Assessing Nuclear and Mitochondrial DNA Sequence Variation Within Steinernema (Rhabditida: Steinernematidae)

DNA sequence analysis was used to characterize the nuclear ribosomal DNA ITS1 region and a portion of the COII and 16S rDNA genes of the mitochondrial genome from Steinernema entomopathogenic nematodes. Nuclear ITS1 nucleotide divergence among seven Steinernema spp. ranged from 6 to 22%, and mtDNA divergence among five species ranged from 12 to 20%. No intraspecific variation was observed among three S. feltiae strains. Phylogenetic analysis of both nuclear and mitochondrial DNA sequences confirms the existing morphological relationships of several Steinernema species. Both the rDNA ITS1 and mtDNA sequences were useful for resolving relationships among Steinernema taxa.     

Genetic differentiation of charrs in the Russian north and far east

Genetic differences and relationships within charrs Salvelinus alpinus , northern and southern S. malma, S. taranetzi, S. levanidovi and S. leucomaenis , were studied by examination of 31–35 allozyme loci and PCR-RFLP analysis of mtDNA segment (about 2600 bp) including the cytochrome b gene and D-loop. Data for mtDNA were also obtained for samples of S. drjagini, S. albus and for European samples of S. alpinus. Generally allozyme and mtDNA segment analyses produced similar pictures of genetic divergence and relationships. The southern S. malma exhibited the greatest genetic variability (allozyme heterozygosity and mtDNA haplotype diversity). S. alpinus, S. malma, S. levanidovi and S. leucomaenis had fixed differences from one another at various allozyme loci, and differed in fixed (but polymorphic in S. malma ) individual mtDNA haplotypes produced with MspI restrictase. Such genetic individuality is typical of distinct taxa. S. taranetzi is closest genetically to allopatric S. alpinus , but exhibited fixed differences from the northern S. malma in sympatry. In all samples of S. alpinus the only mtDNA haplotype was shared with S. drjagini. S. albus shared its single haplotype with the northern S. malma from the same locality. S. leucomaenis is differentiated from the other species to the greatest extent, possibly reflecting an early evolutionary divergence. Some evolutionary and taxonomic implications of the genetic relationships of charrs studied are discussed.     

Molecular systematics of the endemic Leptaxini (Gastropoda: Pulmonata) on the Azores islands

The Azorean representatives of the Leptaxini (Pulmonata) are single island endemics, where a high-spired shell distinguishes the monotypic genus Helixena from two slightly different low-spired forms within Leptaxis (azorica and caldeirarum type). We studied the evolutionary history of putative taxa and the three shell-types using 12 allozyme loci and sequences of nuclear (ITS-1 and ITS-2) and mitochondrial DNA (COI and 16S rRNA). While little variation was found in both ITS genes, allozyme and mtDNA divergence was among the highest reported for pulmonate land snails. Generally, phylogeographic patterns are indicative of allopatric differentiation via the successive colonization of (younger) islands, while a major role for adaptive evolution is not supported. The azorica shell-type is monophyletic and has no common history with other sympatric shell-types on the same islands. The (ambiguous) position of Helixena sanctaemariae makes Leptaxis paraphyletic on the Azores and possibly also the caldeirarum shell-type. Helixena can therefore not be distinguished as a separate genus on the Azores. Following a lineage-based concept, representatives on all (ancient) islands should be considered distinct species.     

GEOGRAPHIC DISTRIBUTION OF MOLECULAR VARIANCE WITHIN THE BLUE MARLIN (MAKAIRA NIGRICANS): A HIERARCHICAL ANALYSIS OF ALLOZYME,SINGLE-COPY NUCLEAR DNA,AND MITOCHONDRIAL DNA MARKERS

