequence variation is consistent with rRNA secondary structure. The same sequence types were found at both sampling times. Frequencies of Scutellospora increased in December, and Acaulospora increased in abundance in July. Sites with a sycamore canopy show a reduced abundance of Acaulospora, and those with oak showed a reduced abundance of Glomus. These distribution patterns are consistent with previous morphological studies carried out in this woodland. The molecular method provides an alternative method of estimating the distribution and abundance of AM fungi, and has the potential to provide greater resolution at the infrageneric level.
Phylogeography and postglacial colonization routes of Ips typographus L. (Coleoptera, Scolytidae)
Authors: Stauffer  , Lakatos  , Hewitt
Published: March 2003

Ips typographus populations were analysed by enzyme electrophoresis and by sequence analysis in order to quantify the degree of population differentiation. Enzyme electrophoresis showed a high gene flow among all European populations. Analysis of single loci showed that aspartate aminotransferase‐2 (Aat‐2) clustered the Scandinavian populations apart from the other populations whereas other enzyme loci showed no significant pattern. Analysis of mitochondrial DNA revealed eight haplotypes. The populations from Italy, Croatia and Belgium were the most polymorphic. Two haplotypes (I and II) were found in the majority of Central European populations. In the northern populations only one haplotype (I) was found. The Russian and Lithuanian populations had a particular haplotype (IV) that was not found in any of the other populations. In view of these data it is suggested that the population structure of I. typographus has been influenced by events which took place during and after the last ice age. Populations were forced into refugial areas in the south and in the area north of Moscow along with the host tree, Picea abies. P. abies had four refugial areas: the Apennine Alps, the Dinaric Alps, the Carpathian Alps and Kostroma, an area north of Moscow. With amelioration of the temperature, beetles spread after P. abies. According to the data presented here, I. typographus migrated from the Apennine and/or Dinaric Alps to the north. Whilst there is evidence for high gene flow among populations, bottleneck effects can still be detected in the north and also in the east. Beetles from the refugial area north of Moscow did not spread to Scandinavia or to the west like the host tree.
Kin cohesiveness and possible inbreeding in the mouthbrooding tilapia Sarotherodon melanotheron (Pisces Cichlidae)
Authors: Pouyaud  , Desmarais  , Chenuil  , Agnese  , Bonhomme
Published: March 2003

Four microsatellite markers were used to study genetic variation among individuals of the mouthbrooding tilapia Sarotherodon melanotheron (Rüppel 1852) caught in separate but adjacent shoals. A comparison was also made with fish from six other localities. Populations originating from riverine environments appear to be panmictic, while samples from open waters such as lagoons showed highly significant heterozygote deficiencies. For instance, at the 33‐allele locus SMEL4, 32 homozygous individuals were observed among the 82 individuals from the same lagoon location instead of only five homozygotes expected if random mating occurred. A further assessment of the genetic similarity of individuals within each shoal, validated by robust permutation techniques requiring no precise knowledge of gene frequencies, showed that related individuals tend to aggregate, and suggested that mating occurs preferentially within small groups of kin. Cichlids are often presented as a group of fish where microallopatric speciation takes place. The possible link between kin aggregation, inbreeding and shoaling behaviour we propose here may have important consequences for our understanding of the mechanisms involved in this fast speciation process.
Nuclear ribosomal DNA (nrDNA) concerted evolution in natural and artificial hybrids of Armeria (Plumbaginaceae)
Authors: Fuertes Aguilar J. , Rosselló J. A. , Nieto Feliner G.
Published: March 2003

Nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) sequences from artificial hybrids and backcrosses between Armeria villosa ssp. longiaristata and A. colorata were studied to assess the possible effects of concerted evolution in natural hybrids. F1 artificial hybrids show the expected pattern of additive polymorphisms for five of the six variable sites as estimated from direct sequences. However, homogenization of polymorphism is already observed in the F2, and is biased towards A. colorata except for one site. In backcrosses, an expected tendency towards homogenization of polymorphic sites in the direction of the recurrent parent is observed for five sites, although this does not necessarily imply concerted evolution. Conversely, the sixth site appears to elude such a mechanism and thus provides additional support for the occurrence of biased concerted evolution. Our findings are relevant to interpreting phylogeographic patterns involving gene flow and are also consistent with the hypothesis of a hybrid origin of A. villosa ssp. carratracensis.
Suppression of randomly primed polymerase chain reaction products (random amplified polymorphic DNA) in heterozygous diploids
Authors: Reineke A. , Karlovsky P. , Zebitz C. P. W.
Published: March 2003

