Phenetic relationships and probable ways of morphological diversification of the African large barbs (<Emphasis Type="Italic">Barbus intermedius</Emphasis> complex) in Lake Tana (Ethiopia)

29 quantitative and 18 qualitative skull characters were studied in the African large barbs (Barbus intermedius complex) from Lake Tana (Ethiopia). Based on results of principle components analysis phenetic relationships of 12 morphotypes were assessed. External features diagnostic of the morphotypes were found in individuals substantially different in the skull characters. The obtained data along with the data on morphological diversity of large barbs from Ethiopia beyond the Lake Tana basin suggest origination of the Lake Tana complex of forms from a complex of forms that existed in the upper reaches of the Blue Nile before the lake came into being, and the extant morphotypes of the Lake Tana barbs originated from three or four forms that composed the ancestral riverine local complex.     

Lake Tana large barbs: phenetics, growth and diversification

Among the Lake Tana large barbs of about 10 cm SL only representatives of the' acute'morphotype can be distinguished, in the size range 10–20 cm SL' bigmouth big eye' can be identified also. As for the rest, very few individuals can be confidently affiliated with a particular morphotype most of them looking like' intermedius'. Even within the range of 20–30 cm SL some individuals are still difficult to identify. Principal component analysis of cranial characters revealed discrete groups of morphotypes. Differences in both external and cranial characters of the morphotypes result from divergence which is most pronounced when fish are 4–5 years old and 20–25 cm SL. This divergence cannot be related exclusively with differences in the growth rates of individuals representing different morphotypes. Differences in food composition between the morphotypes probably increase in parallel with their morphological divergence. Differences between the morphotypes in the lateral line (11) and the gill rakers (Sb) counts were revealed using ANOVA. Comparison of the Lake Tana Barbus complex of forms with that previously known from Lake Lanao (Philippines) suggests that in both lakes the different forms arose sympatrically but that sympatric speciation in Lake Lanao has advanced further than in Lake Tana.     

Observations on reproduction of the Lake Tana barbs

During the rainy season (September–November 1994), in tributaries of Lake Tana (Ethiopia), the Gumara, Gelda and Negashu, barbs of diVerent morphotypes were ready to spawn, running and spent. The most numerous were barbs similar to Barbus intermedius common in many rivers of the Ethiopian Highlands. They were also found spawning in the Gumara and Gelda Rivers in the dry season (February 1996, 1997). There were no evident diVerences in time and place of spawning of barbs representing diVerent morphotypes. Only zurki, bigmouth mini-eye and bighead were not found in the rivers. Spatial and temporal segregation may contribute to reproductive isolation of morphotypes spawning in rivers, but if reproductive isolation exists the main role must be played by diVerences in mating behaviour. Morphotypes of the Lake Tana barbs have diVerent migration patterns. Barbs similar to the riverine B. intermedius may spend their lives in rivers or in the lake, moving to and fro. Barbs of acute, bigmouth big-eye and, perhaps, other morphotypes migrate downstream as alevins or fry, stay in the lake for several years and migrate back into rivers for spawning after reaching maturity.     

Speciation of endemic Lake Tana barbs (Cyprinidae, Ethiopia) driven by trophic resource partitioning; a molecular and ecomorphological approach

A unique species flock of large barbs (Barbus spp.) from Lake Tana is presented, from the level of fish stocks to molecules. Evidence is given for the species status of 14 morphotypes of large barbs. They distinctly differ in: (1) head and body morphometrics, (2) food preferences, (3) distribution patterns, (4) maximal body size, (5) spawning area and period, and (6) molecular genetic characters. Most types show early morphological divergence at small size. Major Histocompatibility Complex (MHC) genes, encoding cell membrane proteins involved in defence against pathogens, were found to be diagnostic for the species' genetic identity. A strong selective pressure on particular amino acid positions in the MHC protein sequence most probably arose in response to different pathogen loads from the newly invaded ecological niches after formation of Lake Tana, ca. two million years ago.Arguments for a sympatric origin of this species flock are discussed. An evolutionary scenario suggests a riverine ancestral Barbus intermedius invading Lake Tana after its formation by volcanic blocking of the Blue Nile river and its isolation by waterfalls. Specialisation for particular food types and disruptive selection on many feeding structures are hypothesized as the evolutionary drive in speciation. The causal relationship between the diversity in feeding structures and food types is explained from experiments and models. As an example, the potential food niche of three barb species is predicted from parameter values measured from a large set of feeding structures and tested against the actual gut contents. The co-occurrence of eight piscivorous barb species is unique for cyprinid fish, which lack oral jaw teeth and a stomach. The significance of this aquatic ecosystem as a multidisciplinary evolutionary laboratory and the need for a wise balance between exploitation and conservation is stressed.     