This study presents a comparative hierarchical analysis of variance applied to three classes of molecular markers within the blue marlin (Makaira nigricans). Results are reported from analyses of four polymorphic allozyme loci, four polymorphic anonymously chosen single-copy nuclear DNA (scnDNA) loci, and previously reported restriction fragment length polymorphisms (RFLPs) of mitochondrial DNA (mtDNA). Samples were collected within and among the Atlantic and Pacific Oceans over a period of several years. Although moderate levels of genetic variation were detected at both polymorphic allozyme (H = 0.30) and scnDNA loci (H = 0.37), mtDNA markers were much more diverse (h = 0.85). Allele frequencies were significantly different between Atlantic and Pacific Ocean samples at three of four allozyme loci and three of four scnDNA loci. Estimates of allozyme genetic differentiation (θ_O) ranged from 0.00 to 0.15, with a mean of 0.08. The θ_O values for scnDNA loci were similar to those of allozymes, ranging from 0.00 to 0.12 with a mean of 0.09. MtDNA RFLP divergence between oceans (θ_O = 0.39) was significantly greater than divergence detected at nuclear loci (95% nuclear confidence interval = 0.04–0.11). The fourfold smaller effective population size of mtDNA and male-mediated gene flow may account for the difference observed between nuclear and mitochondrial divergence estimates.     

Phylogeny and a new species of Sparassis (Polyporales, Basidiomycota): evidence from mitochondrial atp6, nuclear rDNA and rpb2 genes

Three nuclear genes, lsu-rDNA (encoding nuclear large subunit rDNA), ITS (encoding the rDNA internal transcribed spacers and 5.8 S rDNA) and rpb2 (encoding the second largest subunit of RNA polymerase II), and the mitochondrial gene atp6 (encoding the sixth subunit of ATP synthase), were sequenced from all recognized Sparassis lineages. Sparassis latifolia sp. nov. from boreal coniferous forests in China is described based on morphological, ecological, geographical and molecular data. The nuclear gene phylogeny strongly supported groups corresponding to morphological differences, geographic distribution and host shifts among species that produce clamp connections, such as S. crispa from Europe, S. radicata from western North America and S. latifolia from Asia. The atp6 phylogeny however showed no divergence among these three species. For clampless Sparassis species, such as S. spathulata from eastern North America, S. brevipes and a new species from Europe, the atp6 phylogeny was congruent with the nuclear gene phylogeny. Sparassis cystidiosa is basal in the nuclear tree but sister to S. brevipes-S. spathulata clade in the ATP6 tree. The differences between the phylogenetic inferences from the atp6 gene and those from nuclear genes within Sparassis species are discussed.     

Genetic population structure of red snappers (Lutjanus malabaricus Bloch & Schneider, 1801 and Lutjanus erythropterus Bloch, 1790) in central and eastern Indonesia and northern Australia

The genetic population structure of red snapper Lutjanus malabaricus and Lutjanus erythropterus in eastern Indonesia and northern Australia was investigated by allozyme electrophoresis and sequence variation in the control region of mtDNA. Samples were collected from eight sites in Indonesia and four sites in northern Australia for both species. A total of 13 allozyme loci were scored. More variable loci were observed in L. malabaricus than in L. erythropterus . Sequence variation in the control region (left domain) of the mitochondrial genome was assessed by RFLP and direct sequencing. MtDNA haplotype diversity was high ( L. erythropterus , 0·95 and L. malabaricus , 0·97), as was intraspecific sequence divergence, ( L. erythropterus , 0·0–12·5% and L. malabaricus , 0·0–9·5%). The pattern of mtDNA haplotype frequencies grouped both species into two broad fisheries stocks with a genetic boundary either between Kupang and Sape ( L. malabaricus ) or between Kupang and Australian Timor Sea ( L. erythropertus ). The allozyme analyses revealed similar boundaries for L. erythropterus . Seven allozymes stocks compared to two mtDNA stocks of L. malabaricus including Ambon, which was not sampled with mtDNA, however, were reported. Possible reasons for differences in discrimination between the methods include: i) increased power of multiple allozyme loci over the single mtDNA locus, ii) insufficient gene sampling in the mtDNA control region and iii) relative evolutionary dynamics of nuclear (allozyme loci) and mitochondrial DNA in these taxa. Allozyme and haplotype data did not distinguish separate stocks among the four Australian locations nor the central Indonesian (Bali and Sape locations) for both L. malabaricus and L. erythropterus.     

