Cosmopolitan versus cryptic meiofaunal polychaete species: an approach to a molecular taxonomy

Polychaete taxonomy is characterised by a high number of apparently cosmopolitan species. Detection of subtle but diagnostic ultrastructural differences and – in recent years – investigations at the molecular level have revealed that many of these "species" are actually complexes of morphologically identical or almost identical cryptic species. To disregard their existence would lead to an underestimation of global meiofauna diversity and undermine the value of many scientific studies. Therefore, we strongly recommend that they be given formal taxonomic recognition, beyond their published presentation as "operational taxonomic units", "types" or by alphabetic or numerical designators. Since there are neither generally accepted practical procedures nor any established consensus regarding the application of genetic data in taxonomy, we here provide examples of, and suggestions for, the treatment of meiofaunal species that are distinguished exclusively by molecular data, e.g. by genetic distance values, cluster analyses, diagnostic (= autapomorphic) DNA fragments from DNA fingerprinting procedures (RAPD) and/or DNA sequence differences (e.g. of ITS 2). Although no holotype material may be available because the molecular procedures require the preparation of entire specimens, practical taxonomic problems can be overcome and the recommendations of the Zoological Code of Nomenclature satisfied, by adopting the following procedures: (1) deposition of band-patterns of an individual obtained with the primers used to find diagnostic markers; (2) deposition of DNA in ethanol of one syntype individual; (3) deposition of fixed specimens (syntypes) from the locus typicus. Electronic Publication     

Genetic Linkage Maps of Eucalyptus Grandis and Eucalyptus Urophylla Using a Pseudo-Testcross: Mapping Strategy and Rapd Markers

We have used a ``two-way pseudo-testcross' mapping strategy in combination with the random amplified polymorhic DNA (RAPD) assay to construct two moderate density genetic linkage maps for species of Eucalyptus. In the cross between two heterozygous individuals many single-dose RAPD markers will be heterozygous in one parent, null in the other and therefore segregate 1:1 in their F(1) progeny following a testcross configuration. Meiosis and gametic segregation in each individual can be directly and efficiently analyzed using RAPD markers. We screened 305 primers of arbitrary sequence, and selected 151 to amplify a total of 558 markers. These markers were grouped at LOD 5.0, θ = 0.25, resulting in the maternal Eucalyptus grandis map having a total of 240 markers into 14 linkage groups (1552 cM) and the paternal Eucalyptus urophylla map with 251 markers in 11 linkage groups (1101 cM) (n = 11 in Eucalyptus). Framework maps ordered with a likelihood support >/=1000:1 were assembled covering 95% of the estimated genome size in both individuals. Characterization of genome complexity of a sample of 48 mapped random amplified polymorphic DNA (RAPD) markers indicate that 53% amplify from low copy regions. These are the first reported high coverage linkage maps for any species of Eucalyptus and among the first for any hardwood tree species. We propose the combined use of RAPD markers and the pseudo-testcross configuration as a general strategy for the construction of single individual genetic linkage maps in outbred forest trees as well as in any highly heterozygous sexually reproducing living organism. A survey of the occurrence of RAPD markers in different individuals suggests that the pseudo-testcross/RAPD mapping strategy should also be efficient at the intraspecific level and increasingly so with crosses of genetically divergent individuals. The ability to quickly construct single-tree genetic linkage maps in any forest species opens the way for a shift from the paradigm of a species index map to the heterodox proposal of constructing several maps for individual trees of a population, therefore mitigating the problem of linkage equilibrium between marker and trait loci for the application of marker assisted strategies in tree breeding.     

Genetic diversity and species identification in the endangered white abalone (<Emphasis Type="Italic">Haliotis sorenseni</Emphasis>)