In a study of genetic polymorphism in the gypsy moth Lymantria dispar we observed the aberrant inheritance of a random amplified polymorphic DNA (RAPD) fragment designated H11‐589. This fragment was present in amplification products of F1 progeny of different crosses although it was not amplified from either parental DNA. DNA‐mixing experiments revealed that the presence of DNA containing a template for another product (H11‐746), amplified with the same primer, suppressed the synthesis of H11‐589. The templates for both RAPD products were highly repetitive and scattered throughout the L. dispar genome. Southern hybridization and sequence analysis of H11‐746 and H11‐589 revealed an extensive sequence homology and an internal repetitive motif of 17 nucleotides present in both products. Interactions between templates for H11‐746 and H11‐589 are expected to occur during the polymerase chain reaction (PCR), offering an explanation for the suppression of the amplification of H11‐589. The role of the internal repetitive motif and of the copy number of both templates in the suppression effect are discussed. Our results corroborate doubts regarding the suitability of the RAPD technique for quantitative genetic analysis, in particular where mixed populations are concerned.
Colonization history and introduction dynamics ofCapsella bursa‐pastoris(Brassicaceae) in North America: isozymes and quantitative traits
Authors: Neuffer B. , Hurka H.
Published: March 2003

Multilocus isozyme genotypic composition for aspartate aminotransferase (AAT), leucine aminopeptidase (LAP) and glutamate dehydrogenase (GDH) was studied forCapsellain the source continent, Europe (9000 plants from 593 populations), and in the colonized continent, North America (2700 plants from 88 populations). North America was depauperate in the number of genotypes (by ≈ 50%), but in terms of frequencies, a few genotypes were common and shared by both continents. Although some, very rare, genotypes were, however, unique for North America, our data provided no evidence to indicate that the introduced gene pools were reconstructed on a multilocus genetic basis after introduction. Instead, they argued for a considerable number of independent introduction events. Geographical distribution patterns of multilocus genotypes in Europe and North America were pronounced and enabled us to trace the colonization history of CalifornianCapsellaback to Spanish ancestral populations and those of temperate North America back to temperate European gene pools. A random‐block field experiment with 14 Californian populations from different climatic regions revealed that variation patterns of quantitative traits reflect ecotypic variation, and the ecological amplitude ofCapsellain North America is similar to that in Europe, which can be traced back to the introduction of preadapted genotypes. It appears that certain multilocus isozyme genotypes are associated with certain ecotypes. The variable European gene pool ofCapsellawas essentially introduced into North America without major genetic changes.
DNA fingerprinting data and the analysis of population genetic structure by comparing band‐sharing patterns
Authors: Bertorelle G. , Bucchini L. , Pilastro A. , Matessi C.
Published: March 2003

Genetic isolation among populations can be effectively investigated by multilocus DNA fingerprinting. If populations have diverged, it is expected that the mean proportion of bands shared by individuals from the same population, Bw, exceeds the corresponding mean, Bb, calculated from pairs of individuals from distinct populations. A problem arises in deciding whether any difference between Bw and Bb is statistically significant. In fact, any two band‐sharing data (bij), contributing to Bw or Bb, are not independent if they share a common individual (like bij and bjl). This prevents a correct application of parametric tests, such as the Student’s t‐test. Recently, a modification of this test has been proposed that should avoid the independence problem. Using a large number of samples of fingerprints, simulated from an appropriate ‘genetic’ model, under a wide range of conditions, we compared the performances of the Student’s t‐test, the modified t‐test and five new permutation tests, where individuals, rather than bij values, are permuted. We found that: (i) the Student’s t‐test can be very permissive, rejecting too often the null hypothesis when true, but is correct or conservative in certain cases; (ii) the modified t‐test is extremely conservative when the null hypothesis is true and very inefficient otherwise; (iii) all five permutation tests are strictly correct, provided that individuals are ordered randomly on gels; and (iv) in this case, the permutation tests are equally efficient, and are not inferior to the Student’s t‐test when the latter is approximately correct and provides a fair benchmark.
An examination of hybridization between the cattail speciesTypha latifoliaandTypha angustifoliausing random amplified polymorphic DNA and chloroplast DNA markers
Authors: Kuehn M. Marcinko , Minor J. E. , White B. N.
Published: March 2003