Molecular phylogeny of North American Branchiobdellida (Annelida: Clitellata)

Branchiobdellidans, or crayfish worms, are ectosymbiotic clitellate annelids associated primarily with freshwater crayfishes. The main objectives of our study were to infer a molecular phylogeny for the North American Branchiobdellida, examine its congruence with morphology-based hypotheses of relationships at the subfamily and genus level, and use our dataset to assess consistency of GenBank-archived branchiobdellidan sequences. We used nucleotide sequence data from two mtDNA genes (COI and 16S rDNA) and three nuclear genes (28S rDNA, 18S rDNA, and ITS1) to estimate phylogenetic relationships among 47 described and one undescribed species of Branchiobdellida. We recovered a monophyletic branchiobdellidan clade with generally short branch lengths, suggesting that a large portion of the taxon has likely undergone a recent and rapid radiation in North America. Results from our phylogenetic analyses indicate that current taxonomic groupings are largely unsupported by the molecular data. All four subfamilies are either paraphyletic or polyphyletic, and only three of seven sampled non-monotypic genera were monophyletic. We found a high rate (49%) of inconsistency in GenBank-archived sequences, over 70% of which can be attributed to field- or laboratory-based error.     

Molecular and morphological data reveal cryptic taxonomic diversity in the terrestrial slug complex Arion subfuscus/fuscus (Mollusca, Pulmonata, Arionidae) in continental north-west Europe

The importance and abundance of cryptic species among invertebrate taxa is well documented. Nowadays, taxonomic, phylogenetic and conservation biological studies frequently use molecular markers to delineate cryptic taxa. Such studies, however, often face the problem of the differential resolution of the molecular markers and techniques involved. This issue is explored in the present study of cryptic taxa within the terrestrial slug complex Arion subfuscus/fuscus in continental north-west Europe. To this end, morphological, allozyme and mitochondrial 16S rDNA sequence data have been jointly evaluated. Using allozyme data and gonad type, two distinct groups were consistently delineated, even under sympatric conditions. The 16S rDNA data strongly supported both those groups and even suggested the presence of three distinct taxa within one of them. However, in view of: (1) the allopatric distribution of three OTUs, (2) the lack of allozyme or morphological differentiation, and (3) the extremely high degree of intraspecific mtDNA variation reported in pulmonate gastropods, they are, for the time being, not regarded as valid species under the biological species concept. By means of 16S rDNA and allozyme data, the position of type and topotype material of A. subfuscus s.s. and A. fuscus relative to the newly defined OTUs was determined, thus clarifying the nomenclature of this species complex. Additionally, gonad type proved to be a useful character for distinguishing the two species in north-west Europe.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 23–38.     

A maximum-likelihood analysis of eight phylogenetic markers in gallwasps (Hymenoptera: Cynipidae): implications for insect phylogenetic studies

We assessed the utility of eight DNA sequence markers (5.8S rDNA, 18S rDNA, 28S rDNA, ITS regions, long-wavelength opsin, elongation factor 1-alpha, cytochrome b, and cytochrome oxidase I) in reconstructing phylogenetic relationships at various levels of divergence in gallwasps (Hymenoptera: Cynipidae), using a set of eight exemplar taxa. We report sequence divergence values and saturation levels and compare phylogenetic results of these sequences analyzed both separately and combined to a well-corroborated morphological phylogeny. Likelihood ratio tests were used to find the best evolutionary model fitting each of the markers. The likelihood model best explaining the data is, for most loci, parameter rich, with strong A-T bias for mitochondrial loci and strong rate heterogeneity for the majority of loci. Our data suggest that 28S rDNA, elongation factor 1-alpha, and long-wavelength opsin may be potentially useful markers for the resolution of cynipid and other insect within-family-level divergences (circa 50-100 mya old), whereas mitochondrial loci and ITS regions are most useful for lower-level phylogenetics. In contrast, the 18S rDNA marker is likely to be useful for the resolution of above-family-level relationships.     