In 2001, the white abalone Haliotis sorenseni became the first marine invertebrate in United States waters to receive federal protection as an endangered species. Prior to the endangered species listing, 20 abalone were collected as potential broodstock for a captive rearing program. Using DNA from these animals, we have developed genetic markers, including five nuclear microsatellite loci and partial sequences of one nuclear (VERL) and two mitochondrial (COI and CytB) genes, to assess genetic variability in the species, aid in species identification, and potentially track the success of future outplanting of captive-reared animals. All five microsatellite loci were polymorphic and followed expectations of simple Mendelian inheritance in laboratory crosses. Each of the wild-caught adult abalone exhibited a unique composite microsatellite genotype, suggesting that significant genetic variation remains in natural populations. A combination of nuclear and mitochondrial gene sequencing demonstrated that one of the original wild-caught animals was, in fact, not a white abalone, but H. kamtschatkana (possibly subspecies assimilis). Similarly, another animal of uncertain identity accidentally collected by dredging was also shown to be H. kamtschatkana. Inclusion of these two animals as broodstock could have resulted in unintentional hybridizations detrimental to the white abalone recovery program. Molecular genetic identifications will be useful both in preventing broodstock contamination and as markers for future restocking operations.     

Genetic validation and characterization of RAPD markers differentiating black and red spruces: molecular certification of spruce trees and hybrids

 Picea mariana (black spruce) and P. rubens (red spruce) are closely related species which are difficult to differentiate morphologically. RAPD markers differentiating black and red spruces have been previously identified. In the present study, genetic validity of these markers was determined using samples representing range–wide provenances. Their applicability for certifying genetic identity of individual black, red trees and their hybrids from several sympatric and allopatric locations was demonstrated. These diagnostic fragments of both red and black spruce were present at a frequency of over 0.95 in allopatric provenances, but at a lower frequency in some sympatric provenances (0.43–1.00). Natural populations of red spruce exhibiting typical red spruce phenotype contained black spruce diagnostic RAPD fragments and black spruces growing in bogs with typical bog black spruce morphology, contained red spruce-specific RAPD markers. Some major RAPD markers were cloned and sequenced. The results reveal an extremely high degree of identity between the random primer and the primer binding sites on the genome. Amplification of black and red spruce genomic DNA with designed primers flanking the species-diagnostic RAPD markers indicates that most of RAPD markers used to differentiate black spruce from red spruce are not species specific since these sequences were detected in several spruce species using a more sensitive detection method. Received June 17, 2002; accepted August 5, 2002 Published online: February 4, 2003     

COI is better than 16S rRNA for DNA barcoding Asiatic salamanders (Amphibia: Caudata: Hynobiidae)

The 5' region of the mitochondrial DNA (mtDNA) gene cytochrome c oxidase I (COI) is the standard marker for DNA barcoding. However, because COI tends to be highly variable in amphibians, sequencing is often challenging. Consequently, another mtDNA gene, 16S rRNA gene, is often advocated for amphibian barcoding. Herein, we directly compare the usefulness of COI and 16S in discriminating species of hynobiid salamanders using 130 individuals. Species identification and classification of these animals, which are endemic to Asia, are often based on morphology only. Analysis of Kimura 2-parameter genetic distances (K2P) documents the mean intraspecific variation for COI and 16S rRNA genes to be 1.4% and 0.3%, respectively. Whereas COI can always identify species, sometimes 16S cannot. Intra- and interspecific genetic divergences occasionally overlap in both markers, thus reducing the value of a barcoding gap to identify genera. Regardless, COI is the better DNA barcoding marker for hynobiids. In addition to the comparison of two potential markers, high levels of intraspecific divergence in COI (>5%) suggest that both Onychodactylus fischeri and Salamandrella keyserlingii might be composites of cryptic species.     

Random Amplified Polymorphic DNA Analysis of Heterodera cruciferae and H. schachtii populations

Heterodera schachtii and H. cruciferae are sympatric in California and frequently occur in the same field upon the same host. We have investigated the use of polymerase chain reaction (PCR) amplification of nematode DNA sequences to differentiate H. schachtii and H. cruciferae and to assess genetic variability within each species. Single, random oligodeoxyribonucleotide primers were used to generate PCR-amplified fragments, termed RAPD (random amplified polymorphic DNA) markers, from genomic DNA of each species. Each of 19 different random primers yielded from 2 to 12 fragments whose size ranged from 200 to 1,500 bp. Reproducible differences in fragment patterns allowed differentiation of the two species with each primer. Similarities and differences among six different geographic populations of H. schachtii were detected. The potential application of RAPD analysis to relationships among nematode populations was assessed through cluster analysis of these six different populations, with 78 scorable markers from 10 different random primers. DNA from single cysts was successfully amplified, and genetic variability was revealed within geographic populations. The use of RAPD markers to assess genetic variability is a simple, reproducible technique that does not require radioisotopes. This powerful new technique can be used as a diagnostic tool and should have broad application in nematology.     