Typha glaucarepresents a significant portion of the biomass of the wetlands surrounding the Great Lakes, USA. It is generally accepted to be a form of hybrid betweenT. latifoliaandT. angustifolia, which itself appears to be an exotic introduction from Europe. Based on morphological and isozyme data, conflicting theories have been proposed for the hybrid nature ofT. glauca: it has been described as a hybrid swarm, a distinct hybrid species and an F1hybrid. Therefore, we developed random amplified polymorphic DNA (RAPD) and chloroplast DNA markers, specific to the parental species, to assess hybrids. Ten RAPD primers gave 17 fragments specific toT. angustifoliaand 13 fragments specific toT. latifolia. All of the interspecific hybrids contained each of the species‐specific markers, indicating an F1hybrid status. Furthermore, all hybrids tested contained theT. angustifoliachloroplast haplotype, which is consistent with differential interspecific crossing success found previously. Additional confirmation of an F1hybrid status was gained by examining seedlings fromT. glauca. These progeny were expected to be advanced‐generation hybrids, as opposed to the F1hybrid parent. Analysis of the seedlings revealed segregating marker patterns consistent with patterns observed in experimental advanced‐generation hybrids, although these advanced hybrids do not appear to be a significant part of mature stands. Our data do not provide support for extensive gene flow betweenT. latifoliaandT. angustifolia. However, our results suggest that hybridization between the native and introducedTyphaspecies has impacted the native population through the spread of the F1hybrid,T. glauca.
Wild relatives and crop cultivars: detecting natural introgression and farmer selection of new genetic combinations in agroecosystems
Authors: Jarvis Devra I. , Hodgkin Toby
Published: March 2003

Whether new combinations of genes that result from hybridization and introgression between wild and cultivated taxa are maintained, with the resultant development of populations with new characteristics, depends on natural selection, and in the case of crops, on human selection. While many cases of deliberate introgression of desirable traits into crop cultivars as part of breeding programmes are known, the extent and significance of natural or farmer‐assisted introgression is uncertain. A range of techniques have been used to document natural hybridization and introgression of agricultural crops and their wild relatives in many crops including maize, wheat, barley, oats, pearl millet, foxtail millet, quinoa, hops, hemp, potato, cocona, casava, common bean, cowpea, pigeon pea, carrots, squash, tomato, radish, letuce, chilli, beets, sunflower, cabbage, and rasberries. However, the majority of these studies are based on morphological characters, and few have investigated the frequency with which such new types are produced and retained in natural and agroecosystems for farmer selection. Even more limited is information on the role of farmers in recognizing and selecting new genetic variation from the natural introgression of crops with their wild relatives, and the impact, once selected, of these new genetic combinations on the crop diversity. Molecular evaluation of natural introgression linked to investigations of farmer recognition and use of introgressed types provide ways of evaluating whether farmer selection for introgressed types is a significant process in increasing the genetic diversity of crop plants.
High genetic diversity in a population of the ectomycorrhizal basidiomycete Laccaria amethystina in a 150‐year‐old beech forest
Authors: Gherbi H. , Delaruelle C. , Selosse M.‐A. , Martin F.
Published: March 2003