Geographic ranges, population structure, and ages of sexual and parthenogenetic snail lineages

Abstract A sexual reproduction is thought to doom organisms to extinction due to mutation accumulation and parasite exploitation. Theoretical models suggest that parthenogens may escape the negative effects of conspecific and biological enemiecs through escape in space. Through intensive sequencing of a mitochondrial DNA (mtDNA) and a nuclear intron locus in sexual and pathenogenetic freshwater snails (Campelom), I examine three questionss: (1) Are sexual mtDNA lineage more restricted geographically than parthenogenetic mtDNA lineages? (2) Are independent pathenogenetic lineages shorter lived than sexual lineages? (3) Do pathenogens have higher intraindividual nuclear sequence diversity and form well‐differentiated monophyletic groups as expected under the Meselson effect? Geographic ranges of parthenogenetic lineages are significantly larger than geographic ranges of sexual lineages. Based on coalescence times under different deographic assumptions, asexual lineages are short lived, but there is variation in clonal ages. Although alternative explanations exit, these results suggest that asexual lineages may persist in the short term through dispersal, and that various constraints may cause geographic restriction of sexual lineagess. Both allotriploid and diploid Campleloma parthenogens have significantly higher allelic divergence within individuals, but show limited nuclear sequence divergence from sexual ancestors. In contrast to previous allozyme evidence for nonhybrid origins of diploid Campeloma parthenogens, cryptic hybridization may account for elevated heterozygosity.     

Mitochondrial DNA variation in the hybridizing fire-bellied toads, Bombina bombina and B. variegata

Using five restriction enzymes, geographical variation of mitochondrial DNA (mtDNA) in Bombina bombina and B. variegata was studied in samples from 20 locations. Each restriction enzyme produced a species-specific fragment pattern. B. bombina haplotypes A and B were closely related to each other. In contrast, haplotypes A and B of B. variegata formed two distinct lineages. A very distinctive haplotype (C) was found in the Carpathian Mountains, whereas two other haplotypes, D and E (differing by a single AvaI site), were present in western Europe and the Balkans, respectively. Populations polymorphic for haplotypes D and E occurred in the central Balkans where the haplotypes could replace each other clinally. mtDNA sequence divergence between B. bombina and B. variegata was estimated as 6.0-8.1% and 4.7-5.2% between type C and types D/E of B. variegata. The latter divergence is contrary to allozyme and morphological data that place the western and Carpathian B. v. variegata together (Nei's D = 0.07) and separate them from the Balkan subspecies B. v. scabra (Nei's D = 0.18). Broad interspecific correlation among morphology, allozymes and mtDNA types in European fire-bellied toads argues that, despite continuous hybridization (interrupted perhaps during Pleistocene glacial maxima), little or no mtDNA introgression between the species has occurred outside the narrow hybrid zones that separate these parapatric species.     

Incongruous nuclear and mitochondrial phylogeographic patterns in two sympatric lineages of the wolf spider Pardosa astrigera (Araneae: Lycosidae) from China

We investigated the genetic structure of mitochondrial DNA (COI and 16S rRNA-tRNA(Leu(CUN))-ND1) and nuclear DNA (ITS2) variations among and within populations of Pardosa astrigera in China. Two phenotypes of males were recognized. They differed genetically also in the presence (type A) or absence (type B) of common insertions and deletions in ITS2. The concordance between mtDNA based phylogeny and the phenotypic variations of P. astrigera was weak. Haplotypes of type A did not form a monophyletic group. Instead they were found in three clades, in one of them mixed with type B haplotypes, most likely as a result of long-term and ongoing gene flow of mtDNA between the two phenotypic groups (M = 0.69). Pairwise sequence divergences of all data sets indicated that the genetic divergences between the two phenotypes fall within intraspecific range. Our results indicated that the P. astrigera populations in China consist of two sympatric lineages with male phenotypic variations. Patterns of mismatch distribution within lineages suggested long-term demographic stability in the lineage A, and growth in lineage B that expanded rapidly and recolonized from a southern refuge to the northern parts of China during the late-Pleistocene. On the basis of the estimated divergence time between the two lineages (0.18-0.41 Ma), we suggest that the dry-cold climate and the uplift of the Tibetan plateau during the mid-Pleistocene appear to have a determinating impact on the evolutionary history of P. astrigera in China.     

