Evolutionary history and speciation modes in the cyprinid genus Barbus.

Phylogenetic relationships and evolutionary patterns in the genus Barbus were examined through the analysis of the complete sequences of three mitochondrial genes: ATPases 8 and 6, which overlap slightly, and cytochrome b. This complex genus includes diploid as well as tetraploid and hexaploid species that are distributed throughout the Palaearctic, Ethiopian and Asiatic biogeographical regions. Given that genome duplication is an important evolutionary mechanism in eukaryotes, in the present report we attempt to describe its role in the evolution of the genus Barbus, as well as drawing systematic and phylogenetic conclusions. The phylogenetic results indicated the splitting of the current Barbus genus into five main mitochondrial lineages corresponding to (i) the genus Barbus sensu stricto (tetraploid, which is subdivided into the subgenera Barbus and Luciobarbus), (ii) the hexaploid species, (iii) the Ethiopian tetraploid species, (iv) the African diploid species, and (v) the Asian diploid species. The branching of 'foreign' genera as sister groups of some of these monophyletic assemblages (such as Aulopyge is to Barbus sensu stricto or Varicorhinus is to the hexaploid barbels) demonstrates the polyphyly of the group. Moreover, the relationships between the proposed lineages also show that genome duplication may be considered as a homoplasic character since it must have occurred over at least three independent periods and/or in three independent areas. In relation to the possible saltational evolutionary model for the polyploid species examined here, it was found that, although feasible at the nuclear level, the mitochondrial markers looked at do not appear to have undergone this type of evolution. Rather, they seem to have experienced more or less constant change through time.     

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.     

Molecular phylogeny and biogeography of African diploid barbs, ‘Barbus’, and allies in Africa and Asia (Teleostei: Cypriniformes)

African diploid barbs (‘Barbus’, Clypeobarbus, Barboides, etc.) are a group of small cyprinids with a body size less than 20 cm and widely distributed in drainages across Africa. These species constitute a significant component of African freshwater fish fauna. This study is the first to focus on the molecular systematics and biogeography of African diploid barbs ‘Barbus’ and its African and Asian allies using both mitochondrial and nuclear genes. We test for monophyly of groups, determine interspecific relationships and estimate the time of divergence of 52 species of ‘Barbus’ and allies using two mitochondrial and four nuclear genes. Resulting trees demonstrate that ‘Barbus’ and allies (Systomus, Barboides, Clypeobarbus and African tetraploid barbs) form a strongly supported clade; however, ‘Barbus’ is not resolved as monophyletic. Divergence time analyses identify the separation between Systomus and ‘Barbus’ plus African allies may have occurred around 26 MYA. In addition to the phylogenetic results, these findings highlight the need for more thorough taxonomic and systematic studies on ‘Barbus’ and allies using morphological and additional molecular data and greater taxon sampling, including the type species of the genus Enteromius, ‘Barbus’ potamogalis.     

Phylogenetic position of Mediterranean Astereae and character evolution of daisies (Bellis,Asteraceae) inferred from nrDNA ITS sequences

Phylogenetic analyses of nrITS sequences of Asteraceae revealed that the Bellis group is a natural assemblage comprising all the species of Bellis and Bellium, but not Rhynchospermum. In contrast, we propose to include the genera Bellis, Bellium, and Bellidastrum in the subtribe Bellidinae in the interest of circumscribing natural groups. Our results also suggest an early diversification in the western Mediterranean Basin of two monophyletic lineages, Bellis and Bellium. Three major groups can be distinguished within BELLIS: (1) the B. perennis group, containing five annual and perennial species with three ploidy levels (diploid, octoploid, and decaploid), which are distributed throughout the Mediterranean Basin despite lack of pappus; (2) the Bellis sylvestris group, with five annual and perennial species primarily from the western Mediterranean, in which there are five ploidy levels (diploid, tetraploid, hexaploid, octoploid, and decaploid); and (3) a basal grade consisting of three diploid, perennial species which displays remarkable diversification of morphologies. Striking characteristics, such as an annual life form, polyploidy, and loss of pappus, seem to have occurred in parallel several times and in different geographical areas during the early diversification of Bellis species in the western Mediterranean. Character evolution reconstructions allow us to describe a putative ancestor of the genus Bellis (proto-Bellis).     