Estimation of genetic diversity and evaluation of relatedness through molecular markers among medicinally important trees: <Emphasis Type="Italic">Terminalia arjuna</Emphasis>, <Emphasis Type="Italic">T. chebula</Emphasis> and <Emphasis Type="Italic">T. bellerica</Emphasis>

Terminalia trees are being over-exploited because of their medicinal and economical importance leading to loss of valuable genetic resources. For sustainable utilization and conservation, assessment of genetic diversity therefore becomes imperative. We report a comprehensive first study on estimation and analysis of genetic variation through Amplified fragment length polymorphism (AFLP), inter simple sequence repeat polymorphism (ISSR) and random amplification of polymorphic DNA (RAPD) across three species of Terminalia. The study included (i) characterization of genetic diversity at interspecific level, and (ii) comparison of efficiency of the marker systems. That the three species are genetically distinct was revealed by all the three marker systems as unique DNA fingerprints were obtained. This led to identification of several species-specific amplification products. Further analysis helped in species-wise clustering. The species specific bands obtained from the present investigation can be used as diagnostic markers to identify the raw materials for herbal drug preparations for authentication purposes.     

林麝和马麝随机扩增多态DNA的研究

用随机扩增多态 DNA(RAPD)技术对饲养的林麝和马麝进行分子遗传标记研究。在选用的42 种随机引物中, 有25种引物产生了清晰稳定的条带, 单个引物获得标记数在1～14 之间,平均每个个体获得168个RAPD标记 , 其中林麝、马麝特异性标记各5个,个体特异性标记有3个, 这些标记可用来鉴定种或个体。平均遗传距离在林麝种内为0.27±0.023, 马麝为0.105±0.013, 种间为0.241±0.02 , 种间差异显著大于种内差异。分析表明饲养马麝种内遗传多样性低, 为增强饲养马麝的生存力, 最好从不同种群中引入种麝进行繁殖。     

Comparison of RFLP and RAPD markers to estimating genetic relationships within and among cruciferous species

Restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) markers are being used widely for evaluating genetic relationships of crop germplasm. Differences in the properties of these two markers could result in different estimates of genetic relationships among some accessions. Nuclear RFLP markers detected by genomic DNA and cDNA clones and RAPD markers were compared for evaluating genetic relationships among 18 accessions from six cultivated Brassica species and one accession from Raphanus sativus. Based on comparisons of genetic-similarity matrices and cophenetic values, RAPD markers were very similar to RFLP markers for estimating intraspecific genetic relationships; however, the two marker types gave different results for interspecific genetic relationships. The presence of amplified mitochondrial and chloroplast DNA fragments in the RAPD data set did not appear to account for differences in RAPD- and RFLP-based dendrograms. However, hybridization tests of RAPD fragments with similar molecular weights demonstrated that some fragments, scored as identical, were not homologous. In all these cases, the differences occurred at the interspecific level. Our results suggest that RAPD data may be less reliable than RFLP data when estimating genetic relationships of accessions from more than one species.     

A sex-associated sequence identified by RAPD screening in gynogenetic individuals of turbot (Scophthalmus maximus)

Understanding the genetic basis of sex determination mechanisms is essential for improving the productivity of farmed aquaculture fish species like turbot (Scophthalmus maximus). In culture conditions turbot males grow slower than females starting from eight months post-hatch, and this differential growth rate is maintained until sexual maturation is reached, being mature females almost twice as big as males of the same age. The goal of this study was to identify sex-specific DNA markers in turbot using comparative random amplified polymorphism DNA (RAPD) profiles in males and females to get new insights of the genetic architecture related to sex determination. In order to do this, we analyzed 540 commercial 10-mer RAPD primers in male and female pools of a gynogenetic family because of its higher inbreeding, which facilitates the detection of associations across the genome. Two sex-linked RAPD markers were identified in the female pool and one in the male pool. After the analysis of the three markers on individual samples of each pool and also in unrelated individuals, only one RAPD showed significant association with females. This marker was isolated, cloned and sequenced, containing two sequences, a microsatellite (SEX01) and a minisatellite (SEX02), which were mapped in the turbot reference map. From this map position, through a comparative mapping approach, we identified Foxl2, a relevant gene related to initial steps of sex differentiation, and Wnt4, a gene related with ovarian development, close to the microsatellite and minisatellite markers, respectively. The position of Foxl2 and Wnt4 was confirmed by linkage mapping in the reference turbot map.     

