ISSN:1125-0003    

DOI:10.1080/11250009809386787

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The Lake Tana (northern Ethiopia) ichthyofauna is dominated by ‘large’ barbs (Barbusspp., Cyprinidae). Recently, fourteenBar‐busmorphs have been described. This paper provides evidence that these morphs are indeed biological species. To investigate the hypothesis that disruptive selection on feeding‐related morphological characters was the evolutionary driving force of speci‐ation, an ecomorphological analysis, investigating the quantitative relationships between morphology and feeding abilities on a number of aquatic food types was investigated. The analysis accurately predicted the potential trophic niches of the Lake Tana barbs and supported the disruptive selection hypothesis. Finally, a hypothetical evolutionary scenario is presented in which disruptive selection led to initial morphological differentiation, and spatial and temporal spawning segregation stabilized the genetic differences among the morphs, resulting in speciation.

ISSN:1125-0003    

DOI:10.1080/11250009809386788

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In the Lake Tana barbs the PCA of skull measurements reveals “ontogenetic channels”; within which individual ontogenetic trajectories are located. Some individuals seem to acquire states of characters specific for a certain morphotype quite late when they are 20–25 cm SL and 3–5 years old. Morphologically different sympatric forms of large barbs are also found in the Didessa (Blue Nile basin), Genale (Wabi Shebeli basin), and Gibe (Omo basin) rivers. In all the three rivers barbs resembling certain morpho‐types of the Lake Tana barbs occur. Most probably, allopatric big‐mouthed forms originated independently from sympatric forms which have no conspicuous specific traits and that their similarity results from homoplasies.

ISSN:1125-0003    

DOI:10.1080/11250009809386789

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Cyprinid fishes assigned to the genusBarbusconstitute a poly‐phyletic assemblage that includes at least three different ploidy levels: diploid, tetraploid and hexaploid.’B. ‘ intermedius, inhabiting Lake Tana (Ethiopia), is a hexaploid taxon that forms a ‘species flock’ consisting of at least 14 morphotypes. The phenomenon is described in this review with reference to currently available cytogenetic and molecular genetic data. Cytogenetic data show that’B. ‘ intermediusis hexaploid both within and outside the Lake Tana basin. No chromosome banding analyses are currently available. Data based exclusively on conventionally Giemsa‐stained chromosomes suggest interpopulation variability. This should be confirmed using chromosome banding techniques. Major Histocompatibility Complex genes sequencing gave the first indication of genetic isolation of morphotypes. Allozymes have been analysed in a large sample of’B.’ intermedius.No diagnostic loci were observed in the’B.’ intermediusmorphotypes, but more or less important differences in allele frequencies were found. Only one morphotype, Acute, differs significantly from the others. The presence of this genetically differentiated morphotype in the lake strongly suggests that the morphotypes are diverging lineages. Because of some parallel characteristics with cichlid species flocks, we put forward the hypothesis that the barb morphotypes in Lake Tana represent a species flock that originated via sympatric speciation with more rapid morphological than cytogenetic and molecular differentiation. If the differentiation and the reproductive isolation (at least partial) are real, it is probable that the morphotypes already are and/or soon will reach the status of species.

ISSN:1125-0003    

DOI:10.1080/11250009809386790

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The characteristics of high population and species biodiversity, taken together with the major anthropogenic threats arising from exploitation, introductions and habitat alterations, have ensured that fishes have received major attention from molecular biologists in the study of wild populations. Foremost among the various challenges has been the development of techniques to estimate population discreteness and associated patterns of dispersal and gene flow, so‐called stock structure analysis. Here, we review some recent developments in molecular technology, especially microsatellite analysis, and consider critically how such markers can be employed to estimate genetic differentiation in species exhibiting high mobility in open waters. Comparisons are made between microsatellites and other genetic markers (protein and DNA) in their ability to detect population structuring. Particular emphasis is placed on the need to design sampling programmes that take account of aspects of the biology of the species under study, and the scale and nature of sample collection. Recent novel applications of PCR‐based technology in the analysis of population structure are considered, including the detection of micro‐geographic differentiation, the analysis of historical fish populations using recovered DNA, and the molecular characterization of allelic variants among populations in relation to function.

