bluuebunny/crossref_metadata_2025 huggingface dataset:
Population structure and biogeography of migratory freshwater fishes (Prochilodus: Characiformes) in major South American rivers
Authors: Sivasundar Arjun , Bermingham Eldredge , Ortí Guillermo
Published: March 2003

Mitochondrial DNA (mtDNA) sequences were used to infer the phylogenetic relationships ofProchilodusspecies in the Paraná, Amazonas, Orinoco, and Magdalena basins. Sequences of ATPase subunits 6 and 8 (total 840 bp) were obtained for 21Prochilodusspecimens from the four river systems. UsingSemaprochilodusas an outgroup, phylogenetic analyses showed that: (i) each river basin contains a monophyletic group of mtDNA lineages; and (ii) the branching order places Magdalena in a basal position with subsequent branching of Orinoco, Amazon and Paraná. The mitochondrial control region was sequenced for 26P. lineatus(from the Paraná basin) and six otherProchilodusspecimens from the Magdalena, Orinoco and Amazon. All 26 control region haplotypes were unique with sequence divergence ranging from 0.3 to 3.6%. The control region phylogeny is well resolved but phylogenetic structure is not associated with geography. For example, mtDNA haplotypes from the upper Paraná (Mogui Guassú) and the upper Bermejo, separated by at least 2600 km, have close genealogical ties. Phylogeographic analyses, including nested clade analysis, suggest high levels of gene flow within this basin.
How many species of cichlid fishes are there in African lakes?
Authors: Turner George F. , Seehausen Ole , Knight Mairi E. , Allender Charlotte J. , Robinson Rosanna L.
Published: March 2003

The endemic cichlid fishes of Lakes Malawi, Tanganyika and Victoria are textbook examples of explosive speciation and adaptive radiation, and their study promises to yield important insights into these processes. Accurate estimates of species richness of lineages in these lakes, and elsewhere, will be a necessary prerequisite for a thorough comparative analysis of the intrinsic and extrinsic factors influencing rates of diversification. This review presents recent findings on the discoveries of new species and species flocks and critically appraises the relevant evidence on species richness from recent studies of polymorphism and assortative mating, generally using behavioural and molecular methods. Within the haplochromines, the most species‐rich lineage, there are few reported cases of postzygotic isolation, and these are generally among allopatric taxa that are likely to have diverged a relatively long time in the past. However, many taxa, including many which occur sympatrically and do not interbreed in nature, produce viable, fertile hybrids. Prezygotic barriers are more important, and persist in laboratory conditions in which environmental factors have been controlled, indicating the primary importance of direct mate preferences. Studies to date indicate that estimates of alpha (within‐site) diversity appear to be robust. Although within‐species colour polymorphisms are common, these have been taken into account in previous estimates of species richness. However, overall estimates of species richness in Lakes Malawi and Victoria are heavily dependent on the assignation of species status to allopatric populations differing in male colour. Appropriate methods for testing the specific status of allopatric cichlid taxa are reviewed and preliminary results presented.
Plague dynamics and population genetics of the desert locust: can turnover during recession maintain population genetic structure?
Authors: Ibrahim Kamal M.
Published: March 2003

The desert locust (Schistocerca gregaria) undergoes crowding‐induced phase transformation from solitary form to gregarious form. The transformations involves changes in behaviour, colour, development, morphometry, fecundity and endocrine physiology. Recession populations of the desert locust exist primarily in the solitary phase as small populations in patchy environments and are prone to extinction because of climatic events. Significant genetic differentiation among recession populations along the Red Sea coast of Eritrea was previously reported. It was hypothesized that despite the mixing effect of recurrent swarms, metapopulation dynamics could have produced genetic divergence among these highly scattered recession populations. A Monte Carlo simulation of the population dynamics of the desert locust in a metapopulation setting, with a realistic range of parameter values clearly demonstrated that this is possible. Population growth was represented by a discrete‐time logistic equation. The duration of recessions and swarms was sampled from normal distributions whose means and standard deviations were varied based on reported estimates. An average recession duration of 10 ± 3 generations and swarm periods half as long but almost twice as variable produced a partitioning of the total genetic variance most similar to that in the empirical study. In conventional metapopulation analysis, whether turnover leads to increased or reduced divergence is dependent on the number of colonists relative to the number of recurrent migrants, and on whether the colonists arise from a single patch or many patches. In the case of locusts, the stochastic boom and bust cycle is the overriding factor. Divergence between patches during recession due to founder effect and recurrent drift is balanced by the high rate of mixing during plagues.
Genetic diversity of Iberian populations of Bemisia tabaci (Hemiptera: Aleyrodidae) based on random amplified polymorphic DNA–polymerase chain reaction
Authors: Moya A. , Guirao P. , Cifuentes D. , Beitia F. , Cenis J. L.
Published: March 2003

