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.     

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.     

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.     

Genetic divergence among morphotypes of Lake Tana (Ethiopia) barbs

The genus Barbus is a paraphyletic assemblage that includes three different ploidy levels: diploid, tetraploid and hexaploid. 'B.' intermedins , which inhabits Lake Tana (Ethiopia), is a hexaploid taxon that forms a 'species flock' consisting of at least 14 morphotypes. Thirty-one presumptive allozymic loci were analysed in a large sample of 'B.' intermedius. No diagnostic loci were observed between the morphotypes, but substantial differences in allele frequencies were found. One morphotype, Acute, differs significantly from the others. The presence of this genetic differentiation within 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 morphotypes of barbs in Lake Tana represent a species flock that originated via sympatric speciation with more rapid morphological than molecular differentiation. If the differentiation and the reproductive isolation are real, it is probable that the morphotypes already are or will soon reach the status of species.     

Polymorphism of skull proportions in large African barbs <Emphasis Type="Italic">Barbus intermedius</Emphasis> sensu Banister (Cyprinidae) from Lakes Awasa and Langano (Rift Valley,Ethiopia)

After performing principal component analysis (PCA) of 13 characters (indices) of skulls of large African barbs (Barbus intermedius complex sensu Banister, 1973) from Lakes Awasa and Langano (Ethiopia) distributions of individuals in coordinates BL and PC1 were studied where BL is the basal skull length and PC1 is the first principal component. It is shown that in both the lakes there are groups of barbs whose individual ontogenetic trajectories are situated within separated ontogenetic channels. Separation of the channels is by far less distinct than that of the channels of generalized and specialized forms of barbs from Lake Tana and not correlated with differences in external traits. It is suggested that the revealed polymorphism is connected with food resource partitioning and might serve as a prerequisite of further divergence of sympatric forms of large African barbs.     

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.     

The status of Lake Lanao endemic cyprinids (Puntius species) and their conservation

The endemic cyprinid species flock of Lake Lanao, Philippines is a classic example of explosive evolution. Based on historical surveys, most of the 18 endemic cyprinid species in Lake Lanao are now believed to be extinct. We compared results of landing and market surveys conducted in 2008 to information from historical surveys. Field sampling and fishermen interviews provided additional information on the status of the endemic and other fish species in Lake Lanao. Puntius lindog and Puntius tumba were the only two endemic species recorded in 2008, accounting for 0.01 % and 0.04 % respectively of the total weight harvested. Our discovery that at least two endemic cyprinids remain in Lake Lanao is surprising and significant as the lake is increasingly imperiled by human disturbances, exploitation and introduced species. Protecting and conserving the remaining endemic species are important management priorities.     

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.     

Identification of the maternal source of young‐of‐the‐year Arctic charr in Lake Hazen,Canada

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Stock structure of Lake Baikal omul as determined by whole-body morphology

In Lake Baikal, three morphotypes of omul Coregonus autumnalis migratorius are recognized; the littoral, pelagic, and deep-water forms. Morphotype assignment is difficult, and similar to that encountered in pelagic and deep-water coregonines in the Laurentian Great Lakes. Principal component analysis revealed separation of all three morphotypes based on caudal peduncle length and depth, length and depth of the body between the dorsal and anal fin, and distance between the pectoral and the pelvic fins. Strong negative loadings were associated with head measurements. Omul of the same morphotype captured at different locations were classified to location of capture using step-wise discriminant function analysis. Jackknife correct classifications ranged from 43 to 78% for littoral omul from five locations, and 45–86% for pelagic omul from four locations. Patterns of location misclassification of littoral omul suggested that the sub-population structure, hence stock affinity, may be influenced by movements and intermixing of individuals among areas that are joined bathymetrically. Pelagic omul were more distinguishable by site and may support a previous hypothesis of a spawning-based rather than a foraging-based sub-population structure. Omul morphotypes may reflect adaptations to both ecological and local environmental conditions, and may have a genetic basis.     

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.     

Diversification, Sympatric Speciation, and Trophic Polymorphism of Arctic Charr, Salvelinus Alpinus Complex, in Transbaikalia

In northern Transbaikalia, independently evolving landlocked populations of Arctic charr are found in mountain lakes. To assess the diversity of charr in this region, speciation modes involved in the evolution of charr forms, and the role of trophic polymorphism in their divergence, we studied the morphology and feeding of dwarf, small, and large forms of Arctic charr from a number of Transbaikalian lakes. Meristic data on charr from five lakes support the earlier conclusion that the three forms do not represent separate lineages but have independently diverged in sympatry in each of the lakes. In 10 lakes, the dwarf form showed varying degrees of differentiation from normal (small and large) charr in meristic characters (up to morphologically distinct and presumably reproductively isolated groupings), which is viewed as various levels of sympatric divergence. Indexes of gill raker length in fish from 20 lakes vary among populations of both dwarf and normal charr, with forms having short and long rakers being sympatric in some of these lakes. However, the index can be used only for comparing charr of different forms up to about 32cm fork length (FL) because it is strongly negatively correlated with size in larger fish. The study of charr diets in 21 lakes indicates that large charr are piscivorous whereas dwarf and small charr feed on a wide range of invertebrates, partitioning these resources in different ways. Planktivores, including very specialized ones, and non-planktivores (benthic feeders, insectivores) can be identified within the small and dwarf forms. The proportion of plankton in the diets of dwarf and small charr is positively correlated with the number and length of gill rakers while the proportion of benthos is negatively correlated. Allopatric planktivorous and non-planktivorous small charr differ in body proportions; parallel emergence of such morphotypes in different parts of the range is a characteristic feature of the Salvelinus alpinus complex.     

Lake Tana large barbs diversity: Developmental and hormonal bases

Helerochronies caused by changes in the hormonal status are proposed to play a major role in the diversification of the Lake Tana barbs of Labeobarbus (=Barbus) genus (Dgebuadze and Mina, 2008). To test this hypothesis, we (i) compared temporal patterns of cranial development in L. intermedius, likely ancestral for Tana species flock, and L. brevicephalus and L. megastoma proposed to be paedomoiphic and peramoiphic, respectively; (ii) studied the role of thyroid hormone (TH) in the regulation of L. intermedius development; (iii) evaluated the effect of TH changes on the definitive morphology, and (iv) evaluated the possible role of TH in diversification of Tana barbs. Skull development was found to be heterochronicaily changed in L. brevicephalus and L. megastoma as compared to L. intermedius; revealed heteroclironies may account for differences in skull proportions distinguishing these barbs, TH was shown to play a major role in the regulation of ontogeny. Changes in TH level cause heterochronies in the development of a skull, axial skeleton, fins and fin girdles, squamation, and dentition. Heteroclironies were shown to influence adult morphology of these structures. These findings support the hypothesis of the involvement of developmental and hormonal factors in the diversification of the Lake Tana large barbs.     

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.     

Evolution and origin of sympatric shallow-water morphotypes of Lake Trout,Salvelinus namaycush,in Canada's Great Bear Lake

Range expansion in north-temperate fishes subsequent to the retreat of the Wisconsinan glaciers has resulted in the rapid colonization of previously unexploited, heterogeneous habitats and, in many situations, secondary contact among conspecific lineages that were once previously isolated. Such ecological opportunity coupled with reduced competition likely promoted morphological and genetic differentiation within and among post-glacial fish populations. Discrete morphological forms existing in sympatry, for example, have now been described in many species, yet few studies have directly assessed the association between morphological and genetic variation. Morphotypes of Lake Trout, Salvelinus namaycush, are found in several large-lake systems including Great Bear Lake (GBL), Northwest Territories, Canada, where several shallow-water forms are known. Here, we assess microsatellite and mitochondrial DNA variation among four morphotypes of Lake Trout from the five distinct arms of GBL, and also from locations outside of this system to evaluate several hypotheses concerning the evolution of morphological variation in this species. Our data indicate that morphotypes of Lake Trout from GBL are genetically differentiated from one another, yet the morphotypes are still genetically more similar to one another compared with populations from outside of this system. Furthermore, our data suggest that Lake Trout colonized GBL following dispersal from a single glacial refugium (the Mississippian) and support an intra-lake model of divergence. Overall, our study provides insights into the origins of morphological and genetic variation in post-glacial populations of fishes and provides benchmarks important for monitoring Lake Trout biodiversity in a region thought to be disproportionately susceptible to impacts from climate change.     

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     

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.     

Development of skeleton elements in juvenile dwarf and small sympatric forms of <Emphasis Type="Italic">Salvelinus alpinus</Emphasis> complex from Lake Davatchan (Transbaikalia)

The development of skeleton elements was studied in prolarvae, larvae, and fry of two morphologically different forms of the Arctic char Salvelinus alpinus complex—small plankton-eating and dwarf (having a seasonal change of plankton and benthic feeding)—that sympatrically inhabit Lake Davatchan (Transbaikalia). According to genetic data, these forms diverged in this lake from a specialized lacustrine ecotype of char and reached reproductive isolation. Comparative analysis revealed similarity in the shape of anlagen and transitive states of cranial bones. In prolarvae and larvae of the dwarf form, the onset of similar morphological states of skeleton elements occurs at a smaller body length than in fish of the small form. Differences in the development of serial skeleton structures (teeth, gill rakers, fin rays, centra, and scales), heterochronies of timing of appearance and rate of differentiation of skeleton elements were found. It is suggested that these differences resulted from the ecological differentiation of the two forms according to spawning grounds that became local habitats of larvae and fry (sublittoral and hypolimnion). The initial divergence could be caused by the presence in the lake of two (autumn and spring-summer) peaks of numbers of food organisms.