Major histocompatibility genes in the Lake Tana African large barb species flock: evidence for complete partitioning of class II B, but not class I, genes among different species

The 16 African large barb fish species of Lake Tana inhabit different ecological niches, exploit different food webs and have different temporal and spatial spawning patterns within the lake. This unique fish species flock is thought to be the result of adaptive radiation within the past 5 million years. Previous analyses of major histocompatibility class II B exon 2 sequences in four Lake Tana African large barb species revealed that these sequences are indeed under selection. No sharing of class II B alleles was observed among the four Lake Tana African large barb species. In this study we analysed the class II B exon 2 sequences of seven additional Lake Tana African large barb species and African large barbs from the Blue Nile and its tributaries. In addition, the presence and variability of major histocompatibility complex class I UA exon 3 sequences in six Lake Tana and Blue Nile African large barb species was analysed. Phylogenetic lineages are maintained by purifying or neutral selection on non-peptide binding regions. Class II B intron 1 and exon 2 sequences were not shared among the different Lake Tana African large barb species or with the riverine barb species. In contrast, identical class I UA exon 3 sequences were found both in the lacustrine and riverine barb species. Our analyses demonstrate complete partitioning of class II B alleles among Lake Tana African large barb species. In contrast, class I alleles remain for the large part shared among species. These different modes of evolution probably reflect the unlinked nature of major histocompatibility genes in teleost fishes.Electronic Supplementary Material Supplementary material is available for this article at .An erratum to this article can be found at     

Mitochondrial DNA phylogeography of the Labeobarbus intermedius complex (Pisces,Cyprinidae) from Ethiopia

Mitochondrial DNA phylogeography of populations of the Labeobarbus intermedius complex (hexaploid barb) was investigated using 88 complete and 71 partial cytochrome b (cytb) sequences originating from 21 localities in five major drainages in Ethiopia and two localities in northern Kenya. The samples included 14 of the 15 Labeobarbus species described from Lake Tana. Discrete phylogeographic analyses of 159 cytb sequences employing Bayesian Markov Chain Monte Carlo (MCMC) simulations using Bayesian evolutionary analysis by sampling trees (BEAST) supported the monophyly of the L. intermedius complex, including the Lake Tana species. This analysis, in combination with statistical parsimony analysis, identified two mitochondrial DNA lineages within the complex. Divergence dating employing coalescent simulations suggested that the geographic split in the L. intermedius complex that led to the formation of these lineages occurred during the Pleistocene (c. 0·5 M b.p. ), consistent with the timing of volcano‐tectonic events postulated to have shaped the current landscape of East Africa.     

Spawning of large <Emphasis Type="Italic">Barbus</Emphasis> (<Emphasis Type="Italic">Barbus intermedins</Emphasis> Complex) in a small river of the Lake Tana basin (Ethiopia) and relationships of some putative species

Direct observations on three forms (morph types) of spawning barbs, considered by some authors as different species, were carried out in September–October 2005 at the Gumara River and its small tributary, the Ducalit, in the Lake Tana basin. The spawning barbs were sampled using cast nets. Barbs of different morphotypes composed common spawning aggregations and were caught together. It is likely that troutlike females mate extensively with intermedius males and, probably, with bigmouth small-eye males. Experiments in artificial fertilization and rearing showed that, during the embryonic period, there was no increase in mortality of progeny from crosses of barbs of different morphotypes, in comparison with homonomic crosses, thus suggesting an absence of postzygotic reproductive isolation between the morphotypes. At the same time, mortality of progeny from crossing barbs with Varicorhinus beso Rüppell, 1836 was very high during the earliest stages of development, suggesting strong, even if incomplete, reproductive isolation ensured by postzygotic mechanisms. Published in Voprosy Ikhtiologii, 2007, Vol. 47, No. 5, pp. 676–683. The article was translated by the authors.     

Molecular characterisation and interpretation of genetic diversity within globally distributed germplasm collections of tall fescue (Festuca arundinacea Schreb.) and meadow fescue (F. pratensis Huds.)

Allohexaploid tall fescue (Festuca arundinacea Schreb. syn. Lolium arundinaceum [Schreb.] Darbysh.) is an agriculturally important grass cultivated for pasture and turf world-wide. Genetic improvement of tall fescue could benefit from the use of non-domesticated germplasm to diversify breeding populations through the incorporation of novel and superior allele content. However, such potential germplasm must first be characterised, as three major morphotypes (Continental, Mediterranean and rhizomatous) with varying degrees of hybrid interfertility are commonly described within this species. As hexaploid tall fescue is also a member of a polyploid species complex that contains tetraploid, octoploid and decaploid taxa, it is also possible that germplasm collections may have inadvertently sampled some of these sub-species. In this study, 1,040 accessions from the publicly available United States Department of Agriculture tall fescue and meadow fescue germplasm collections were investigated. Sequence of the chloroplast genome-located matK gene and the nuclear ribosomal DNA internal transcribed spacer (rDNA ITS) permitted attribution of accessions to the three previously known morphotypes and also revealed the presence of tall fescue sub-species of varying ploidy levels, as well as other closely related species. The majority of accessions were, however, identified as Continental hexaploid tall fescue. Analysis using 34 simple sequence repeat markers was able to further investigate the level of genetic diversity within each hexaploid tall fescue morphotype group. At least two genetically distinct sub-groups of Continental hexaploid tall fescue were identified which are probably associated with palaeogeographic range expansion of this morphotype. This work has comprehensively characterised a large and complex germplasm collection and has identified genetically diverse accessions which may potentially contribute valuable alleles at agronomic loci for tall fescue cultivar improvement programs.     

Searching for speciation genes: molecular evidence for selection associated with colour morphotypes in the Caribbean reef fish genus Hypoplectrus

Closely related species that show clear phenotypic divergence, but without obvious geographic barriers, can provide opportunities to study how diversification can occur when opportunities for allopatric speciation are limited. We examined genetic divergence in the coral reef fish genus Hypoplectrus (family: Serranidae), which comprises of 10-14 morphotypes that are distinguished solely by their distinct colour patterns, but which show little genetic differentiation. Our goal was to detect loci that show clear disequilibrium between morphotypes and across geographical locations. We conducted Amplified Fragment Length Polymorphism molecular analysis to quantify genetic differentiation among, and selection between, morphotypes. Three loci were consistently divergent beyond neutral expectations in repeated pair-wise morphotype comparisons using two different methods. These loci provide the first evidence for genes that may be associated with colour morphotype in the genus Hypoplectrus.     

Assessment of the role of chemoreception in the mate choice in barbs of the Barbus intermedius complex from Lake Tana, Ethiopia

The role of chemoreception in mate choice was studied in barbs of the complex Barbus intermedius from Lake Tana. It was found that chemical communication may be used in reproductive interactions of the barbs, and that males are responsible for the choice. Mature males tend to prefer ripe females and avoid both immature females and mature males, or are indifferent to them. It was shown that selectivity in mate choice by certain barb morphotypes could reduce the probability of interbreeding between different morphotypes, but not provide for reproductive isolation between them. It was hypothesized that the mate groups are finally formed as a result of direct interactions between potential partners, mediated by tactile reception or specific behavioral patterns.     

Phenetic diversity of the large barbs (Barbus intermedius complex sensu Banister) from the coastal zone of the Bahar Dar Gulf (Lake Tana, Ethiopia)

Phenetic structure of a sample of large African barbs Barbus intermedius complex) taken in November 2010 from the inshore part of the Bahar Dar Gulf (Lake Tana) was studied. Principal components analysis was performed on 28 indices characterizing skull proportions and shape of bones. The individuals under study formed distinct clusters in the principal component space. Composition of these clusters was considered. Many morphotypes described in the 1990s were absent in the sample taken in 2010, and there were individuals which did not comply with the diagnoses of the previously described morphotypes. It was suggested that some of these fish represented phenetic groups which did not occur in the offshore part of the gulf, some were, most probably, hybrids of the known morphotypes or originated from homonomic crossings but did not had diagnostic characters of the parental morphotype.     

Reproductive segregation among the Barbus intermedius complex of Lake Tana,Ethiopia. An example of intralacustrine speciation?