The genetic structure of six Iberian populations of the whitefly Bemisia tabaci, two of them biotype Q, one biotype B, and the other three a mixture of both, has been studied using random amplified polymorphic DNA–polymerase chain reaction (RAPD–PCR). A total of 336 individuals was completely discriminated by means of 234 scored bands. Separate analyses of molecular variance of haploid males and diploid females using the pairwise number of differences between haplotypes showed that biotypes contribute significantly more to the observed variability than populations within biotypes. On average, gene flow between two biotypes of the same population is lower than between populations of identical biotypes. On the basis of these results and the nondetection under natural conditions of a single hybrid, we consider that both biotypes are genetically isolated under the ecological conditions prevailing in the south Iberian Peninsula. All populations of biotype Q presented similar values of intrapopulational diversity, which were higher than the values shown by populations of biotype B.
The impact of habitat fragmentation on dispersal of Cunningham’s skink (Egernia cunninghami): evidence from allelic and genotypic analyses of microsatellites
Authors: Stow A. J. , Sunnucks P. , Briscoe D. A. , Gardner M. G.
Published: March 2003

The effects of habitat fragmentation on processes within and among populations are important for conservation management. Despite a broad spectrum of lifestyles and the conservation significance of many reptiles, very little work on fine‐scale population genetics has been carried out on this group. This study examines the dispersal patterns of a rock crevice‐dwelling lizard, Cunningham’s skink (Egernia cunninghami), in a naturally vegetated reserve and an adjacent deforested site. Both genotypic and genic approaches were employed, using microsatellite loci. The spatial organization of individuals with respect to pairwise relatedness coefficients and allele frequencies, along with assignment tests, were used to infer dispersal characteristics for both sexes in a natural and a cleared area. The distribution of relatedness in both habitats was spatially structured, with E. cunninghami showing high pairwise relatedness within their rocky retreat sites. Analysis of relatedness over different spatial scales, spatial autocorrelation of alleles and assignment tests, all indicated that both sexes in the cleared area show less dispersal than their counterparts in the reserve. Furthermore, deforestation may inhibit female dispersal to a greater extent than that of males. The geographical structuring of allele frequencies for adults in the cleared area, but not the reserve, indicates that habitat fragmentation has the potential to alter at least the microevolution of E. cunninghami populations.
Population structure in two sympatric species of the Lake Tanganyika cichlid tribe Eretmodini: evidence for introgression
Authors: Rüber Lukas , Meyer Axel , Sturmbauer Christian , Verheyen Erik
Published: March 2003

Patterns of genetic differentiation were analysed and compared in two sympatric species of the endemic Lake Tanganyika cichlid tribe Eretmodini by means of mitochondrial DNA (mtDNA) sequences of the control region and six microsatellite DNA loci. The sample area covers a total of 138 km of mostly uninterrupted rocky shoreline in the Democratic Republic of Congo and includes the entire distribution range ofTanganicoduscf.irsacaethat stretches over a distance of 35 km. Both markers detected significant genetic differentiation within and between the two species.T.cf.irsacaecontained lower overall genetic variation thanEretmoduscyanostictus, possibly due to its more restricted range of distribution and its smaller effective population sizes. Complete fixation ofTanganicodusmtDNA haplotypes was observed inEretmodusat two localities, while at two other localities someTanganicodusindividuals possessedEretmodusmtDNA haplotypes. Taking into account the relatively large average sequence divergence of 6.2% between the two species, as well as the geographical distribution of mtDNA haplotypes in the lake, the observed pattern is more likely to be a consequence of asymmetric introgression than of shared ancestral polymorphism. As there is significant population differentiation between sympatricTanganicodusandEretmoduspopulations, the events of introgressions may have happened after secondary contact, but our data provide no evidence for ongoing gene flow and suggest that both species are reproductively isolated at present time.
Genetic diversity and structure of natural populations ofPlathymenia reticulata(Mimosoideae), a tropical tree from the Brazilian Cerrado
Authors: Lacerda D. R. , Acedo M. D. P. , Filho J. P. Lemos , Lovato M. B.
Published: March 2003

Plathymenia reticulatais a tropical tree native to the Brazilian Cerrado, one of the most important and endangered ecosystems in Brazil. This species presents high‐quality wood and potential for recovery of degraded areas. Despite its importance, almost nothing is known about its genetic or ecological features. Random amplified polymorphic DNA (RAPD) markers were used to investigate the genetic diversity and structure of six natural populations ofP. reticulata. DNAs from 117 adult individuals were amplified with 10 random primers and Shannon’s index andamovawere used to evaluate the levels of genetic diversity within and among populations. Through 72 markers, 70.8% of which were polymorphic, it was possible to obtain 117 unique RAPD phenotypes. The levels of genetic variability found in the six populations ofP. reticulatawere considerable and most of the genetic variation was found between individuals within populations, although pairwise ΦSTvalues indicated significant divergence between populations. The among‐population component accounted for, respectively, 12.3% and 16% of the genetic variation, according toamovaand Shannon’s index. These results were compared with other genetic studies on plant species and such a level of differentiation among populations corresponds to that which has usually been observed for outcrossing plants. The importance of maintenance of theP. reticulatapopulations and implications of the analysis of adult individuals, considering the longevity of this species and the relatively recent Cerrado fragmentation, are discussed.
Spatial analysis of allozyme and microsatellite DNA polymorphisms in the land snailHelix aspersa(Gastropoda: Helicidae)
Authors: Arnaud J.‐F. , Madec L. , Guiller A. , Bellido A.
Published: March 2003