GENETIC EVIDENCE FOR REPRODUCTIVE ISOLATION AND MULTIPLE ORIGINS OF SYMPATRIC TROPHIC ECOTYPES OF WHITEFISH (COREGONUS)

We assessed variation in mitochondrial DNA (mtDNA) by restriction fragment length polymorphism (RFLP) analysis and in nuclear genes by allozyme analysis among sympatric pairs of limnetic and benthic ecotypes of whitefish (Coregonus) coexisting in three lakes of southern Yukon to address three evolutionary questions regarding their origins. Are sympatric low and high gill-raker count ecotypes genetically differentiated? Are they issued from monophyletic or polyphyletic evolutionary events? If they are polyphyletic in origins, did they originate from multiple allopatric speciation events or intralacustrine radiation? Our results corroborated previous genetic and ecological studies of these ecotypes, indicating that they represent genetically distinct reproductive units, and therefore refuting the hypothesis of phenotypic polymorphism within a single population. However, the amount of gene flow between ecotypes varied among lakes, correlating with the extent of morphological differentiation and the potential for premating reproductive isolation. The results indicated a polyphyletic origin of ecotypes whereby each of them have been expressed independently more than once. In the two lakes of Squanga Creek drainage, the existence of sympatric pairs was best explained by the secondary contact of two monophyletic whitefish groups that evolved in allopatry during the last glaciation events. In Dezadeash L. of Alsek R. drainage, our results could not verify either sympatric or allopatric (or microallopatric) origin of ecotypes. Regardless of the mode of speciation involved in their origins, these sympatric whitefish populations provided further evidence that Pleistocene glaciation events created conditions favoring rapid divergence and phenotypic differentiation among northern freshwater fishes.     

Non-concerted ITS evolution, early origin and phylogenetic utility of ITS pseudogenes in Pyrus

Molecular studies of 19 species of the genus Pyrus L. revealed different degrees of intra-individual polymorphism of the internal transcribed spacer (ITS 1, 5.8S rDNA and ITS 2) region due to the existence of putative non-functional copies (pseudogenes), putative recombinants and non-concerted evolution among functional copies. Different types of ITS pseudogenes displaying lower GC content and unstable secondary structure were preferentially amplified under normal PCR conditions. Functional ITS copies were successfully obtained in all investigated accessions under the modified PCR conditions. All pseudogenes were highly divergent from their corresponding functional copies and formed a monophyletic group in the phylogenetic tree based on all paralogs, indicating they were of relatively early origin. Functional ITS copies led to confused and poorly resolved phylogeny as a result of low sequence divergence, existence of unidentified ancient recombinants and a high degree of intra-individual functional ITS polymorphism, while certain types of pseudogenes and some relict pseudogenes offered more credible clues for the evolutionary history of Pyrus species.     

Nuclear ribosomal DNA monophyly versus mitochondrial DNA polyphyly in two closely related mite species: the influence of life history and molecular drive

In two very closely related but reproductively isolated mite species, Tetranychus urticae and T. turkestani, we found nucleotide diversity to be extensive for mitochondrial DNA (mtDNA) cytochrome oxidase 1 (COI) (3-4%) but extremely reduced for nuclear ribosomal DNA (rDNA) internal transcribed spacer (ITS2) (less than 0.5%). By contrast, ITS2 was shown to evolve much faster than COI between species of this genus. Furthermore, we found that these two species are polyphyletic for mtDNA but monophyletic for rDNA. Thus it appears that despite its biparental transmission and multiplicity of copies in the genome, nuclear rDNA has a smaller effective population size than mtDNA in these species. The conjunction of efficient concerted evolution and/or gene conversion in the rDNA cluster, the haplodiploidy of these species and their female-biased sex ratio could account for this apparent contradiction.     

