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     

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.     

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.     

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.     

The role of the thyroid gland hormone in ontogenesis and morphological diversification of Barbus intermedius sensu of Lake Tana in Ethiopia

The role of thyroid gland hormone in the ontogenesis of the Large African Barb Barbus intermedius sensu Banister, 1973 (Teleostei; Cyprinidae)--the supposed ancestral species which produced the species flock of the large African Barbs of the Lake Tana (Ethiopia)--has been studied. It has been shown that the thyroid hormone influences the period of many morphological processes and a change in its level causes heterochrony, reflecting on the definitive morphology of fish. Thus, it can be assumed that even a slight change in activity of the thyroid axis in the process of ontogenesis can be the cause of wide variability of the morphological features of B. intermedius and is at the basis for the fast diversification of the species flock of Big African Barbs of Lake Tana.     

Morphological diversity and age dependent transformations in progeny of the large barbs (Barbus intermedius complex sensu Banister) of several morphotypes from Lake Tana (Ethiopia). Results of a long-time experiment

Results of a long-time (2005?C2011) experiment in crossing and rearing the large African barbs from Lake Tana (Ethiopia) are presented. One may conclude that progeny from homonomic crossings of large-mouthed barbs acquire diagnostic traits of their parental morphotype at different age. Some males originated from different crossings reached sexual maturity before acquiring diagnostic traits of a certain morphotype. Siblings from both homonomic and heteronomic crossings living in the same conditions considerably differed both in external and in skull characters. Differences both in external and skull characters between some siblings originated from a homonomic crossing that lived in a pond and those that lived in aquaria were equivalent to the differences between moiphotypes.     

Evolution of MHC class I genes in the European badger (Meles meles)

The major histocompatibility complex (MHC) plays a central role in the adaptive immune system and provides a good model with which to understand the evolutionary processes underlying functional genes. Trans-species polymorphism and orthology are both commonly found in MHC genes; however, mammalian MHC class I genes tend to cluster by species. Concerted evolution has the potential to homogenize different loci, whereas birth-and-death evolution can lead to the loss of orthologs; both processes result in monophyletic groups within species. Studies investigating the evolution of MHC class I genes have been biased toward a few particular taxa and model species. We present the first study of MHC class I genes in a species from the superfamily Musteloidea. The European badger (Meles meles) exhibits moderate variation in MHC class I sequences when compared to other carnivores. We identified seven putatively functional sequences and nine pseudogenes from genomic (gDNA) and complementary (cDNA) DNA, signifying at least two functional class I loci. We found evidence for separate evolutionary histories of the α1 and α2/α3 domains. In the α1 domain, several sequences from different species were more closely related to each other than to sequences from the same species, resembling orthology or trans-species polymorphism. Balancing selection and probable recombination maintain genetic diversity in the α1 domain, evidenced by the detection of positive selection and a recombination event. By comparison, two recombination breakpoints indicate that the α2/α3 domains have most likely undergone concerted evolution, where recombination has homogenized the α2/α3 domains between genes, leading to species-specific clusters of sequences. Our findings highlight the importance of analyzing MHC domains separately.     

The class II genes of the rat MHC

Genes that encode class II Ag from the MHC of the rat, the RT1 region, have been isolated as a series of cosmid clones. The cosmids define two clusters, each of which contains three identifiable sequences; one homologous to alpha-chain and two to beta-chain genes. Both the serologically identified rat class II Ag have been expressed in mouse L cell fibroblasts after the introduction of each alpha-chain gene along with a beta-chain gene from the same cluster. There are substantial homologies to the I region of the mouse H-2 complex in the presence, location, orientation, and expression of the six identified sequences from the rat RT1, supporting the view that the overall organization of the two gene complexes has remained conserved since the species separated.     

Comprehensive analysis of medaka major histocompatibility complex (MHC) class II genes: Implications for evolution in teleosts

The major histocompatibility complex (MHC) class II molecules play central roles in adaptive immunity by regulating immune response via the activation of CD4 T cells. The full complement of the MHC class II genes has been elucidated only in mammalian species to date. To understand the evolution of these genes, we performed their first comprehensive analysis in nonmammalian species using a teleost, medaka (Oryzias latipes). Based on a database search, cDNA cloning, and genomic PCR, medaka was shown to possess five pairs of expressed class II genes, comprising one IIA and one IIB gene. Each pair was located on a different chromosome and was not linked to the class I genes. Only one pair showed a high degree of polymorphism and was considered to be classical class II genes, whereas the other four pairs were nonclassical. Phylogenetic analysis of all medaka class II genes and most reported teleost class II genes revealed that the IIA and IIB genes formed separate clades, each containing three well-corresponding lineages. One lineage contained three medaka genes and all known classical class II genes of Ostariophysi and Euteleostei and was presumed to be an original lineage of the teleost MHC class II genes. The other two lineages contained one nonclassical medaka gene each and some Euteleostei genes. These results indicate that multiple lineages of the teleost MHC class II genes have been conserved for hundreds of millions of years and that the tightly linked IIA and IIB genes have undergone concerted evolution.     