Molecular phylogeny of the Southeast Asian freshwater fish family Botiidae (Teleostei: Cobitoidea) and the origin of polyploidy in their evolution

The freshwater fish family Botiidae is represented by seven genera on the Indian subcontinent and in East and Southeast Asia and includes diploid as well as evolutionary tetraploid species. We present a phylogeny of Botiidae including 33 species representing all described genera using the mitochondrial cytochrome b and 12s rRNA genes to reconstruct the phylogenetic relationships among the genera and to estimate the number of polyploidisation events during their evolution. Our results show two major lineages, the subfamilies Leptobotiinae with the genera Leptobotia and Parabotia and Botiinae with the genera Botia, Chromobotia, Sinibotia, Syncrossus, and Yasuhikotakia. Our results suggest that two species that were traditionally placed into the genus Yasuhikotakia form a monophyletic lineage with the species of Sinibotia. A review of the data on the ploidy level of the included species shows all diploid species to belong to Leptobotiinae and all tetraploid species to Botiinae. A single polyploidisation event can therefore be hypothesised to have occurred in the ancestral lineage leading to the Botiinae.     

Association of ploidy and sexual system in Lycium californicum (Solanaceae)

In North American Lycium (Solanaceae), the evolution of gender dimorphism has been proposed as a means of restoring outcrossing after polyploidization causes the loss of self-incompatibility. Previous studies of this process in Lycium focused on comparisons between species that differ in ploidy. We examined intraspecific variation in floral morphology and DNA content in populations of L. californicum to determine correlations between sexual system and cytotype. We also used nuclear ITS and GBSSI sequence data to determine whether diploid and polyploid forms represent the same phylogenetic species, and the phylogeographic relationships among populations and ploidy levels. Within populations, no variation in ploidy was found, although among populations there was a perfect correspondence between sexual system and cytotype. Diploid populations were all hermaphroditic, whereas tetraploid populations were all gender dimorphic. There was no clear geographic pattern to the occurrence of diploid and tetraploid forms. Phylogenetic analysis confirms that L. californicum, regardless of ploidy, forms a monophyletic group within the genus Lycium. Sequences from diploid and polyploid individuals did not form reciprocally monophyletic clades, indicating either multiple gains of polyploidy, ongoing gene flow between cytotypes, or lack of lineage sorting since the evolution of polyploidy. The correspondence between ploidy and sex expression is consistent with the hypothesis that polyploidization triggers the evolution of gender dimorphism in this and other Lycium species.     

Effect of ploidy levels on the activities of Δ1-pyrroline-5-carboxylate synthetase,superoxide dismutase and peroxidase in Cenchrus species grown under water stress

The effects of ploidy levels on the activities of Δ¹-pyrroline-5-carboxylate synthetase (P5CS; EC not assigned), superoxide dismutase (SOD; EC 1.15.1.1) and guaiacol peroxidase (POX; EC 1.11.1.7), as well as malondialdehyde (MDA) and proline contents were studied in two months old plants of Cenchrus species. The Cenchrus species represent three ploidy levels: diploid, tetraploid, hexaploid and two life spans: annual and perennial. Plants were subjected to water stress for 2, 4, 6 and 8 d by withholding water under glasshouse conditions. Although the levels of proline increased with the magnitude of water stress, the P5CS activity did not show a corresponding increase in all species. Peroxidase and superoxide dismutase activities showed an increase or steady state in the early phase of drought and then declined with the further increase in the magnitude of water stress, indicating differing behaviors of species towards drought tolerance. Under drought, diploid Cenchrus species had a higher POX activity, MDA accumulation and lower proline content than tetraploid species. Lower POX and higher P5CS activities and proline contents, however, were observed in hexaploid and tetraploid species. Taken together, our findings suggest that diploid species have a less efficient antioxidant system to scavenge reactive oxygen species than tetra and hexaploid Cenchrus. This may result in a corresponding variability in growth and persistence under natural grasslands. The study also paves the way for investigations on the molecular events associated with drought in Cenchrus species differing in ploidy and life span.     