PHYLOGENETIC RELATIONSHIPS AND MOLECULAR VARIABILITY WITHIN AND AMONG SIX CHROMOSOME RACES OF SCELOPORUS GRAMMICUS (SAURIA,IGUANIDAE), BASED ON NUCLEAR AND MITOCHONDRIAL MARKERS

Selected populations of Sceloporus grammicus from central Mexico were karyotyped and screened for variability at the protein, ribosomal-DNA, and mitochondrial-DNA levels. Molecular markers were used to construct phylogenies of the chromosome races, which were then qualitatively evaluated for congruence with each other and with the original chromosomal phytogeny proposed by Hall (1973). Between-cytotype protein divergence generally was low, and few allozyme markers were fixed between cytotypes. Hence, these data were combined with the rDNA restriction-site data for phylogeny reconstruction. This combined nuclear data set provided a phylogenetic hypothesis that, with one exception, is reasonably congruent with that based on standard karyotypes. Similar results were obtained from mtDNA restriction-site data, although there are some discrepancies, and trees based on both DNA data sets are complicated by evidence for historical and/or ongoing hybridization. An unexpectedly rapid rate of rDNA divergence is demonstrated relative to the degree of allozyme divergence, suggesting that restriction-site variation in rDNA has systematic utility at lower taxonomic levels.     

New taxa refresh the phylogeny and classification of pleurostomatid ciliates (Ciliophora,Litostomatea)

A high diversity of pleurostomatid ciliates has been discovered in the last decade, and their systematics needs to be improved in the light of new findings concerning their morphology and molecular phylogeny. In this work, a new genus, Protolitonotus gen. n., and two new species, Protolitonotus magnus sp. n. and Protolitonotus longus sp. n., were studied. Furthermore, 19 novel nucleotide sequences of SSU rDNA, LSU rDNA and ITS1‐5.8S‐ITS2 were collected to determine the phylogenetic relationships and systematic positions of the pleurostomatid ciliates in this study. Based on both molecular and morphological data, the results demonstrated that: (i) as disclosed by the sequence analysis of SSU rDNA, LSU rDNA and ITS1‐5.8S‐ITS2, Protolitonotus gen. n. is sister to all other pleurostomatids and thus represents an independent lineage and a separate family, Protolitonotidae fam. n., which is defined by the presence of a semi‐suture formed by the right somatic kineties near the dorsal margin of the body; (ii) the families Litonotidae and Kentrophyllidae are both monophyletic based on both SSU rDNA and LSU rDNA sequences, whereas Amphileptidae are non‐monophyletic in trees inferred from SSU rDNA sequences; and (iii) the genera Loxophyllum and Kentrophyllum are both monophyletic, whereas Litonotus is non‐monophyletic based on SSU rDNA analyses. ITS1‐5.8S‐ITS2 sequence data were used for the phylogenetic analyses of pleurostomatids for the first time; however, species relationships were less well resolved than in the SSU rDNA and LSU rDNA trees. In addition, a major revision to the classification of the order Pleurostomatida is suggested and a key to its families and genera is provided.     

Phylogeography and the origins of range disjunctions in a north temperate fish,the pygmy whitefish (Prosopium coulterii), inferred from mitochondrial and nuclear DNA sequence analysis

Aim To investigate the degree of phylogeographical divergence within pygmy whitefish (Prosopium coulterii) and to test hypotheses concerning the origin of disjunct populations within North America. Location North America from western Alaska to Lake Superior. Methods Mitochondrial (ATPase subunit VI) and nuclear (ITS‐1, ITS‐2) DNA sequence variation was assessed across the species’ North American range to test for the existence of distinct phylogeographical groupings of pygmy whitefish associated with known glacial refugia. Coalescent simulations of the mitochondrial DNA (mtDNA) data were used to test hypotheses of population structure. Results This species is composed of two monophyletic mitochondrial clades across its North American range. The two mtDNA clades differed by an average 3.3% nucleotide sequence divergence. These clades were also distinguished by ITS‐2, but the relationships among lineages were not resolved by the ITS‐1 analysis. Coalescent analyses rejected the null hypothesis of the current disjunct distributions being a result of fragmentation of a single widespread ancestral lineage across a variety of effective population sizes and divergence times. Main conclusions The current range disjunctions of pygmy whitefish in North America probably resulted from isolation, genetic divergence, and selective dispersal from at least two major Pleistocene glacial refugia: Beringia and Cascadia. More recent isolation and dispersal from an upper Mississippi refugium is suggested by relationships within one of the clades and by distributional evidence from co‐distributed species. The Beringian and Cascadian refugia have played major roles in the zoogeography of Nearctic temperate aquatics, but the roles of smaller refugia appear more variable among other species.     

Low, but Strongly Structured Mitochondrial DNA Diversity in Root Knot Nematodes (Meloidogyne)

Root-knot nematodes (genus Meloidogyne) have been the subject of recent and numerous studies of genetic variation because of the need to develop molecular diagnostics for the four globally distributed, parthenogenetic species that are significant agricultural pests. Our analysis of Meloidogyne mtDNA improves on previous studies: (i) by examining restriction site polymorphism among a large number of isolates also characterized for standard morphological, host range and allozyme phenotypes; (ii) by using higher resolution electrophoretic techniques; and (iii) by mapping variable restriction sites with reference to the complete nucleotide sequence. This revealed fivefold less sequence divergence (<0.6%) between variants than estimated in previous restriction fragment length polymorphism (RFLP) studies, but perfect correspondence between mtDNA haplotype and allozyme (esterase) phenotypes. The mtDNA variation, although limited, is strongly structured with as much divergence between two lineages of Meloidogyne arenaria as between either of these and Meloidogyne javanica. The low diversity of mtDNAs suggests that these parthenogenetic lineages arose from distinct but closely related sexual females, a pattern seen in other parthenogenetic complexes. In contrast to the concordance between mtDNA and allozyme markers, there were several discrepancies between the traditional methods of identification. We suggest that further studies of these nematodes should focus on well defined genetic groups, whether or not these coincide with existing taxonomic units.     

Paleoclimatic history and vicariant speciation in the "sand goby" group (Gobiidae, Teleostei)

Vicariant and climatic cycling speciation hypotheses of the 'sand gobies' belonging to the genera Pomatoschistus, Gobiusculus, Knipowitschia, and Economidichthys are tested using molecular phylogenies constructed of nuclear DNA (ITS1 locus) and mitochondrial DNA (12S and 16S fragments). These gobies are among the most abundant in the Eastern Atlantic-Mediterranean region, and play an important role in the ecosystem. Considerable ITS1 length differences, primarily due to the presence of several tandem repeats, were found between species and even within individuals. Therefore, phylogenetic analyses focused on fragments of the 12S and 16S mtDNA region that have been sequenced for 16 goby taxa. The 'sand gobies' clustered as a monophyletic group as proposed on morphological grounds. However, G. flavescens, E. pygmaeus, and K. punctatissima clustered within the Pomatoschistus species, pointing to a paraphyletic origin of these genera. Furthermore, the genetic divergence between P. minutus from the Adriatic Sea versus the Atlantic-Mediterranean region was as high as the divergence within the P. minutus complex, suggesting that P. minutus from the Adriatic Sea should be considered as a distinct species. The "star" phylogeny might suggest that these gobies evolved in a very short time period, possibly linked to the drastic alterations in the Mediterranean Sea during and immediately after the Messinian salinity crisis at the end of the Miocene. The freshwater life-style appeared monophyletic; equating its origin with the salinity crisis resulted in a molecular clock estimate of 1.4% divergence per million years. The last common ancestor probably occupied sandy bottoms and a coastal niche while several species subsequently adapted to new habitats (pelagic, freshwater or stenohaline). The origin of the shallowest clades dated back to the glacial cycling during the Pleistocene epoch.