The genetic structure of the land snailHelix aspersawas investigated for 21 populations collected along a road located in the polders of the Bay of Mont‐Saint‐Michel (Brittany, France), following a sampling scheme the area of which did not exceed 900 m in length. A total of 369 individuals were genotyped for five enzymatic markers and seven microsatellite loci. We used sequential hierarchicalF‐statistics at different spatial scales and spatial autocorrelation statistics to explore recent historical patterns involved in the observed genetic distribution. Whatever the statistics used, congruent levels of spatial genetic substructuring across loci were demonstrated, excepted for one allozyme locus. Overall spatial genetic arrangement matched in a substantial fashion theoretical predictions based on the limited dispersal power of land snails. Positive autocorrelation over short‐distance classes may result from the development of genetically distinct patches of individuals organized in family‐structured colonies. Therefore, spatial signatures of averageIcorrelograms can be viewed as the expression of a stepping‐stone model of population structure, sometimes involving external migrational events. Overall, the revealed pattern of population subdivision on a microgeographical scale was suggestive of a neighbourhood structure. Finally, microsatellite loci are especially suitable for the detection of small genetic clustering, and combining different classes of markers offers the potential to gain further insight into the description of spatial genetic variability over short temporal and geographical scales.
Genetic structure and distinctness of Apis mellifera L. populations from the Canary Islands
Authors: De La Rúa P. , Galián J. , Serrano J. , Moritz R. F. A.
Published: March 2003

The genetic structure of Apis mellifera populations from the Canary Islands has been assessed by mitochondrial (restriction fragment length polymorphisms of the intergenic transfer RNAleu‐COII region) and nuclear (microsatellites) studies. These populations show a low level of genetic variation in terms of average number of alleles and degree of heterozygosity. Significant differences in the distribution of alleles were found in both data sets, confirming the genetic differentiation among some of the islands but not within them. Two mitochondrial haplotypes characteristic of the Canary Islands are found at high frequencies, although populations are introgressed by imported honeybees of eastern European C lineage. This introgression is rather high on Tenerife and El Hierro and low on Gran Canaria and La Gomera, whereas on La Palma it has not been recorded. The finding of microsatellite alleles characteristic of the eastern European lineage corroborates the genetic introgression. Phylogenetic analyses indicate that the Canarian honeybees are differentiated from other lineages and provide genetic evidence of their African origin.
Diversity of endophytic fungi of single Norway spruce needles and their role as pioneer decomposers
Authors: Müller Michael M. , Valjakka Rauni , Suokko Aki , Hantula Jarkko
Published: March 2003

The diversity of endophytic fungi within single symptomless Norway spruce needles is described and their possible role as pioneer decomposers after needle detachment is investigated. The majority (90%) of all 182 isolates from green intact needles were identified as Lophodermium piceae. Up to 34 isolates were obtained from single needles. Generally, all isolates within single needles had distinct randomly amplified microsatellite (RAMS) patterns. Single trees may thus contain a higher number of L. piceae individuals than the number of their needles. To investigate the ability of needle endophytes to act as pioneer decomposers, surface‐sterilized needles were incubated on sterile sand inoculated with autoclaved or live spruce forest humus layer. The dry weight loss of 13–17% found in needles after a 20‐week incubation did not significantly differ between the sterilized and live treatments. Hence, fungi surviving the surface sterilization of needles can act as pioneer decomposers. A considerable portion of the needles remained green during the incubation. Brown and black needles, in which the weight loss had presumably taken place, were invaded throughout by single haplotypes different from L. piceae. Instead, Tiarasporella parca, a less common needle endophyte, occurred among these invaders of brown needles. Needle endophytes of Norway spruce seem thus to have different abilities to decompose host tissues after needle cast. L. piceae is obviously not an important pioneer decomposer of Norway spruce needles. The diversity of fungal individuals drops sharply when needles start to decompose. Thus, in single needles the decomposing mycota is considerably less diverse than the endophytic mycota.
Extreme specificity in epiparasitic Monotropoideae (Ericaceae): widespread phylogenetic and geographical structure
Authors: Bidartondo M. I. , Bruns T. D.
Published: March 2003

The Monotropoideae (Ericaceae) are nonphotosynthetic plants that obtain fixed carbon from their fungal mycorrhizal associates. To infer the evolutionary history of this symbiosis we identified both the plant and fungal lineages involved using a molecular phylogenetic approach to screen 331 plants, representing 10 of the 12 described species. For five species no prior molecular data were available; for three species we confirmed prior studies which used limited samples; for five species all previous reports are in conflict with our results, which are supported by sequence analysis of multiple samples and are consistent with the phylogenetic patterns of host plants. The phylogenetic patterns observed indicate that: (i) each of the 13 plant phylogenetic lineages identified is specialized to a different genus or species group within five families of ectomycorrhizal Basidiomycetes; (ii) mycorrhizal specificity is correlated with phylogeny; (iii) in sympatry, there is no overlap in mature plant fungal symbionts even if the fungi and the plants are closely related; and (iv) there are geographical patterns to specificity.
Phylogeographic analysis of the threatened and endangered superconglutinate‐producing mussels of the genus Lampsilis (Bivalvia: Unionidae)
Authors: Roe Kevin J. , Hartfield Paul D. , Lydeard Charles
Published: March 2003