ISSN:1125-0003    

DOI:10.1080/11250009809386791

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The extent of genetic variation and its geographic structure as revealed by mitochondrial DNA (mtDNA) analysis are reviewed for five percid species. Walleye(Stizostedion vitreum)has been the most studied species and extensive polymorphism (42 haplotypes) was found in whole‐molecule RFLP studies, with significant geographic structure to the distribution of the haplotypes being largely related to Pleistocene glacial events. Analysis of whole‐molecule mtDNA with 4‐and 5‐base recognition restriction enzymes also revealed considerable variation which permitted the discrimination of individual fish from two central Great Lakes populations. DNA sequencing and PCR‐RFLP studies have also revealed high levels of mtDNA variation in walleye and provided better resolution of population‐level heterogeneity. In contrast, sauger(S. canadense)shows very little mtDNA variation (only five haplotypes) with little geographic structure to the haplotype distribution. There is also no clear geographic structure to mtDNA variation in yellow perch (Perca flavescens)where 15 haplotypes have been identified. Preliminary data for Eurasian perch(P. fluviatilis)(five haplotypes) and zander(S. lucioperca)(three haplotypes) reveal some mtDNA polymorphism in both species, but sample sizes are too small in both cases to make any statements about their geographic structure.

ISSN:1125-0003    

DOI:10.1080/11250009809386792

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Genetic variability was assessed in eight populations belonging to theLeuciscus soufflacomplex and in nine populations ofLeuciscus cephalus, sampled in France, Italy and Greece and in one population ofLeuciscus lucumonis, endemic to Italy. Twenty‐six enzymatic loci were analysed in order to clarify the genetic relationships, the patterns of colonisation of peri‐Mediterranean area and the taxonomic positions. Results indicate a more ancient penetration of theLeuciscus souffiacomplex in southern Europe (possibly during the Messinian ‘Lago Mare’ phase of the Mediterranean), whereasL. cephalusandL. lucumonisseem to have quite recently reached these regions (about 1Myr). These evidences are discussed in relation to the two main proposed models of primary freshwater fishes colonisation of peri‐Mediterranean area. In addition, the genetic distance suggests a generic separation between the two complexes. The genusTelestesBonaparte, is rehabilitated to include members of theLeuciscus souffiacomplex which is represented by endemic taxa from southern France, Italy and westem Balkans.

ISSN:1125-0003    

DOI:10.1080/11250009809386793

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Four hundred and twenty individual hake from 10 sample sites in the Mediterranean Sea were analysed in order to study genetic variability and identify genetic stock structure. Twenty loci were identified, four of which were polymorphic at the 95% level:ADH*, PGI‐1*, PGI‐2*andSOD‐1*.Average observed and expected heterozygosity were 0.084 and 0.090, respectively.PG1–1*deviated from Hardy‐Weinberg expectations due to an excess of heterozygotes and F‐statistic analysis showed also a significant excess of heterozygosity atSOD‐1*. FSTwas not significant for each locus except forPGI‐2*, where a single sample from the Channel of Sicily (C5) showed a different pattern in allelic frequencies, probably caused by a stochastic event. The samples analyzed seemed to be homogeneous, but future analyses may be necessary using other complementary molecular markers.

ISSN:1125-0003    

DOI:10.1080/11250009809386794

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Neotropical fishes present a high chromosome diversity showing a wide diploid number variation range, including different levels of ploidies, sex chromosomes, chromosome supernumeraries, and several cases of polymorphisms, related particularly to heterochromatin and NOR sites. Two main general trends of chromosome diversification can be observed among neotropical fishes. First, several fish groups show a chromosome evolution relatively divergent from the point of view of the karyotypic macrostructure. Sister species show conspicuous differences in karyotype structure and most often also in the number of chromosomes. On the other hand, there are fish groups in which chromosome evolution has been shown to be less divergent, and in this case whole families or even groups of families may share a common karyotype structure and equal number of chromosomes. Several fish groups appear conservative also with respect to the NOR bearing chromosomes. In this case, NOR chromosome location is invariable among species. In contrast, several other groups present wide NOR variability. Sister species may show quite diverse chromosomes bearing nucleolar organizing regions. The NOR and heterochromatin relationship is also very diverse among fishes and this may indicate organizational differences involving these chromosome segments. Thus, neotropical fish fauna presents great chromosome variability, verifiable also by NOR studies.

ISSN:1125-0003    

DOI:10.1080/11250009809386795

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The chromosomes of the two species of needlefish,Potamorraphiscf.eigenmanniandStrongylura microps, from fresh waters of Argentina were analyzed using C‐banding and silver staining and their karyotypes were described for the first time. The former species possessed 2n‐54 and karyotype composed of three pairs metacentric to submetacentric chromosomes and 24 pairs of subtelo to telocentric chromosomes. The NORs were situated on the end of the shorter arms of one middle‐sized bi‐armed pair of chromosomes. The later species possessed 2n=50 and karyotype composed exclusively of subtelo to telocentric chromosomes gradually decreasing in size. The NORs were situated inter‐stitially on the third pair of chromosomes. One or two supernumerary chromosomes were observed in one individual of the sample. Present data indicate greater cytotaxonomic diversity among species of needlefish which might be associated with their colonization of fresh waters.

ISSN:1125-0003    

DOI:10.1080/11250009809386796

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor