Rare and asymmetrical hybridization of the endemic Barbus carpathicus with its widespread congener Barbus barbus

In endemic species that co-occur with widespread congeners, hybridization can lead to an influx of novel and beneficial genetic variation, but high rates of introgression may cause genetic swamping of the endemic species and have detrimental effects on its survival potential. This study examines hybridization between sympatric populations of the Carpathian barbel Barbus carpathicus , a recently discovered cryptic species with a restricted range, and the widespread common barbel Barbus barbus . Based on six diagnostic allozyme loci, a microsatellite locus and mtDNA, hybrids were found to be present at multiple localities within the Vistula River drainage (Baltic Sea) as well as in the Tisza River system of the Danube River drainage (Black Sea). However, the numbers of hybrids were very low; four individuals of 230 fish sampled from the Vistula drainage. Bayesian assessment of their nuclear genotypes suggested that two hybrids in the Vistula drainage and nine in the Tisza system were F₁ generation, and one in the Vistula drainage and one in the Tisza system were backcrosses (BC) to B. barbus , while no F₂ or BC to B. carpathicus were detected. No hybrid carried B. carpathicus mtDNA and cytonuclear linkage disequilibria showed significant positive associations between hybrid genotypes and B. barbus mtDNA, suggesting unidirectionality in the interspecific mating with a disproportionate contribution of B. barbus mothers. Despite geographically broad occurrence of hybrids, these data provide evidence of strong constraints on hybridization in the native breeding habitats and the lack of introgression towards B. carpathicus .     

The North Mediterranean Barbus lineage: phylogenetic hypotheses and taxonomic implications based on allozyme data

On the basis of distinct ecological and morphological characters, the European Barbus taxa have been clustered in two groups: a fluvio-lacustrine and a rheophilic or strictly riverine one. These two groups (or ecophenotypes) were recognized in different parts of Europe, and formed either a species assemblage ( Barbus barbus group) or a polytypic species ( Barbus meridionalis ). The hypothesis was that species of the same group belong to the same phylogenetic lineage (clade) and are the result of the same transcontinental colonization event. The analysis, using allozyme markers, of 10 taxa of the genus Barbus from France, Italy, Greece, the Czech Republic and Slovakia, showed that the taxa thought to belong to the fluvio-lacustrine and the rheophilic groups are not monophyletic. The results suggest that probably in each sub-region, the founding taxon has diverged independently to form species of two different ecophenotypes, one occupying the upstream rivers and the other the lowland rivers. Accordingly, Barbus species groups represent clusters of morphologically convergent taxa living in equivalent biotopes.     

Natural hybridization of two species of tetraploid barbels: Barbus meridionalis and Barbus barbus (Osteichtyes, Cyprinidae) in southern France

Natural hybridization of Barbus barbus and B. meridionalis has been demonstrated in southern France. A genetical study (isozyme electrophoresis) of these species and their hybrids revealed the characteristics of hybridization. Ten enzyme markers and five morphological parameters were used to distinguish between the two parent species. Enzymatic divergence between the parent species included fixed allelic differences at certain loci and reduction in enzymatic activity, including the silencing of certain genes. A morphological study revealed a good correlation between the isozyme markers and morphological characters. Backcrosses were observed and this raises the question of the integrity of the parent species.     

A behavioural study of hybridization between Barbus barbus and Barbus meridionalis

The reproductive behaviour of two species of barbel ( Barbus barbus and Barbus meridionalis ) was investigated by means of aquarium experiments in several matings of six combinations. The reproductive behaviour of the two species appears to be similar and hybridizations were observed, showing that no complete behavioural barrier blocks the mating of the two species.     