Several species of freshwater unionid mussels in the genus Lampsilis exhibit a remarkable reproductive strategy. Female mussels of these species enclose their larvae in a minnow‐like lure, called a ‘superconglutinate’, to attract piscivorous fishes. When a fish attempts to ingest the superconglutinate the lure ruptures and the larvae are released to parasitize the fish. Of the four species of mussel which exhibit this strategy and are endemic to the Gulf Coast drainages of the southeastern United States, three are protected under the Endangered Species Act, and one is recognized as imperilled. Phylogenetic analysis of nucleotide sequences of the mitochondrial 16S ribosomal RNA and the first subunit of the cytochrome oxidase c genes was conducted on 18 individual specimens representing these four species and six outgroup taxa. Phylogenetic analyses of these data support the monophyly of the superconglutinate‐producing mussels, and indicates a strong geographical component to the data. The zoogeographic patterns of the four taxa included in the study are congruent with those seen in freshwater vertebrates, and are consistent with a vicariant pattern resulting from fluctuations in sea level during the Pleistocene. Despite the strong geographical structuring of the data, only one species, Lampsilis subangulata, was recovered as monophyletic. The authors attribute the lack of support for the monophyly of the remaining species to insufficient sequence variation and the recent origin of the ancestor of these taxa. Based on these data, any future captive breeding projects aimed at augmenting or re‐establishing populations should do so only from the appropriate source populations so as to maintain the genetic integrity of these nascent species.
A DNA test to sex ratite birds
Authors: Huynen Leon , Millar Craig D. , Lambert David M.
Published: March 2003

DNA‐based sex tests now exist for many avian species. However, none of these tests are widely applicable to ratites. We present DNA sequence data for a locus that is W chromosome‐linked in the kiwi, ostrich, cassowary, rhea, and emu. At the amino acid level, this sequence has significant homology to X‐linked genes in platyfish and Caenorhabditis elegans. Polymerase chain reaction (PCR) primers designed to this locus allow the assignment of sex in all species of living ratites.
Cross‐species infection of blood parasites between resident and migratory songbirds in Africa
Authors: Waldenström J. , Bensch S. , Kiboi S. , Hasselquist D. , Ottosson U.
Published: March 2003

We studied the phylogeny of avian haemosporidian parasites,HaemoproteusandPlasmodium, in a number of African resident and European migratory songbird species sampled during spring and autumn in northern Nigeria. The phylogeny of the parasites was constructed through sequencing part of their mitochondrial cytochrome bgene. We found eight parasite lineages, fiveHaemoproteusand threePlasmodium, infecting multiple host species. Thus, 44% of the 18 haemospiridian lineages found in this study were detected in more than one host species, indicating that host sharing is a more common feature than previously thought. Furthermore, one of thePlasmodiumlineages infected species from different host families, Sylviidae and Ploceidae, expressing exceptionally large host range. We mapped transmission events, e.g. the occurrence of the parasite lineages in resident bird species in Europe or Africa, onto a phylogenetic tree. This yielded three clades, twoPlasmodiumand oneHaemoproteus, in which transmission seems to occur solely in Africa. OnePlasmodiumclade showed European transmission, whereas the remaining twoHaemoproteusclades contained mixes of lineages of African, European or unknown transmission. The mix of areas of transmission in several branches of the phylogenetic tree suggests that transmission of haemosporidian parasites to songbirds has arisen repeatedly in Africa and Europe. Blood parasites could be viewed as a cost of migration, as migratory species in several cases were infected with parasite lineages from African resident species. This cost of migration could have considerable impact on the evolution of migration and patterns of winter distribution in migrating birds.
Influences of triploidy, parentage and genetic diversity on growth of the Pacific oysterCrassostrea gigasreared in contrasting natural environments
Authors: Garnier‐Géré Pauline Hélène , Naciri‐Graven Yamama , Bougrier Serge , Magoulas Antonios , Héral Maurice , Kotoulas Georgios , Hawkins Anthony , Gérard André
Published: March 2003