Molecular identification of five Indian sciaenids (pisces: perciformes,sciaenidae) using RAPD markers

The randomly amplified polymorphic DNA (RAPD) markers were used to detect interspecific genetic variability and genetic relatedness among five Indian sciaenids namely Otolithes cuvieri, Johnieops sina, Johnieops macrorhynus, Johnieops vogleri and Protonibea diacanthus for the first time. Eight RAPD primers (OPA01, OPA06, OPA07, OPA18, OPP12, OPP14, OPP16 and OPP11) generated 40 species specific diagnostic bands. The highest genetic divergence was detected between J. macrorhynus and P. diacanthus (0.586) where as the lowest one was observed between J. sina and J. vogleri (0.274). Handling editor: C. Strumbauer     

Morphological and genetic differentiation among four pigment producing Indian species of <Emphasis Type="Italic">Phoma</Emphasis> (Saccardo, 1899)

A PCR-based technique, involving the random amplification of polymorphic DNA (RAPD), was used for assessing genetic relatedness among isolates of the genus Phoma. Randomly Amplified Polymorphic DNA (RAPD) revealed the presence of interspecific genetic variation among the pigment producing isolates of Phoma and has shown distinct phylogenetic cluster. The major objective of the study was to study the genetic variation, if any. Study was aimed to differentiate four pigment producing species of Phoma based on morphological studies and molecular markers in general and RAPD in particular. We found that the test species of Phoma can be very well differentiated using molecular markers. Phoma sorghina was differentiated from P. exigua, P. fimeti and P. herbarum. RAPD profiles of P. herbarum and P. fimeti has shown the maximum similarity, which indicates the genetic relatedness among these two species which were considered earlier as distinct species based on morphological observation.     

Sexing birds using random amplified polymorphic DNA (RAPD) markers

We used random amplified polymorphic DNA (RAPD) markers to sex birds from small tissue (usually blood) samples. Arbitrarily chosen 10-mer PCR primers were screened with DNA from known-sex individuals for the production of a bright female-specific band. Suitable primers were found for seven bird species after screening about 30 primers (range 2–63), and no primer was found for three other species after screening about 50 primers for each species. Investigations into the reliability of RAPD markers for sexing great tits Parus major and oystercatchers Haematopus ostralegus show that: (i) when PCR reaction conditions for great tit DNA are varied, either the presence of the female-specific band correctly predicts the individual's sex or no DNA amplification occurs; (ii) the female-specific band in great tits can be sequenced, and subsequently amplified using specific PCR primers; (iii) null alleles of the female-specific fragment occur at an estimated frequency of 0% ( n = 241 females) in great tits and 0.6% ( n > 290 females) in oystercatchers; (iv) the female-specific fragment in great tits occurs in individuals from a wide geographical range encompassing two subspecies; and (v) the relative intensity of bands in great tit RAPD banding profiles is consistent across individual birds and scorers. The RAPD primers that we have identified are generally species specific, and the consequent time cost of screening for primers is the chief disadvantage of using RAPD markers to sex birds. However, with large sample sizes this disadvantage is outweighed by the relative technical simplicity and low cost of the technique.     

Assessment of genetic variability through ISSR and RAPD markers in <Emphasis Type="Italic">Commiphora wightii</Emphasis> (Arn.) Bhandari