Phylogeography of the barbel (Barbus barbus) assessed by mitochondrial DNA variation

Using the phylogeographic framework, we assessed the DNA sequence variation at the mitochondrial cytochrome b gene across the distribution range of the barbel Barbus barbus, a widely distributed European cyprinid. Reciprocal monophyly of non-Mediterranean European and Balkan/Anatolian populations is taken as evidence for a long-term barrier to gene flow, and interpreted as a consequence of survival of the species in two separate refugia during several later glacial cycles. Lack of profound genealogical divergence across Europe from western France to the northwestern Black Sea basin is consistent with recent colonization of this area from a single glacial refuge, which was probably located in the Danube River basin. This may have occurred in two steps: into the Western European river basins during the last interglacial, and throughout the Central European river basins after the last glacial. The populations from the Balkans and Anatolia apparently did not contribute mitochondrial DNA to the post-Pleistocene colonization of non-Mediterranean Europe. Lack of detectable variation within the Balkans/Anatolia is attributed mainly to recent expansion throughout these regions, facilitated by the freshwater conditions and seashore regression in the Black Sea during the Late Pleistocene and Early Holocene.     

Independent evolution of functional MHC class II DRB genes in New World bat species

Genes of the major histocompatibility complex (MHC) play a pivotal role in the vertebrate immune system and are attractive markers for functional, fitness-related, genetic variation. Although bats (Chiroptera) represent the second largest mammalian order and are prone to various emerging infectious diseases, little is known about MHC evolution in bats. In the present study, we examined expressed MHC class II DRB sequences (exons 1 to 4) of New World bat species, Saccopteryx bilineata, Carollia perspicillata, Noctilio albiventris and Noctilio leporinus (only exon 2). We found a wide range of copy number variation of DRB loci with one locus detected in the genus Noctilio and up to ten functional loci observed in S. bilineata. Sequence variation between alleles of the same taxa was high with evidence for positive selection. We found statistical support for recombination or gene conversion events among sequences within the same but not between bat species. Phylogenetic relationships among DRB alleles provided strong evidence for independent evolution of the functional MHC class II DRB genes in the three investigated species, either by recent gene duplication, or homogenization of duplicated loci by frequent gene conversion events. Phylogenetic analysis of all available chiropteran DRB exon 2 sequences confirmed their monophyletic origin within families, but revealed a possible trans-species mode of evolution pattern in congeneric bat species, e.g. within the genera Noctilio and Myotis. This is the first study investigating phylogenetic relationships of MHC genes within bats and therefore contributes to a better understanding of MHC evolution in one of the most dominant mammalian order.     

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.     

Evolution in isolation: the Gyraulus species flock from Miocene Lake Steinheim revisited

The Miocene Steinheim Basin in SW Germany is an ancient (long-lived) palaeo-lake that has existed over some hundreds of thousands of years. It is an iconic fossil site, because the historically oldest phylogenetic tree of extinct organisms was based on specimens described from this locality. Today the basin contains 30–40 m thickness of lake sediments with planorbid snails of the genus Gyraulus occurring in rock-forming quantities. The shells are morphologically highly disparate with forms ranging from the tiny, planispiral founder species Gyraulus kleini, to fragile corkscrew-like uncoiled forms and to large trochiform morphs with thick shells. In total, this presumably monophyletic species flock contains 17 species distributed in time and space, all of which are endemic, except for the founder species. Up to nine of them occur in a single sedimentary level and are inferred to have lived together. Such an extreme rate of endemism makes fossil Lake Steinheim special among extant and fossil lakes. This review article summarises and discusses the species concept(s), indications for endemism, speciation processes, the phylogenetic concept(s) and factors controlling evolution. It also provides directions for future research.     

Isolation and characterization of major histocompatibility complex (MHC) class II B genes in the Barn owl (Aves: Tyto alba)

We isolated major histocompatibility complex class II B (MHCIIB) genes in the Barn owl (Tyto alba). A PCR-based approach combined with primer walking on genomic and complementary DNA as well as Southern blot analyses revealed the presence of two MHCIIB genes, both being expressed in spleen, liver, and blood. Characteristic structural features of MHCIIB genes as well as their expression and high non-synonymous substitution rates in the region involved in antigen binding suggest that both genes are functional. MHC organization in the Barn owl is simple compared to passerine species that show multiple duplications, and resembles the minimal essential MHC of chicken.