The genetic structure of a population of the ectomycorrhizal basidiomycete Laccaria amethystina (Bolt. ex Hooker) Murr. was assessed in a closed 150‐year‐old beech (Fagus sylvatica L.) forest in the Vosges Mountains in northeastern France. During the autumn of 1994 and 1997, sporophores were collected from three 100‐m2 sampling plots located along a 120‐m transect crossing the beech stand. The genetic variation of 676 sporophores was initially estimated using heteroduplex analysis of the ribosomal DNA intergenic spacer (IGS1). Ten unique IGS1 heteroduplex/homoduplex patterns were identified, although three types represented most of the sporophores analysed. Each group of IGS1 type was then analysed using random amplified microsatellite analysis (RAMS). RAMS resolved 388 different genotypes amongst the 634 sporophores analysed from the three plots during the autumn of 1994 and 1997. Density as high as 130 genets per 100 m2 was observed during the autumn of 1994. The largest clone covered ≈ 1 m2, but most genets covered a few cm2 and produced only one to three sporophores. Only eight genotypes identified in 1994 were found in 1997. Although L. amethystina has the capacity for vegetative persistence, the present study indicates that its populations maintain a genetic structure more consistent with a high frequency of sexual reproduction. This suggests that beech trees could be recolonized by new genotypes each year. Alternatively, this spatial distribution may also arise from erratic fruiting of underground persistent genets. These features (i.e. numerous genets of small size), typical of ruderal species, contrast with studies carried out on other ectomycorrhizal basidiomycetes occurring in mature closed forests.
Patterns of genetic variation in native grape phylloxera on two sympatric host species
Authors: Downie D. A.
Published: March 2003

Random amplified polymorphic DNA (RAPD) markers were used to examine population genetic structure in populations of native grape phylloxera. This research asked: (i) do RAPD markers distinguish two groups corresponding to the two host plant species; and (ii) do RAPD markers distinguish groups according to spatial location, independent of host plant association? Forty‐nine phylloxera clones were collected from five pairs of adjacent individuals of two sympatric grape species in five sites along a 145 km transect in Missouri, USA. A high level of polymorphism was observed, with some evidence for structuring between host plant species and no evidence for spatial structuring. An analysis of molecular variance (amova) found that 6.52% of the variance in RAPD banding patterns was attributable to host species and 7.96% of the variance was attributable to spatial location. A cluster analysis did not result in two groups corresponding to the two hosts, or to five groups corresponding to the geographical sites sampled. A Mantel test showed a low correlation between genetic similarity and spatial location. Two of the 93 RAPD markers were nonrandomly associated between the hosts. It is suggested that there may be a small host‐mediated effect on genetic variation but stochastic dispersal and a highly heterogeneous environment may be the primary influences on the observed polymorphism.
The linkage disequilibrium between chloroplast DNA and mitochondrial DNA haplotypes in Beta vulgaris ssp. maritima (L.): the usefulness of both genomes for population genetic studies
Authors: Desplanque B. , Viard F. , Bernard J. , Forcioli D. , Saumitou‐Laprade P. , Cuguen J. , Van Dijk H.
Published: March 2003

The structure and evolution of the plant mitochondrial genome may allow recurrent appearance of the same mitochondrial variants in different populations. Whether the same mitochondrial variant is distributed by migration or appears recurrently by mutation (creating homoplasy) in different populations is an important question with regard to the use of these markers for population genetic analyses. The genetic association observed between chloroplasts and mitochondria (i.e. two maternally inherited cytoplasmic genomes) may indicate whether or not homoplasy occurs in the mitochondrial genome. Four‐hundred and fourteen individuals sampled in wild populations of beets from France and Spain were screened for their mitochondrial and chloroplast polymorphisms. Mitochondrial DNA (mtDNA) polymorphism was investigated with restriction fragment length polymorphism (RFLP) and chloroplast DNA (cpDNA) polymorphism was investigated with polymerase chain reaction PCR–RFLP, using universal primers for the amplification. Twenty and 13 variants for mtDNA and cpDNA were observed, respectively. Most exhibited a widespread geographical distribution. As a very strong linkage disequilibrium was estimated between mtDNA and cpDNA haplotypes, a high rate of recurrent mutation was excluded for the mitochondrial genome of beets. Identical mitochondrial variants found in populations of different regions probably occurred as a result of migration. We concluded from this study that mtDNA is a tool as valuable as cpDNA when a maternal marker is needed for population genetics analyses in beet on a large regional scale.
Phylogeography of the pitviper clade Agkistrodon: historical ecology, species status, and conservation of cantils
Authors: Parkinson Christopher L. , Zamudio Kelly R. , Greene Harry W.
Published: March 2003