HYBRID ZONES AND HOST-PARASITE RELATIONSHIPS: EFFECT ON THE EVOLUTION OF PARASITIC SPECIFICITY

In southern France, Diplozoon gracile (Monogenea, Polyopisthocotylea), parasitizes four sympatric cyprinids. One of these host species, Barbus meridionalis, naturally hybridizes with another species of barbel, Barbus barbus, which is never parasitized by D. gracile under natural conditions. This hybridization has previously been studied and described as an introgression of B. barbus by B. meridionalis. The hybrids are parasitized by D. gracile, and parasite prevalence increases in proportion to the introgression rate, i.e., the percentage of B. meridionalis genes. The causes for this preferential distribution of the parasite in the hybrid population are analysed on the basis of ecological and ethological differences between the two parent species.     

Spatially varying natural selection in a fish hybrid zone

A capture-mark-recapture (CMR) study in a hybrid zone between two species of barbel, Barbus barbus and Barbus meridionalis , in the Lergue River (southern France) failed to reject the null hypothesis of no difference in survival among phenotypes. Power calculations indicated that very intensive fieldwork should be carried out if this hypothesis was to be investigated again. The study demonstrated, however, that there were marked differences in survival between upstream and downstream sites. It is suggested that there is an environmental gradient of selection along the hybrid zone (extrinsic component of natural selection).     

Polymorphism of white muscle myosin and parvalbumins in the genus Barbus (Teleostei: Cyprinidae)

Muscle proteins were investigated in two large European barbels, Barbus barbus and B. meridionalis , and in four small tropical barbels native to SE Asia: B. conchonius , B. tetrazona , B. sachsi and B. titteya . Polyacrylamide gel electrophoresis was used to analyse myosin heavy and light chains and parvalbumin isotypes from white trunk muscle. Each species could be biochemically identified. The myosin subunit and parvalbumin isotype patterns obtained for the two European barbels were similar. The Asian barbels, on the other hand, not only differed from the European species but displayed a greater diversity within their group. These biochemical results are largely in agreement with morphological and genetic data, but fail to substantiate suggested close relationships between Asian barbel species.     

Haplotype diversity and phylogenetic relationships among the Iberian barbels (Barbus,Cyprinidae) reveal two evolutionary lineages

The phylogenetic relationships and haplotype diversity of all Iberian barbels were examined by analyzing the complete mitochondrial cytochrome b gene sequence (1141 bp) of 72 specimens from 59 Iberian localities. Phylogenetic findings demonstrated a clear distinction between two mitochondrial lineages and confirmed the existence of two previously considered subgenera: Barbus and Luciobarbus: The first subgenus, Barbus, is represented on the Iberian Peninsula by Barbus haasi and Barbus meridionalis. The second subgenus, Luciobarbus, includes the remaining endemic Iberian species: Barbus comizo, Barbus bocagei, Barbus microcephalus, Barbus sclateri, Barbus guiraonis, and Barbus graellsii. Mean haplotype divergence between these subgenera was 10.40%, providing evidence of a clear subdivision within the Iberian barbels. Our results conflict with those reported in a recent study, based on 307 cytochrome b base pairs, that failed to identify any division within the genus Barbus in the Iberian Peninsula. The inclusion of nine further species belonging to this genus (used as outgroups) allowed us to establish a closer relationship of the Iberian species of the subgenus Barbus with other European taxa than with the Iberian Luciobarbus, which was found to cluster with North African, Caucasian, and Greek species. At the population level, no biogeographic structure was shown by specimens of each species (only 5.98% of the variation was attributable to differences among populations of each species). Given the discrete amount of divergence found among the Luciobarbus species, the formation of current hydrographic basins during the Plio-Pleistocene seems to have played a major role in their isolation and evolution.     

A population study of Barbus barbus (L.) in the River Severn, England

The results of the application of Schnabel (Chapman modification), Schumacher & Eschmeyer, Fisher & Ford, and Jolly capture-recapture techniques on the Barbus barbus (L.) population in four areas of the middle Severn are compared. The survival of tagged fish varied in different areas and fish released in some time periods were less vulnerable to recapture than fish released from other samples. It is suggested that the shoaling behaviour of Barbus barbus resulted in non-random mixing of marked fish. The average population size of Barbus barbus greater than 18 cm in length in each of the four sections for the total period of investigation gave population densities ranging from 0.024/m² to 0.202/m².     