Reproductive segregation among the large barbs Barbus intermedius complex, Cyprinidae , of Lake Tana, Ethiopia, was investigated in the mouths and upstream reaches of rivers tributary to the lake, during the spawning seasons of 1993 and 1994. The percentage of running fish of four Barbus morphotypes [Acute (Ac), Bigmouth big-eye (Be), Intermedius (In), and Shorthead (Sh)] peaks with the highest water level of the lake. Large differences are apparent in the minimum fork length of running fish among morphotypes [c. 12 cm for male Sh and 28 cm for male Bigmouth small-eye (Se)]. Significant differences occur in temporal, but especially in spatial patterns of the relative abundance of running morphotypes, when the lake is compared with the four major river mouths and their upstream reaches. These different relative abundances are clearest among Ac, Be, In, Sh and Troutlike (Tr). Also, the absence from the rivers of some morphotypes that are usually abundant in the lake itself [Barbel (Ba), Dark (Da), Lip (Li), and Zurki (Zu)], and the abundant presence in the rivers of Tr, rare in the lake, strengthen the hypothesis that spatial and/or temporal spawning segregation is present among the morphotypes. There are indications that Bighead (Bh) and Zu spawn in the lake itself, while other morphotypes were only found running in or near rivers. Combined with the morphological, ecological, and genetic differences, these data suggest the existence of several Barbus species, forming a unique species flock, which probably evolved within the lake. The presence of several, instead of one Barbus species complicates management of sustainable fisheries and protection of the lake's biodiversity. Present results show the importance of the rivers for Barbus reproduction and stress the urgent need for careful management of fishing activities in spawning times and areas.     

Changes of Skull Proportions in Ontogeny of Barbus canis from Lake Kinneret and of the Lake Tana large-mouthed barbs, Barbus intermedius Complex

Skull proportions of Barbus canis individuals drastically change during their life. Yearlings have skull proportions characteristic for barbs of the NEC phenetic group (sensu Mina et al. 2001 Environ. Biol. Fish. 61: 242–252), but with age become similar to those of the Lake Tana large-mouthed morphotypes which acquire their specific features at 3–7 years old while at earlier ages they have skull proportions of a NEC form identified as 'intermedius' sensu Nagelkerke et al. (1994 Environ. Biol. Fish. 39: 1–21). The large-mouthed Lake Tana barbs originated from an ancestral NEC form through peramorphosis, but in relation to B. canis they are paedomorphic in skull proportions. B. canis supposedly originated from a NEC form as a consequence of an adaptive radiation that took place in western Asia.     

Shallow genetic divergence and species delineations in the endemic Labeobarbus species flock of Lake Tana,Ethiopia

To assess whether the species distinctions of Lake Tana's Labeobarbus spp. are supported by genetic information, microsatellite markers were used. A total of 376 Labeobarbus spp., belonging to 24 populations of 11 species from three regions of the lake (north, south and east), were sampled. Eight microsatellite markers were analysed. In general, differences between conspecific populations were smaller than differences between populations of different species. For six species, conspecific populations from different regions in the lake were consistently more similar than populations of other species from the same region. For four species this was not the case, while for one species two populations were similar, but different from the third population. River‐spawning species appeared to be more distinct than presumed lake spawners. On the species level, there was a significant correlation between genetic and morphological differentiation, especially in morphological aspects associated with ecological functioning. This suggests that genetic differentiation arose together with adaptive radiation, although the overall genetic differentiation among the Lake Tana Labeobarbus spp. is small.     

Individual ontogenetic trajectories and ontogenetic channels of three forms of large African barbs (<Emphasis Type="Italic">Barbus intermedius</Emphasis> complex). Analysis of experimental data

Changes of external morphological characters in three forms (morphotypes) of African barbs from Lake Tana (Ethiopia) belonging to Barbus intermedius complex were traced using electronic tags. It was shown that within age interval from two to four years individual ontogenetic allometric curves often cannot be described with a single power function equation. Individual ontogenetic trajectories in the principal components space within this interval strongly differ in shape meandering within ontogenetic channels outlined on the basis of cross-sectional data. Morphological differences between siblings are found that do not allow to classify some of them with the morphotype of their parents.     