Commiphora wightii (Arn.) Bhandari is a commercially, medicinally and traditionally important tropical shrub widely used to treat various ailments and disorders. Demand of this plant is increasing in the pharmaceutical and perfumery industries due to the presence of guggulsterone E and Z, two important isomers conferring lipid- and cholesterol-lowering, and anti-cancerous properties. Ruthless and unscientific harvesting of oleo-gum resin by local populations from the wild, with negligible conservation efforts has made this species endangered and led to its inclusion in the Red Data Book of IUCN. It is imperative to have broad information regarding the extent of genetic variability available in the species to accelerate the breeding and conservation programs. Therefore, the present study was undertaken to analyze the extent of genetic variability existing among the C. wightii germplasm collected from Rajasthan and Haryana, the diversity rich Indian states, using ISSR and RAPD markers. A total of 100 (50 each) RAPD and ISSR markers were screened of which 37 RAPD and 43 ISSR primers were able to amplify DNA fragments. RAPD markers were more efficient, detecting 74.16 % polymorphism, compared to ISSR which detected 62.52 % polymorphism. Also, the values of average number of polymorphic bands per assay, polymorphism information content (PIC), diversity index (DI) and marker index (MI) were more for RAPD (7.76, 0.19, 0.38 and 2.53, respectively) than for ISSR (7.02, 0.13, 0.32 and 1.88) markers. The UPGMA dendrogram constructed using individual as well as combined data of the two marker systems separated the collected accessions into two major clusters containing 47 and 4 accessions, respectively, while one accession from Bikaner was not included in any cluster. Genetic similarity values obtained from Jaccard’s coefficient using combined data of both the marker systems were between 0.50 and 0.97. These results indicated the existence of wide genetic variability within this species and can be used for further research in the area of germplasm conservation, population genetics and plant breeding.     

Fast discrimination (RAPD-PCR) of the species forming the pest complex Aleurodicus dispersus–Lecanoideus floccissimus (Hom: Aleyrodidae)

Abstract:  The Aleurodicus dispersus–Lecanoideus floccissimus complex has become a very important agricultural pest in the Canaries. These species are not easily differentiated by their morphological characteristics. The aim of the present study was to obtain genetic markers to unambiguously distinguish both species of this complex. Thus, six random primers were employed to generate RAPD markers. Different RAPD profiles were observed for the different species. The analysis successfully identified 39 reproducible and specific markers for L. floccissimus and 51 for A. dispersus , i.e. bands present in all individuals of one species but never in the other. RAPD markers resulted a useful tool for discriminate both species. Early identification of species and also of biotypes is crucial when designing control strategies to avoid the spread of the pest and consequently the considerable economic losses it causes in tropical crops.     

High genetic differentiation among remnant populations of the endangered Caesalpinia echinata Lam. (Leguminosae–Caesalpinioideae)

Forest fragments along the Atlantic coastland of Brazil have been highly impacted by extensive human activities for the last 400 years. Caesalpinia echinata (Leguminosae– Caesalpinioideae), brazilwood, was overexploited during this period due to its economical importance as a dye. As a result, the species has become endangered and today its total population size is very restricted. We have assessed the distribution of genetic variation between five natural populations of brazilwood by means of RAPD (random amplified polymorphic DNA) markers. Of the total genetic variability, 28.5% was attributable to differences between two geographical groups, 29.6% to population differences within groups and 42.0% to individual differences within populations. The high level of population differentiation observed is in contrast to that expected for a primarily outcrossed woody perennial plant, and suggests that there may be a degree of inbreeding. Our results are in agreement with previous studies which postulated that C. echinata has always occurred in clumps, being common in some places but rare in between. From a conservation point of view, different populations representing different regions should be protected and, yet, plants with different origins should not be synthesized into populations in a recovery process at the risk of loss and dilution of genetic information. This study demonstrates that RAPD markers were effective in establishing a clear correlation between genetic and geographical distance and in identifying areas of maximum diversity, and may be used as an initial approach to assess the partitioning of genetic variation in this endangered species.     

DNA fragments of organellar origin in random amplified polymorphic DNA (RAPD) patterns of sugar beet (Beta vulgaris L.)

The technique of random amplified polymorphic DNA (RAPD) offers a broad range of applications in the investigation of plant genomes. A promising prospect is the use of RAPD products as genetic markers. We have investigated a possible organellar source of fragments in RAPD patterns of total DNA. Two nearly-isogenic lines of cytoplasmic male-sterile and male-fertile sugar beet (Beta vulgaris L.) were subjected to RAPD analysis with six different primers. Total, nuclear, mitochondrial (mt), and chloroplast (cp), DNA from each line were investigated. Reproducible DNA fingerprints could be obtained from both organellar DNAs. Differences in band patterns of mtDNA between cytoplasmic male-sterile and -fertile lines were observed with five out of six primers, whereas different cpDNA patterns were generated by one of the primers. Consequently, the RAPD technique can be used to discriminate between different cytoplasms. Clear evidence is provided for the organellar origin of fragments in genomic (total DNA) RAPD patterns. The consequences of these results for the interpretation of RAPD analyses are discussed.     