Phylogeny and evolution of the genus Barbus in the Iberian Peninsula as revealed by allozyme electrophoresis

Variation of 14 enzyme systems encoded by 31 presumptive loci in different barbel species was studied using starch gel electrophoresis. Eighteen samples representing 11 Barbus tetraploid taxa were taken, including 10 populations from the Iberian Peninsula, six from other parts of western and southern Europe, one from northern Africa and one diploid species as outgroup from Asia Minor. The genetic analysis reassessed of the taxonomic status of the Iberian barbels into two distinct species groups. The first group included B. bocagei, B. comiza, B. graellsii, B. gulraonis, B. microcephalus , and B. sclateri , that aligned with B. callensis from northern Africa and with B. apoensis from Asia Minor; the other group included B. haasi and B. merldlonahs that was related to the European species, B. barbus, B. plebejus and B. peloponnesius . These groups are probably not monophyletic. It is suggested that the isolation of the Iberian Peninsula from Europe since the Oligocene-Miocene may explain the genetic affinities of the Iberian barbels with those of North African rather than with the European group.     

Morphological and biometric comparison of the scales of the barbels (Barbus cuvier) of Spain

The scales of 386 specimens of the eight species of the genus Barbus present in Spain (B. bocagei, B. comiza, B. graellsii, B. guiraonis, B. haasi, B. meridionalis, B. microcephalus, and B. sclateri) were studied. Six scales were extracted from each specimen, measurements taken, and the number of radii noted. Indices were obtained from these data. Statistical analysis allowed two groups to be established: 1) B. meridionalis and B. haasi, living in the upper stretches of rivers and distributed in the north of Spain; and 2) the remaining species. Within both groups a latitudinal gradation in the elongation of the scales and in the proportion of radii of the lateral fields was observed.     

Biogeography and pattern of gene flow among Barbus species (Teleostei: Cyprinidae) inhabiting the Italian Peninsula and neighbouring Adriatic drainages as revealed by allozyme and mitochondrial sequence data

Genetic relationships among 24 Italian and Adriatic populations of barbs (genus Barbus ) were assessed using electrophoretic analysis of allozymes and mitochondrial DNA sequences of the cytochrome b gene. Results obtained with both markers were concordant, but they were not congruent with the current morphology-based systematics and taxonomy. Populations assigned to the same nominal taxa ( B. caninus , B. petenyi and B. rebeli ), were very divergent in both allozymes and mtDNA, indicating that these populations deserve recognition as different units for conservation and management. On the other hand, the two fluvio-lacustrine taxa considered as distinct species (i.e. B. plebejus and B. tyberinus ) are genetically very close to each other, showing no clear differences at either allozymes or mtDNA. The population of B. caninus from Pellice River carried allozyme alleles and mtDNA specific for B. plebejus , indicating a genetic introgression towards the former species. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 83–99.     

Hybridization between two parapatric ranid frog species in the northern Sierra Nevada,California, USA

Contact zones between species provide a unique opportunity to test whether taxa can hybridize or not. Cross‐breeding or hybridization between closely related taxa can promote gene flow (introgression) between species, adaptation, or even speciation. Though hybridization events may be short‐lived and difficult to detect in the field, genetic data can provide information about the level of introgression between closely related taxa. Hybridization can promote introgression between species, which may be an important evolutionary mechanism for either homogenization (reversing initial divergence between species) or reproductive isolation (potentially leading to speciation). Here, we used thousands of genetic markers from nuclear DNA to detect hybridization between two parapatric frog species (Rana boylii and Rana sierrae) in the Sierra Nevada of California. Based on principal components analysis, admixture, and analysis of heterozygosity at species diagnostic SNPs, we detected two F1 hybrid individuals in the Feather River basin, as well as a weak signal of introgression and gene flow between the frog species compared with frog populations from two other adjacent watersheds. This study provides the first documentation of hybridization and introgression between these two species, which are of conservation concern.     