An increasing number of hypotheses are being proposed to explain the faster growth potential of triploids in molluscs, including their partial sterility or their higher heterozygosity compared to diploids. Triploid advantage however, remains controversial for poorer sites, because of a potential trade‐off with survival. These questions were addressed inCrassostrea gigasby deploying meiosis II triploids and their diploid siblings from a single mass spawning of three males and seven females, in two contrasting locations for their trophic resources. One hundred and fifty individuals were sampled at each site after nine months, measured for weight and biochemical composition, and genotyped using three microsatellite and seven allozyme loci. Higher performance was observed at the fast‐growing site for all traits except shell weight, and triploids had greater weights and biochemical contents than diploids at harvest. Triploids also grew faster at the poorer site, and showed similar survival rates to diploids at both sites. Triploids had significantly higher average allozyme and microsatellite diversity. However, they performed better for a wide range of individual heterozygosity values, arguing for an advantage of the triploid stateper se, that could be due to positive effects on growth of both sterility of triploids with subsequent resource re‐allocation and possible faster transcription with three copies of each gene. Despite evidence of very low or no inbreeding in the diploid sample, positive associations between individual allozyme diversity and growth were detected, which explained little but significant amounts of phenotypic variation. These associations were interpreted as direct effects of allozymes, either alone or including epistatic interactions with other loci. In addition, measures of individual distance (mean‐d2) specific to microsatellites, were negatively correlated with growth in diploids, indicating possible effects of outbreeding depression between more distant genomes of parents from distinct populations.
Arbuscular mycorrhizal community composition associated with two plant species in a grassland ecosystem
Authors: Vandenkoornhuyse P. , Husband R. , Daniell T. J. , Watson I. J. , Duck J. M. , Fitter A. H. , Young J. P. W.
Published: March 2003

Arbuscular mycorrhizal (AM) fungi are biotrophic symbionts colonizing about two‐thirds of land plant species and found in all ecosystems. They are of major importance in plant nutrient supply and their diversity is suggested to be an important determinant of plant community composition. The diversity of the AM fungal community composition in the roots of two plant species (Agrostis capillaris and Trifolium repens) that co‐occurred in the same grassland ecosystem was characterized using molecular techniques. We analysed the small subunit (SSU) ribosomal RNA gene amplified from a total root DNA extract using AM fungal‐specific primers. A total of 2001 cloned fragments from 47 root samples obtained on four dates were analysed by restriction fragment length polymorphism, and 121 of them were sequenced. The diversity found was high: a total of 24 different phylotypes (groups of phylogenetically related sequences) colonized the roots of the two host species. Phylogenetic analyses demonstrate that 19 of these phylotypes belonged to the Glomaceae, three to the Acaulosporaceae and two to the Gigasporaceae. Our study reveals clearly that the AM fungal community colonizing T. repens differed from that colonizing A. capillaris, providing evidence for AM fungal host preference. In addition, our results reveal dynamic changes in the AM fungal community through time.
Fitness of backcross six of hybrids between transgenic oilseed rape (Brassica napus) and wild radish (Raphanus raphanistrum)
Authors: Gueritaine G. , Sester M. , Eber F. , Chevre A. M. , Darmency H.
Published: March 2003

The process of introgression between a transgenic crop modified for better agronomic characters and a wild relative could lead potentially to increased weediness and adaptation to the environment of the wild species. However, the formation of hybrid and hybrid progeny could be associated with functional imbalance and low fitness, which reduces the risk of gene escape and establishment of the wild species in the field. Our work compares the fitness components of parents and different types of backcross in the sixth generation of hybrids between transgenic oilseed rape (Brassica napus, AACC, 2n = 38) resistant to the herbicide glufosinate and wild radish (Raphanus raphanistrum, RrRr, 2n = 18). The backcross with oilseed rape cytoplasm (OBC) has a fitness value 100 times lower than that of the backcross with wild radish cytoplasm (RBC). The herbicide‐resistant RBC has similar growth to the susceptible RBC, but final male and female fitness values are two times lower. In turn, susceptible RBC exhibit similar fitness to the control wild radishes. The relative fitnesses of the different types are the same whether or not they grow under competitive conditions. The consequence on fitness of the chromosome location of the transgene conferring resistance and the relevance of these results to the impact of gene flow on the environment are discussed.
Separating historic events from recurrent processes in cryptic species: phylogeography of mud snails (Hydrobia spp.)
Authors: Wilke T. , Pfenninger M.
Published: March 2003

The present study combines methods that were designed to infer intraspecific relationships (e.g. nested‐clade analysis (NCA), mismatch distributions and maximum likelihood gene flow analysis) to analyse historic events and recurrent processes in the cryptic mud snail species Hydrobia acuta and H. glyca. Specifically, we test the proposed allopatry of cryptic species and whether the peculiar range‐subdivision of the putative subspecies H. a. acuta and H. a. neglecta is a result of long‐distance dispersal or continuous range expansion. The NCA indicates a past fragmentation of the two H. acuta subspecies as well as past fragmentations within H. glyca. Gene‐flow analyses show extensive gene flow in an E–W direction (towards the Atlantic) in the Mediterranean H. a. acuta, generally low gene flow in a W–E direction in the Atlantic H. a. neglecta and complex gene‐flow pattern in a N–S but also in a S–N direction (against the Gulf Stream) in H. glyca. Based on these data and supportive ecological and oceanographical data, we hypothesize that the separation of the two H. acuta subspecies was not caused by long‐distance dispersal but by a range shift and/or range expansion of the closely related competitor H. glyca as a result of an interglacial warming with a subsequent range shift in H. acuta. Moreover, our data do not show evidence for a long‐term, stable sympatry of Hydrobia species, supporting the concept of allopatric relationships within cryptic radiations. NCA and gene‐flow analyses indicate that the only sympatric population found in our study is the result of a recent dispersal event from the nearby Mediterranean. It is assumed that allopatric relationships in ephemeral Hydrobia populations constitute an evolutionary advantage relative to competition, recruitment and re‐establishment of habitats. Mechanisms that could be of relevance for maintaining allopatry are discussed.
Population genetics of shortnose sturgeon Acipenser brevirostrum based on mitochondrial DNA control region sequences
Authors: Grunwald C. , Stabile J. , Waldman J. R. , Gross R. , Wirgin I.
Published: March 2003