Molecular differentiation of the Old World Culicoides imicola species complex (Diptera, Ceratopogonidae), inferred using random amplified polymorphic DNA markers

Samples of seven of the 10 morphological species of midges of the Culicoides imicola complex were considered. The importance of this species complex is connected to its vectorial capacity for African horse sickness virus (AHSV) and bluetongue virus (BTV). Consequently, the risk of transmission may vary dramatically, depending upon the particular cryptic species present in a given area. The species complex is confined to the Old World and our samples were collected in Southern Africa, Madagascar and the Ivory Coast. Genomic DNA of 350 randomly sampled individual midges from 19 populations was amplified using four 20-mer primers by the random amplified polymorphic DNA (RAPD) technique. One hundred and ninety-six interpretable polymorphic bands were obtained. Species-specific RAPD profiles were defined and for five species diagnostic RAPD fragments were identified. A high degree of polymorphism was detected in the species complex, most of which was observed within populations (from 64 to 76%). Principal coordinate analysis (PCO) and cluster analysis provided an estimate of the degree of variation between and within populations and species. There was substantial concordance between the taxonomies derived from morphological and molecular data. The amount and the different distributions of genetic (RAPD) variation among the taxa can be associated to their life histories, i.e. the abundance and distribution of the larval breeding sites and their seasonality.     

Identification of SCAR marker linking to longer frond length of <Emphasis Type="Italic">Saccharina japonica</Emphasis> (Laminariales,Phaeophyta) using bulked-segregant analysis

To construct a molecular-marker-assisted selection (MAS) system, research was done on identifying molecular markers linking to longer frond length, a crucial selection index in the breeding of the commercially important seaweed Saccharina japonica. An F₂-segregant population of 92 individuals was obtained by crossing two prominent S. japonica strains. Genomic DNA from ten individuals with the longest frond and ten individuals with the shortest frond in the F₂-segregant population were mixed to create two DNA pools for screening polymorphic markers. In bulked-segregant analysis (BSA), out of 100 random amplified polymorphic DNA (RAPD) primers only two produced three polymorphic RAPD markers between the two DNA pools. In conversion of the three RAPD markers into sequence-characterized amplified region (SCAR) markers, only one was successfully converted into a SCAR marker FL-569 linking to the trait of longer frond. Test of the marker FL-569 showed that 80% of the individuals with longest fronds in a wild population and 87.5% of individuals with the longest fronds in an inbred line “Zhongke No. 2” could be detected by FL-569. Additionally, genetic linkage analysis showed that the SCAR marker could be integrated into the reported genetic map and QTL mapping showed that FL-569 linking to qL1-1. The obtained marker FL-569 will be beneficial to MAS in S. japonica breeding.     

Random amplified polymorphic DNA markers for discriminating Cochliomyia hominivorax from C. macellaria (Diptera: Calliphoridae)

The screwworm, Cochliomyia hominivorax (Coquerel), is one of the most important pests of livestock in the Western Hemisphere. During early immature stages it is morphologically very similar (first instars are virtually indistinguishable) to the secondary screwworm, C. macellaria (Fabricius). Here, the utility of the random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) was explored as a technique for developing molecular genetic markers for these two species. Of the 120 arbitrary primers screened, 21 primers produced markers that were further investigated. Seven of the 21 primers produced clear and reproducible markers that were tested with DNA of five individuals from four populations of each species; five of these primers showed 12 RAPD markers that differentiated the species in all populations. Analyses of data from these seven primers also suggested that intraspecific polymorphisms exist that could be useful in distinguishing populations of screwworms. Some population genetic tools, such as genetic distance, cluster analysis and bootstrapping, were used to statistically explore these polymorphisms. The resulting statistics showed 100% support for the ability of RAPD-PCR to discriminate between the two species. Bootstrapping with data from one of the genetic distance calculations produced a tree with all individual screwworms in the correct populations, indicating that RAPD-PCR has promise for displaying intraspecific genetic variation that could be used in establishing the general geographic origin of screwworm samples.