We used mitochondrial DNA sequences from three gene regions and two tRNAs (ND4, tRNA‐HIS‐SER, 12S, and 16S rDNA) to investigate the historical ecology of the New World pitviper clade Agkistrodon, with emphasis on the disjunct subspecies of the cantil, A. bilineatus. We found strong evidence that the copperhead (A. contortrix) is basal to its congeners, and that the cottonmouth (A. piscivorus) is basal to cantils. Phylogeography and natural history of the living terminal taxa imply that Agkistrodon primitively occupied relatively temperate habitats, with subsequent evolution of tropicality in ancestral A. bilineatus. Our best supported phylogeny rejects three gulf arc scenarios for the biogeography of A. bilineatus. We find significant statistical support for an initial divergence between populations on the east and west coasts of México and subsequent occupancy of the Yucatán Peninsula, by way of subhumid corridors in northern Central America. Based on phylogenetic relationships, morphological and molecular divergence, and allopatry we elevate A. b. taylori of northeastern México to species status. Taylor’s cantil is likely threatened by habitat destruction and small geographical range, and we offer recommendations for its conservation and management.
Allochronic speciation, secondary contact, and reproductive character displacement in periodical cicadas (Hemiptera:Magicicadaspp.): genetic, morphological, and behavioural evidence
Authors: Cooley John R. , Simon Chris , Marshall David C. , Slon Karen , Ehrhardt Christopher
Published: March 2003

Periodical cicadas have proven useful in testing a variety of ecological and evolutionary hypotheses because of their unusual life history, extraordinary abundance, and wide geographical range. Periodical cicadas provide the best examples of synchronous periodicity and predator satiation in the animal kingdom, and are excellent illustrations of habitat partitioning (by the three morphologically distinct species groups), incipient species (the year classes or broods), and cryptic species (a newly discovered 13‐year species,Magicicada neotredecim). They are particularly useful for exploring questions regarding speciation via temporal isolation, or allochronic speciation. Recently, data were presented that provided strong support for an instance of allochronic speciation by life‐cycle switching. This speciation event resulted in the formation of a new 13‐year species from a 17‐year species and led to secondary contact between two formerly separated lineages, one represented by the new 13‐year cicadas (and their 17‐year ancestors), and the other represented by the pre‐existing 13‐year cicadas. Allozyme frequency data, mitochondrial DNA (mtDNA), and abdominal colour were shown to be correlated genetic markers supporting the life‐cycle switching/allochronic speciation hypothesis. In addition, a striking pattern of reproductive character displacement in male call pitch and female pitch preference between the two 13‐year species was discovered. In this paper we report a strong association between calling song pitch and mtDNA haplotype for 101 individuals from a single locality within theM. tredecim/M. neotredecimcontact zone and a strong association between abdomen colour and mtDNA haplotype. We conclude by reviewing proposed mechanisms for allochronic speciation and reproductive character displacement.
Colony kin structure and male production inDolichovespulawasps
Authors: Foster Kevin R. , Ratnieks Francis L. W. , Gyllenstrand Niclas , Thorén Peter A.
Published: March 2003

In annual hymenopteran societies headed by a single outbred queen, paternity (determined by queen mating frequency and sperm use) is the sole variable affecting colony kin structure and is therefore a key predictor of colony reproductive characteristics. Here we investigate paternity and male production in five species ofDolichovespulawasps. Twenty workers from each of 10 colonies of each of five species, 1000 workers in total, were analysed at three DNA microsatellite loci to estimate paternity. To examine the relationship between kin structure and reproductive behaviour, worker ovary activation was assessed by dissection and the maternal origin of adult males was assessed by DNA microsatellites. Effective paternity was low in all species (D.media1.08,D. maculata1.0,D. sylvestris1.15,D. norwegica1.08 andD. saxonica1.35), leading to the prediction of queen–worker conflict over male production. In support of this, workers with full‐size eggs in their ovaries (four out of five species) and adult males that were workers’ sons (all five species) were found in queenright colonies. However, workers were only responsible for a minority of male production (D.media7.4%,D. maculata20.9%,D. sylvestris9.8%,D. norwegica2.6% andD. saxonica34.6%) suggesting that the queen maintains considerable reproductive power over the workers. Kin structure and reproductive conflict inDolichovespulacontrast with their sister groupVespula.Dolichovespulais characterized by low paternity, worker reproduction, and queen–worker conflict andVespulaby high paternity, effective worker policing and absence of worker reproduction. The trend revealed by this comparison is as predicted by kin selection theory suggesting that colony kin structure has been pivotal in the evolution of the yellowjacket wasps.
Sex‐biased dispersal and a density‐independent mating system in the Australian brushtail possum, as revealed by minisatellite DNA profiling
Authors: Ji W. , Sarre S. D. , Aitken N. , Hankin R. K. S. , Clout M. N.
Published: March 2003