Shortnose sturgeon is an anadromous North American acipenserid that since 1973 has been designated as federally endangered in US waters. Historically, shortnose sturgeon occurred in as many as 19 rivers from the St. John River, NB, to the St. Johns River, FL, and these populations ranged in census size from 101 to 104, but little is known of their population structure or levels of gene flow. We used the polymerase chain reaction (PCR) and direct sequence analysis of a 440 bp portion of the mitochondrial DNA (mtDNA) control region to address these issues and to compare haplotype diversity with population size. Twenty‐nine mtDNA nucleotide‐substitution haplotypes were revealed among 275 specimens from 11 rivers and estuaries. Additionally, mtDNA length variation (6 haplotypes) and heteroplasmy (2–5 haplotypes for some individuals) were found. Significant genetic differentiation (P < 0.05) of mtDNA nucleotide‐substitution haplotypes and length‐variant haplotypes was observed among populations from all rivers and estuaries surveyed with the exception of the Delaware River and Chesapeake Bay collections. Significant haplotype differentiation was even observed between samples from two rivers (Kennebec and Androscoggin) within the Kennebec River drainage. The absence of haplotype frequency differences between samples from the Delaware River and Chesapeake Bay reflects a probable current absence of spawning within the Chesapeake Bay system and immigration of fish from the adjoining Delaware River. Haplotypic diversity indices ranged between 0.817 and 0.641; no relationship (P > 0.05) was found between haplotype diversity and census size. Gene flow estimates among populations were often low (< 2.0), but were generally higher at the latitudinal extremes of their distribution. A moderate level of haplotype diversity and a high percentage (37.9%) of haplotypes unique to the northern, once‐glaciated region suggests that northern populations survived the Pleistocene in a northern refugium. Analysis of molecular variance best supported a five‐region hierarchical grouping of populations, but our results indicate that in almost all cases populations of shortnose sturgeon should be managed as separate units.
Extreme genetic differentiation among the remnant populations of marble trout (Salmo marmoratus) in Slovenia
Authors: Fumagalli L. , Snoj A. , Jesenšek D. , Balloux F. , Jug T. , Duron O. , Brossier F. , Crivelli A. J. , Berrebi P.
Published: March 2003

Populations of the marble trout (Salmo marmoratus) have declined critically due to introgression by brown trout (Salmo trutta) strains. In order to define strategies for long‐term conservation, we examined the genetic structure of the 8 known pure populations using 15 microsatellite loci. The analyses reveal extraordinarily strong genetic differentiation among populations separated by < 15 km, and extremely low levels of intrapopulation genetic variability. As natural recolonization seems highly unlikely, appropriate management and conservation strategies should comprise the reintroduction of pure populations from mixed stocks (translocation) to avoid further loss of genetic diversity.
A simulated annealing approach to define the genetic structure of populations
Authors: Dupanloup I. , Schneider S. , Excoffier L.
Published: March 2003

We present a new approach for defining groups of populations that are geographically homogeneous and maximally differentiated from each other. As a by‐product, it also leads to the identification of genetic barriers between these groups. The method is based on a simulated annealing procedure that aims to maximize the proportion of total genetic variance due to differences between groups of populations (spatial analysis of molecular variance;samova). Monte Carlo simulations were used to study the performance of our approach and, for comparison, the behaviour of the Monmonier algorithm, a procedure commonly used to identify zones of sharp genetic changes in a geographical area. Simulations showed that thesamovaalgorithm indeed finds maximally differentiated groups, which do not always correspond to the simulated group structure in the presence of isolation by distance, especially when data from a single locus are available. In this case, the Monmonier algorithm seems slightly better at finding predefined genetic barriers, but can often lead to the definition of groups of populations not differentiated genetically. Thesamovaalgorithm was then applied to a set of European roe deer populations examined for their mitochondrial DNA (mtDNA) HVRI diversity. The inferred genetic structure seemed to confirm the hypothesis that some Italian populations were recently reintroduced from a Balkanic stock, as well as the differentiation of groups of populations possibly due to the postglacial recolonization of Europe or the action of a specific barrier to gene flow.
Genetic mating system and the significance of harem associations in the bat Saccopteryx bilineata
Authors: Heckel Gerald , Von Helversen Otto
Published: March 2003