SPECIES FLOCK IN THE NORTH AMERICAN GREAT LAKES: MOLECULAR ECOLOGY OF LAKE NIPIGON CISCOES (TELEOSTEI: COREGONIDAE: COREGONUS)

Studies on north temperate fish species indicate that new habitat availability following the last ice sheet retreat has promoted ecological speciation in postglacial lakes. Extensive ecophenotypic polymorphisms observed among the North American Great Lakes ciscoes suggest that this fish group has radiated through trophic adaptation and reproductive isolation. This study aims at relating the ecomorphological and genetic polymorphisms expressed by the Lake Nipigon ciscoes to evaluate the likelihood of an intralacustrine divergence driven by the exploitation of alternative resources. Morphological variation and trophic and spatial niches are characterized and contrasted among 203 individuals. Genetic variation at six microsatellite loci is also analyzed to appraise the extent of genetic differentiation among these morphotypes. Ecomorphological data confirm the existence of four distinct morphotypes displaying various levels of trophic and depth niche overlap and specialization. However, ecological and morphological variations were not coupled as expected, suggesting that trophic morphology is not always predictive of ecology. Although extensive genetic variability was observed, little genetic differentiation was found among morphotypes, with only one morph being slightly but significantly differentiated. Contrasting patterns of morphological, ecological, and genetic polymorphisms did not support the hypothesis of ecological speciation: the most ecologically different forms were morphologically most similar, while the only genetically differentiated morph was the least ecologically specialized. The low levels of genetic differentiation and the congruence between θ and φ estimates altogether suggest a recent (most likely postglacial) process of divergence and/or high gene flow among morphs A, C, and D, whereas higher φ estimates for comparison involving morph B suggest that this morph may be derived from another colonizing lineage exchanging little genes with the other morphs. Patterns of ecophenotypic and genetic diversity are also compatible with a more complex evolutionary history involving hybridization and introgression.     

Impact of rifting and hydrography on the genetic structure of Clarias gariepinus in eastern Africa

In a study of the genetic structure of Clarias gariepinus at the ND5 and ND6 loci of mitochondrial DNA using RFLP–PCR in 16 populations (267 fish), a total of 18 haplotypes was detected. The most common haplotype was EA1 and represented 46% of all genotypes. Three phylogenetic groups characterized the region, with the East African clade occurring between the western rift in the west, Lake Baringo in the north, the Indian Ocean in the east and the Rufiji River in the south. The Lower Tana River (unlike the Upper Tana River) and Lake Kamnarok grouped with the North clade, while the Ruaha River (tributary of the Rufiji River) represented a contact zone between the East and the South-central African clade. Genetic structure was distinct ( F _ST=0·66), with the Lower Tana River and Lake Mtera forming specific units. Within the East clade, the Oloibortoto River, Upper Tana River and Lake Victoria each formed a distinct population. Lake Baringo grouped either with the eastern rift or the western rift depending on the analysis. Lake Jipe, the Pangani River, Rusizi River, Lake Edward, Nyabugogo River and the Luiche River clustered together. Among group variance explained 66·8% of the total variance; the impact of vicariance (rifting and uplifting) on the phylogeography was considerable. A distribution model of the catfish is proposed which combines the separation by rifting several million years ago with a high gene flow in the western rift due to historical connectivity among lakes and rivers.     

Toothless predators: feeding performance and techniques among the piscivores within Lake Tana's endemic barbus species flock (Pisces:Cyprinidae)

With more than 2000 fish species the Cyprinidae is the largest family of vertebrates. Lake Tana, a large lake (3050 km²) situated in the NW‐ highlands of Ethiopia, harbours, as far as we know the only remaining intact species flock of large (max. 100 cm FL) cyprinid fishes (15 Barbus spp.). One of the most intriguing aspects of this endemic Barbus species flock is the large number of piscivores (8). Cyprinid fishes seem not well designed for piscivory, they lack teeth in the oral jaw, have a small slit‐shaped pharyngeal cavity and all lack a stomach with low pH for digesting large prey. Many barbs are benthivorous species, like the ancestral barb in Lake Tana's isolated system. Why then is piscivory, which is rare among cyprinids, so common in Lake Tana Barbus? The aim of present study was to compare the performance and techniques of these piscivorous Barbus with known piscivores from other fish families. We studied prey handling times over prey size, prey capture using high‐speed movies, and assessed the effect of prey size on performance and prey selection in the field. Performances were explained by functional morphology of their feeding system. Overall, Lake Tana's piscivorous Barbus perform relatively 'poor', compared to piscivores from other fish families. For example, Lake Tana's piscivores are only able to handle prey fish smaller than 16% of their own body length. However, Lake Tana lacks potential piscivorous competitors, rendering the piscivorous Barbus by far the 'best' and apparently highly successful. They have adapted to all available macro‐habitats (littoral, offshore pelagic and offshore benthic), using different techniques (ambush, pursuit and cruising), a unique scenario for barbs.