Natal dispersal can have important effects on mammal population structure and dynamics following a local population crash. Such dispersal is of practical importance when applied to the control of pest species because dispersal may significantly, and undesirably, reduce the population recovery time following a control operation. The relative dispersal rate of the sexes is also critical because that too will affect the rate of population increase. Here, we describe a field experiment in which we reduce the density of two populations of the Australian brushtail possum, and use genetic similarity, as estimated by minisatellite DNA profiles, to investigate dispersal in the original (undisturbed) and recovering populations. Our results show that the genetic similarity within the undisturbed populations was lower between males than between females. Conversely, the genetic similarities between males and females in the two recovering populations were not significantly different, while relatedness among males was significantly higher in the recovering populations when compared with those in the pre‐removal populations. These data indicate two important characteristics of dispersal in possums: (i) that dispersal in established populations is sex biased towards males; and (ii) that within the first 3 years following population control, ‘the vacuum effect’, whereby individuals from areas adjacent to a control area expand their home range and invade the depopulated area, is the most important factor in the re‐colonization process for possums. We found no evidence that the mating system, which is polygynous, varied when the density was markedly reduced. These results indicate that drastic reductions in population density by conventional control will not affect the rate of spread of biological control agents that rely on sexual transmission for dissemination.
Phylogeography of endemic ermine (Mustela erminea) in southeast Alaska
Authors: Fleming Melissa A. , Cook Joseph A.
Published: March 2003

The North Pacific Coast (NPC) of North America is a region of high mammalian endemism, possibly due to its highly fragmented landscape and complex glacial history. For example, four island and one mainland subspecies of ermine,Mustela erminea, have been described as endemic to southeast Alaska alone. To better understand the role of past climatic change in generating diversity in the region, we examined DNA sequence variation in the mitochondrial cytochrome b gene of 210 ermine from across North America, with an emphasis on Alaska and British Columbia. We found three distinct (1.5–3.6% uncorrected ‘p’) lineages of ermine, all of which occur in southeast Alaska. One lineage includes a southeast Alaska endemic and specimens from Alaska (outside of southeast) and Eurasia. A second lineage includes two southeast Alaskan endemics and ermine from western Canada and the coterminous United States. The close relationships of these purported endemics to ermine outside of southeast Alaska suggest that they colonized the region from Beringian and southern glacial refugia, respectively, following deglaciation of the NPC. The third lineage appears restricted to the Prince of Wales Island complex in southeast Alaska (two subspecies) and Graham Island (Haida Gwaii), British Columbia. This restricted distribution suggests that these populations may be derived from relicts that persisted in a coastal refugium during the Wisconsin glaciation. Studies of nuclear genes and adaptive morphological evolution are necessary to further explore discrepancies between the geographical pattern of differentiation based on mtDNA and the existing subspecific taxonomy based on morphology.
Comparative phylogeography of sympatric sister species, Clevelandia ios and Eucyclogobius newberryi (Teleostei, Gobiidae), across the California Transition Zone
Authors: Dawson M. N , Louie K. D. , Barlow M. , Jacobs D. K. , Swift C. C.
Published: March 2003