We analysed the polygynous mating system of the bat Saccopteryx bilineata using behaviour observations and genetic data on 11 microsatellite DNA loci. Basic social units in S. bilineata are harem groups that consist of single males and up to eight females. Colonies comprise several harem groups, and the composition of colonies and harems is often stable over several reproductive seasons. The combination of parentage exclusion and likelihood‐based parentage assignment in this study produced detailed parentage information for a large colony of S. bilineata. Reproduction occurred mostly within the colony (17% extra‐colony paternity), but social associations in harems within the colony did not represent reproductive units (70% extra‐harem paternity). The latter finding was consistent over three reproductive seasons. Spatial association of the roosting sites of males and females could not explain parentage patterns in the colony. Even though intra‐harem paternity was less frequent than expected, it contributed significantly to reproduction of harem males. On average, the number of offspring sired by a male with females in his harem territory increased significantly with harem size, which corresponds to the higher energetic investment that is related to the maintenance of large harems. However, extra‐harem paternity was not correlated with a male's harem size or intra‐harem reproductive success. This suggests that individual preferences of females rather than male traits associated with the ability to defend large harems are most likely to cause the detected differences between social association and genetic mating system.
Impact of oilseed rape expressing the insecticidal cysteine protease inhibitor oryzacystatin on the beneficial predator Harmonia axyridis (multicoloured Asian ladybeetle)
Authors: Ferry N. , Raemaekers R. J. M. , Majerus M. E. N. , Jouanin L. , Port G. , Gatehouse J. A. , Gatehouse A. M. R.
Published: March 2003

Insect‐resistant transgenic plants have been suggested to have deleterious effects on beneficial predators through transmission of the transgene product by the pest to the predator. To test this hypothesis, effects of oilseed rape expressing the cysteine protease inhibitor oryzacystatin‐1 (OC‐1) on the predatory ladybird Harmonia axyridis were investigated using diamondback moth Plutella xylostella as the pest species. As expected, oilseed rape expressing OC‐1 had no effects on either development or survival of the pest, which utilizes serine digestive proteases. Immunoassays confirmed accumulation of the transgene product in pest larval tissues at levels of up to 3 ng per gut. Characterization of proteolytic digestive enzymes of H. axyridis demonstrated that larvae and adults utilize cysteine and aspartic proteases; the former activity was completely inhibited by oryzacystatin in vitro. However, when H. axyridis larvae consumed prey reared on OC‐1 expressing plants over their entire life cycle, no significant effects upon survival or overall development were observed. The inhibitor initially stimulated development, with a shortening of the developmental period of the second instar by 27% (P < 0.0001) accompanied by a 36% increase in weight of second instar larvae (P = 0.007). OC‐1 had no detrimental effects on reproductive fitness of adult H. axyridis. Interestingly there was a significant increase in consumption of OC‐1 dosed prey. The results show that prey reared on transgenic plants expressing a protein which inhibited ladybird digestive enzymes in vitro had no effects in vivo; the ladybird was able to up‐regulate digestive proteases in response to the inhibitor.
Glacial refugia, haplotype distributions, and clonal richness of the Daphnia pulex complex in arctic Canada
Authors: Weider L. J. , Hobæk A.
Published: March 2003

As part of a large international Arctic biodiversity expedition (Tundra Northwest ′99), we examined the distribution of members of the arctic Daphnia pulex complex (Cladocera, Anomopoda) from 121 tundra ponds, spread across 16 sites spanning a large portion of arctic Canada (i.e. from 62°22′ N to 79°01′ N; 66°45′ W to 139°37′ W). Using allozyme electrophoresis and mitochondrial (mt)DNA analyses, we examined the population genetic (clonal) structure of these populations. The following taxa were detected in this complex: Daphnia pulicaria, D. middendorffiana and D. tenebrosa. Clear geographical differences in mean clonal richness and diversity were observed, with most western sites exhibiting higher clonal richness and diversity, than sites in the eastern Canadian Arctic. For both the pulicaria group (i.e. D. pulicaria and D. middendorffiana) and D. tenebrosa, the highest mean regional clonal richness was detected from the southern section of Banks Island, an unglaciated site situated on the edge or directly in the eastern fringe of the Beringian glacial refuge. A significant negative correlation was found between geographical distance from the Beringian edge, and overall regional clonal richness (i.e. sites closer to the edge harboured greater clonal richness). These results clearly indicate that more recently deglaciated regions (i.e. eastern Canadian Arctic) harbour lower levels of clonal richness than western regions nearer Beringia. We discuss the role that glacial refugia have played in influencing both biotic and genetic diversity in arctic taxa.
The fats of Escherichia coli during infancy and old age: regulation by global regulators, alarmones and lipid intermediates
Authors: DiRusso Concetta C. , Nyström Thomas
Published: March 2003

The fluidity and phase state of bacterial lipid bilayers commonly change in response to ambient environmental conditions to maintain the critical functions of the envelope as a semipermeable and selective boundary. A special, and intricate, set of alterations in membrane lipid metabolism is elicited by conditions causing growth arrest. Under such conditions, specific alterations in the membrane lipid–fatty acid composition are required for survival of the cell and, concurrently, the membrane lipids are suggested to serve as endogenous reserves providing carbon/energy for maintenance requirements. It appears that the global regulator FadR is required for both of these activities to be performed properly and that the FadR regulon is interconnected to the universal stress response of Escherichia coli. FadR, in conjuction with long‐chain fatty acyl‐CoA, long‐chain acyl‐ACP, ppGpp and cAMP, are key players in regulating the activities of enzymes and expression of genes involved in fatty acid and phospholipid metabolism in dividing and ageing E. coli cells.
Isolation and molecular characterization of a surface‐bound proteinase of Entamoeba histolytica
Authors: Jacobs Thomas , Bruchhaus Iris , Dandekar Thomas , Tannich Egbert , Leippe Matthias
Published: March 2003