Combining geometric morphometrics with molecular genetics to investigate a putative hybrid complex: a case study with barbels Barbus spp. (Teleostei: Cyprinidae)

This integrative study examined the morphological and genetic affinities of three endemic barbel species from Italy (brook barbel Barbus caninus, Italian barbel Barbus plebejus and horse barbel Barbus tyberinus) and of putative hybrid specimens to their species of origin. Two of the species frequently occur together with the non‐native barbel Barbus barbus. DNA barcoding indicates that mitochondrial (mt) haplotypes often do not match the species expected from morphology. Linear distance measurements and meristics are not informative for discrimination of the species and putative hybrids, but a discriminant analysis of principal components (DAPC) of geometric landmark data produces reassignments largely in congruence with mt and nuclear genetic data. Cyto‐nuclear conflicts confirm the presence of hybridization in B. plebejus and B. tyberinus and identify additional introgressed specimens. A comparison between mixed genotypes and their morphology‐based assignment reveals no predictable pattern. The finding that most individuals of the morphologically similar B. plebejus and B. tyberinus have very high assignment probabilities to their respective species suggests that the presented approach may serve as a valuable tool to distinguish morphologically very similar taxa.     

Morphological changes of the nucleolus during oogenesis in oviparous teleost fish, Barbus barbus (L.)

In fishes, like in amphibians, it is well established that variations in rRNA activity occur during oogenesis. Contrary to amphibians, however, little is known about the ultrastructural changes of the nucleolus during fish oogenesis. Evolution of the nucleolus has been followed during oogenesis in the teleost fish Barbus barbus (L.) using light and transmission electron microscopies. We show that the behaviour of the nucleolus during B. barbus oogenesis resembles that reported in amphibians but also presents several peculiarities. The most striking feature is the marked vacuolization of nucleoli occurs at the beginning of the growth during previtellogenesis. The results obtained by means of the in situ terminal deoxynucleotidyl transferase-immunogold method for detecting DNA seem further to indicate that the chromatin cap becomes integrated into developing nucleoli during previtellogenesis and then segregate at the periphery of nucleoli at the end of glycoproteinic vitellogenesis. Our study also shows that the nucleoli of germ cells, like that of follicle cells, are devoid of fibrillar centre but comprise a fibrillar and a granular component whatever the oogenetic stage. Ultrastructural detection of DNA and nucleolar proteins (AgNOR proteins, fibrillarin, and pp135) supports further the view that the Barbus nucleolus is a bipartite structure.     

Genomic markers reveal introgressive hybridization in the Indo-West Pacific mangroves: a case study

Biodiversity of mangrove ecosystems is difficult to assess, at least partly due to lack of genetic verification of morphology-based documentation of species. Natural hybridization, on the one hand, plays an important role in evolution as a source of novel gene combinations and a mechanism of speciation. However, on the other hand, recurrent introgression allows gene flow between species and could reverse the process of genetic differentiation among populations required for speciation. To understand the dynamic evolutionary consequences of hybridization, this study examines genomic structure of hybrids and parental species at the population level. In the Indo-West Pacific, Bruguiera is one of the dominant mangrove genera and species ranges overlap extensively with one another. Morphological intermediates between sympatric Bruguiera gymnorrhiza and Bruguiera sexangula have been reported as a variety of B. sexangula or a new hybrid species, B. × rhynchopetala. However, the direction of hybridization and extent of introgression are unclear. A large number of species-specific inter-simple sequence repeat (ISSR) markers were found in B. gymnorrhiza and B. sexangula, and the additive ISSR profiling of B. × rhynchopetala ascertained its hybrid status and identified its parental origin. The varying degree of scatterness among hybrid individuals in Principal Coordinate Analysis and results from NewHybrids analysis indicate that B. × rhynchopetala comprises different generations of introgressants in addition to F(1)s. High genetic relatedness between B. × rhynchopetala and B. gymnorrhiza based on nuclear and chloroplast sequences suggests preferential hybrid backcrosses to B. gymnorrhiza. We conclude that B. × rhynchopetala has not evolved into an incipient hybrid species, and its persistence can be explained by recurrent hybridization and introgression. Genomic data provide insights into the hybridization dynamics of mangrove plants. Such information can assist in biodiversity assessment by helping detect novel taxa and/or define species boundaries.     