It is paradigmatic in marine species that greater dispersal ability often, but not always, results in greater gene flow and less population structure. Some of the exceptions may be attributable to studies confounded by comparison of species with dissimilar evolutionary histories, i.e. co‐occurring species that are not closely related or species that are closely related but allopatric. Investigation of sympatric sister species, in contrast, should allow differences in phylogeographic structure to be attributed reliably to recently derived differences in dispersal ability. Here, using mitochondrial DNA control region sequence, we first confirm that Clevelandia ios and Eucyclogobius newberryi are sympatric sister taxa, then demonstrate considerably shallower phylogeographic structure in C. ios than in E. newberryi. This shallower phylogeographic structure is consistent with the higher dispersal ability of C. ios, which most likely results from the interaction of habitat and life‐history differences between the species. We suggest that the paradigm will be investigated most rigorously by similar studies of other sympatric sister species, appended by thorough ecological studies, and by extending this sister‐taxon approach to comparative phylogeographic studies of monophyletic clades of sympatric species.
Recent introduction of the dominant tunicate,Pyura praeputialis(Urochordata, Pyuridae) to Antofagasta, Chile
Authors: Castilla J. C. , Collins A. G. , Meyer C. P. , Guiñez R. , Lindberg D. R.
Published: March 2003

The large sessile tunicatePyura stolonifera(Pleurogona: Stolibranchiata: Pyuridae), has been regarded as a complex taxon with disjointed distributions, including Australia (Pyura stolonifera praeputialis), South Africa (Pyura stolonifera stolonifera) and South America (Chile, Antofagasta:Pyurasp., the ‘piure de Antofagasta’), and has been cited under at least five taxonomic combinations. The ‘piure de Antofagasta’ is a competitively dominant species in rocky intertidal habitats and shows a limited geographical range (60–70 km) exclusively inside the Bay of Antofagasta. Using cytochrome oxidase I (COI) mitochondrial sequence data fromPyuraspecimens of the three taxa we tested whether the Chilean taxon represents: (i) a Gondwana relict; (ii) a more recently divergent species; or (iii) a recently introduced species. The results suggest that the Chilean taxon is a recent introduction to Chile from Australian populations and thatPyura stolonifera praeputialis, from Australia, and the ‘piure de Antofagasta’ are geographical populations of a single species:Pyura praeputialis; whereas the South African taxon represents a second species:Pyura stolonifera.
Landscape scale genetic effects of habitat fragmentation on a high gene flow species: Speyeria idalia (Nymphalidae)
Authors: Williams Barry L. , Brawn Jeffrey D. , Paige Ken N.
Published: March 2003

Detection of the genetic effects of recent habitat fragmentation in natural populations can be a difficult task, especially for high gene flow species. Previous analyses of mitochondrial DNA data from across the current range of Speyeria idalia indicated that the species exhibited high levels of gene flow among populations, with the exception of an isolated population in the eastern portion of its range. However, some populations are found on isolated habitat patches, which were recently separated from one another by large expanses of uninhabitable terrain, in the form of row crop agriculture. The goal of this study was to compare levels of genetic differentiation and diversity among populations found in relatively continuous habitat to populations in both recently and historically isolated habitat. Four microsatellite loci were used to genotype over 300 individuals from five populations in continuous habitat, five populations in recently fragmented habitat, and one historically isolated population. Results from the historically isolated population were concordant with previous analyses and suggest significant differentiation. Also, microsatellite data were consistent with the genetic effects of habitat fragmentation for the recently isolated populations, in the form of increased differentiation and decreased genetic diversity when compared to nonfragmented populations. These results suggest that given the appropriate control populations, microsatellite markers can be used to detect the effects of recent habitat fragmentation in natural populations, even at a large geographical scale in high gene flow species.
PepA, a secreted protein of Pseudomonas aeruginosa, is necessary for cytotoxicity and virulence
Authors: Hauser Alan R. , Kang Pil Jung , Engel Joanne N.
Published: March 2003