Major pathogenic functions of Entamoeba histolytica involved in destruction of host tissues are the degradation of extracellular matrix proteins mediated by secreted cysteine proteinases and contact‐dependent killing of host cells via membrane‐active factors. A soluble protein with an affinity for membranes was purified from amoebic extracts to apparent homogeneity. N‐terminal sequencing and subsequent molecular cloning of the factor revealed that it is a member of the cysteine proteinase family of E. histolytica, which we termed CP5. Further experiments with the purified protein showed that it has potent proteolytic activity that is abrogated in the presence of inhibitors specific for cysteine proteinases. The enzyme firmly associates with membranes retaining its proteolytic activity and it produces cytopathic effects on cultured monolayers. A model of the three‐dimensional structure of CP5 revealed the presence of a hydrophobic patch that may account for the potential of the protein to associate with membranes. Immunocytochemical localization of the enzyme to the surface of the amoeba in combination with the recent finding that the gene encoding CP5 is missing in the closely related but non‐pathogenic Entamoeba dispar suggests a potential role of the protein in host tissue destruction of E. histolytica.
Anaerobic regulation of the Escherichia coli dmsABC operon requires the molybdate‐responsive regulator ModE
Authors: McNicholas Paul M. , Chiang Robin C. , Gunsalus Robert P.
Published: March 2003

Expression of the Escherichia coli dmsABC operon that encodes a molybdenum‐containing DMSO/TMAO reductase is increased in response to anaerobiosis and repressed by nitrate. These changes are mediated by the transcription factors Fnr and NarL respectively. Interestingly, modC strains that are defective in molybdate uptake exhibit impaired anaerobic induction and no nitrate‐dependent repression of the dmsABC operon. To determine if the molybdate‐responsive transcription factor ModE is involved in this process, a set of dmsA–lacZ operon fusions were constructed and analysed. The pattern of dmsA–lacZ expression in response to anaerobiosis and nitrate addition was identical in both modC and modE strains, thus suggesting a regulatory role for ModE. In vitro studies confirmed that ModE bound the dmsA promoter at a high‐affinity site typical of other E. coli ModE operator sites. Mutations in this site abolished ModE binding in vitro and displayed the same phenotype as a modE mutation. In contrast to previously characterized ModE operator sites, which either overlap or are located immediately upstream of the ModE‐regulated promoter, the ModE site is centred 52.5 bp downstream of the major dmsA transcript start site. We identified a putative integration host factor (IHF) binding site in the intervening sequence, and in vitro studies confirmed that IHF bound this site with high affinity. Using himA mutants, we confirmed that IHF plays a role in the molybdate‐dependent regulation of dmsA–lacZ expression in vivo. This study provides the first example in which ModE affects gene regulation in concert with another transcription factor.
Novel keto acid formate‐lyase and propionate kinase enzymes are components of an anaerobic pathway in Escherichia coli that degrades L‐threonine to propionate
Authors: Heßlinger Christian , Fairhurst Shirley A. , Sawers Gary
Published: March 2003

An immunological analysis of an Escherichia coli strain unable to synthesize the main pyruvate formate‐lyase enzyme Pfl revealed the existence of a weak, cross‐reacting 85 kDa polypeptide that exhibited the characteristic oxygen‐dependent fragmentation typical of a glycyl radical enzyme. Polypeptide fragmentation of this cross‐reacting species was shown to be dependent on Pfl activase. Cloning and sequence analysis of the gene encoding this protein revealed that it coded for a new enzyme, termed TdcE, which has 82% identity with Pfl. On the basis of RNA analyses, the tdcE gene was shown to be part of a large operon that included the tdcABC genes, encoding an anaerobic threonine dehydratase, tdcD, coding for a propionate kinase, tdcF, the function of which is unknown, and the tdcG gene, which encodes a L‐serine dehydratase. Expression of the tdcABCDEFG operon was strongly catabolite repressed. Enzyme studies showed that TdcE has both pyruvate formate‐lyase and 2‐ketobutyrate formate‐lyase activity, whereas the TdcD protein is a new propionate/acetate kinase. By monitoring culture supernatants from various mutants using 1H nuclear magnetic resonance (NMR), we followed the anaerobic conversion of L‐threonine to propionate. These studies confirmed that 2‐ketobutyrate, the product of threonine deamination, is converted in vivo by TdcE to propionyl‐CoA. These studies also revealed that Pfl and an as yet unidentified thiamine pyrophosphate‐dependent enzyme(s) can perform this reaction. Double null mutants deficient in phosphotransacetylase (Pta) and acetate kinase (AckA) or AckA and TdcD were unable to metabolize threonine to propionate, indicating that propionyl‐CoA and propionyl‐phosphate are intermediates in the pathway and that ATP is generated during the conversion of propionyl‐P to propionate by AckA or TdcD.