A novel functional class I lineage in zebrafish (Danio rerio), carp (Cyprinus carpio), and large barbus (Barbus intermedius) showing an unusual conservation of the peptide binding domains

Species from all major jawed vertebrate taxa possess linked polymorphic class I and II genes located in an MHC. The bony fish are exceptional with class I and II genes located on different linkage groups. Zebrafish (Danio rerio), common carp (Cyprinus carpio), and barbus (Barbus intermedius) represent highly divergent cyprinid genera. The genera Danio and Cyprinus diverged 50 million years ago, while Cyprinus and Barbus separated 30 million years ago. In this study, we report the first complete protein-coding class I ZE lineage cDNA sequences with high similarity between the three cyprinid species. Two unique complete protein-coding cDNA sequences were isolated in zebrafish, Dare-ZE*0101 and Dare-ZE*0102, one in common carp, Cyca-ZE*0101, and six in barbus, Bain-ZE*0101, Bain-ZE*0102, Bain-ZE*0201, Bain-ZE*0301, Bain-ZE*0401, and Bain-ZE*0402. Deduced amino acid sequences indicate that these sequences encode bonafide class I proteins. In addition, the presence of conserved potential peptide anchoring residues, exon-intron organization, ubiquitous expression, and polymorphism generated by positive selection on putative peptide binding residues support a classical nature of class I ZE lineage genes. Phylogenetic analyses revealed clustering of the ZE lineage clade with nonclassical cyprinid class I Z lineage clade away from classical cyprinid class I genes, suggesting a common ancestor of these nonclassical genes as observed for mammalian class I genes. Data strongly support the classical nature of these ZE lineage genes that evolved in a trans-species fashion with lineages being maintained for up to 100 million years as estimated by divergence time calculations.     

Thermal related variations of seasonal and daily spawning periodicity in Barbus barbus

In 1993, nocturnal spawning activities were observed in the diurnal spawning cyprinid Barbus barbus . This behaviour is interpreted as a response to exceptionally high daily thermal amplitudes, regarded as the sign of an unpredictable environment.     

Asymmetric introgression between fishes in the Red River basin of Texas is associated with variation in water quality

When ecologically divergent taxa encounter one another, hybrid zones can form when reproductive isolation is incomplete. The location of such hybrid zones can be influenced by environmental variables, and an ecological context can provide unique insights into the mechanisms by which species diverge and are maintained. Two ecologically differentiated species of small benthic fishes, the endemic and imperiled prairie chub, Macrhybopsis australis, and the shoal chub, Macrhybopsis hyostoma, are locally sympatric within the upper Red River Basin of Texas. We integrated population genomic data and environmental data to investigate species divergence and the maintenance of species boundaries in these two species. We found evidence of advanced‐generation asymmetric hybridization and introgression, with shoal chub alleles introgressing more frequently into prairie chubs than the reciprocal. Using a Bayesian Genomic Cline framework, patterns of genomic introgression were revealed to be quite heterogeneous, yet shoal chub alleles were found to have likely selectively introgressed across species boundaries significantly more often than prairie chub alleles, potentially explaining some of the observed asymmetry in hybridization. These patterns were remarkably consistent across two sampled geographic regions of hybridization. Several environmental variables were found to significantly predict individual admixture, suggesting ecological isolation might maintain species boundaries.