Pseudomonas aeruginosa is an opportunistic pathogen and a leading cause of hospital‐acquired pneumonia. We identified a 73 kDa protein, designated Pseudomonas exoprotein A (PepA), that was secreted by P. aeruginosa strain PA103. PepA was necessary for in vitro killing of epithelial cells as well as virulence in a mouse model of acute pneumonia. Several properties of PepA suggested that it was secreted by a type III system. Secretion occurred without cleavage of a signal peptide and in low‐calcium environments in the presence of a divalent cation chelator, as is the case for characterized P. aeruginosa type III secreted proteins. Secretion of PepA was absent from isogenic mutants with defective type III pathways. Finally, amino‐terminal peptide sequence analysis indicated that the amino‐terminal five residues of PepA were identical to those of ExoS and ExoT, two type III secreted proteins of P. aeruginosa. After secretion, PepA underwent cleavage at two sites, each with the sequence A–X–K–S, suggesting that the cleavage may be caused by a protease. The gene encoding PepA, designated pepA, was cloned and sequenced, and comparisons with the genetic database using BLAST alignments indicated that the nucleotide sequence of pepA and the inferred protein sequence of PepA had no homology to known sequences. A nucleotide sequence identical to the consensus element for binding of ExsA, a transcriptional activator of P. aeruginosa type III secretion genes, was located 84 bp 5′ of the translational start codon. Analysis of transposon insertion mutants indicated that the carboxy terminus was required for cytotoxicity. Examination of respiratory clinical isolates demonstrated that pepA was a variable trait and probably acquired by horizontal transmission. Consistent with this hypothesis was the identification of a putative insertion element 94 bp 5′ of the PepA translational start site. Analysis of G + C content of the PepA coding sequence and the adjacent insertion element suggested that they were acquired together from a different species. In summary, PepA is a secreted protein of P. aeruginosa that is necessary for epithelial cell cytotoxicity in vitro and virulence in a mouse model of pneumonia.
Chemotactic response regulator mutant CheY95IV exhibits enhanced binding to the flagellar switch and phosphorylation‐dependent constitutive signalling
Authors: Schuster Martin , Abouhamad Walid N. , Silversmith Ruth E. , Bourret Robert B.
Published: March 2003

CheY, a response regulator protein in bacterial chemotaxis, mediates swimming behaviour through interaction with the flagellar switch protein, FliM. In its active, phosphorylated state, CheY binds to the motor switch complex and induces a change from counterclockwise (CCW) to clockwise (CW) flagellar rotation. The conformation of a conserved aromatic residue, tyrosine 106, has been proposed to play an important role in this signalling process. Here, we show that an isoleucine to valine substitution in CheY at position 95 — in close proximity to residue 106 — results in an extremely CW, hyperactive phenotype that is dependent on phosphorylation. Further biochemical characterization of this mutant protein revealed phosphorylation and dephosphorylation rates that were indistinguishable from those of wild‐type CheY. CheY95IV, however, exhibited an increased binding affinity to FliM. Taken together, these results show for the first time a correlation between enhanced switch binding and constitutive signalling in bacterial chemotaxis. Considering present structural information, we also propose possible models for the role of residue 95 in the mechanism of CheY signal transduction.
Schizosaccharomyces pombe isp4 encodes a transporter representing a novel family of oligopeptide transporters
Authors: Lubkowitz Mark A. , Barnes David , Breslav Michael , Burchfield Aaron , Naider Fred , Becker Jeffrey M.
Published: March 2003

We have recently cloned an oligopeptide transport gene from Candida albicans denoted OPT1. This gene showed significant sequence similarity to three open reading frames (ORFs) with no previously established function: isp4 from Schizosaccharomyces pombe and Saccharomyces cerevisiae YJL212C and YPR194C, identified during the genome project. The S. pombe gene isp4 was originally identified by Sato et al. as a gene that was upregulated through nitrogen starvation induction of meiosis. However, an isp4Δ strain exhibited a wild‐type phenotype with respect to sexual differentiation. We have found that the same isp4Δ strain is deficient in tetrapeptide transport activity as measured by its resistance to toxic tetrapeptides, by its inability to accumulate a radiolabelled tetrapeptide and by the inability to use tetrapeptides as a sole source of an amino acid to satisfy an auxotrophic requirement. Similarly, we found that the ORF YPR194C from S. cerevisiae encodes an oligopeptide transporter. Sequence analyses as well as physiological evidence has led us to propose that the proteins encoded by isp4 and the genes identified from S. cerevisiae and C. albicans comprise a new group of transporters specific for small oligopeptides, which we have named the OPT family.