不同倍性猕猴桃的适生区预测及生态位分化

多倍体与2倍体植物之间的生态位分化是多倍体植物成功建立的重要条件。2倍体、4倍体和6倍体猕猴桃分布在不同的地区,目前尚不明确不同倍性猕猴桃之间是否发生了明显的生态位分化,也不明确影响不同倍性猕猴桃生态位的主要环境因子。本研究通过文献查阅和野外调查收集不同倍性猕猴桃的自然分布点,利用最大熵模型预测不同倍性猕猴桃在当前气候条件下的潜在适生区及影响其分布的主导气候因子,并通过生态位一致性检验评估不同倍性猕猴桃间的生态位差异。结果表明: 不同倍性猕猴桃的潜在适生区存在明显差异,2倍体猕猴桃的高适生区集中在海拔较低的湖南丘陵;4倍体猕猴桃的高适生区大部分与2倍体重叠,但有部分向贵州北部、重庆东部区域偏移;6倍体猕猴桃的高适生区则集中分布在贵州大部、湖南西北部、湖北西南部和陕西南部。6倍体猕猴桃明显向高海拔、高纬度地区偏移,并且有更广的高适生区面积。生态位一致性检验证明,2倍体与4倍体猕猴桃有重叠的生态位,而2倍体与6倍体、4倍体与6倍体猕猴桃之间均发生了明显的生态位分化。最冷月最低温(Bio6)和最干月降雨量(Bio14)是影响不同倍性猕猴桃生态位分化的主要环境因素。多倍体猕猴桃在较低的Bio6和Bio14下能保持较高的存在概率,表明多倍体猕猴桃能占据低温、干旱的极端生态位。     

Studies in the Hordeum murinum L. aggregate: disc electrophoresis of seed proteins

Seeds of the H. murinum aggregate were collected from much of the range of the group and soluble protein extracts were subject to gel-electrophoresis analysis. Diploid, tetraploid and hexaploid plants were readily differentiated. Analysis using a similarity matrix and dendrogram revealed further groups within the ploidy levels and indicated inter-group relationships. Evidence obtained supported karyological results, suggesting that tetraploid and hexaploid plants are allopolyploids, and that one of their putative parents is a diploid known from Turkey and adventive in Australia. Within the tetraploids there is little correspondence between groups detected by either gel-electrophoresis or karyology, and the species H. leporinum (mostly southern) and H. murinum (mostly northern).     

Cytogeography and reproduction of the Paspalum simplex polyploid complex

 Paspalum simplex is a grass distributed throughout the phytogeographic Chaco region in South America from which sexual diploid and apomictic tetraploid races have been reported. We analysed native populations to determine their homogeneity of ploidy level, and the relationship between geographic distribution, ploidy levels, and reproductive systems. The ploidy level was established for 379 plants from 32 wild populations. Tetraploidy and apomixis constitute the most common combination for this species all over the Chaco region. Apomictic hexaploid plants were found associated with 4x populations. Diploids were confined to a small sector of the region. One sexual triploid plant arose from seed harvested in a pure 2x population, and one apomictic 3x plant was found in a mixed 2x-4x population. The results suggest that P. simplex is a core agamic complex characteristic of the Chaco region from which other apomictic polyploid species of the subgenus Anachyris could have evolved. Received July 24, 2002; accepted September 12, 2002 Published online: December 11, 2002     

Ancestry of American polyploid Hordeum species with the I genome inferred from 5S and 18S-25S rDNA

* BACKGROUND AND AIMS: The genus Hordeum exists at three ploidy levels (2x, 4x and 6x) and presents excellent material for investigating the patterns of polyploid evolution in plants. Here the aim was to clarify the ancestry of American polyploid species with the I genome. * METHODS: Chromosomal locations of 5S and 18S-25S ribosomal RNA genes were determined by fluorescence in situ hybridization (FISH). In both polyploid and diploid species, variation in 18S-25S rDNA repeated sequences was analysed by the RFLP technique. * KEY RESULTS: Six American tetraploid species were divided into two types that differed in the number of rDNA sites and RFLP profiles. Four hexaploid species were similar in number and location of both types of rDNA sites, but the RFLP profiles of 18S-25S rDNA revealed one species, H. arizonicum, with a different ancestry. * CONCLUSIONS: Five American perennial tetraploid species appear to be alloploids having the genomes of an Asian diploid H. roshevitzii and an American diploid species. The North American annual tetraploid H. depressum is probably a segmental alloploid combining the two closely related genomes of American diploid species. A hexaploid species, H. arizonicum, involves a diploid species, H. pusillum, in its ancestry; both species share the annual growth habit and are distributed in North America. Polymorphisms of rDNA sites detected by FISH and RFLP analyses provide useful information to infer the phylogenetic relationships of I-genome Hordeum species because of their highly conserved nature during polyploid evolution.     

Ecological differentiation,lack of hybrids involving diploids,and asymmetric gene flow between polyploids in narrow contact zones of Senecio carniolicus (syn. Jacobaea carniolica,Asteraceae)

Areas of immediate contact of different cytotypes offer a unique opportunity to study evolutionary dynamics within heteroploid species and to assess isolation mechanisms governing coexistence of cytotypes of different ploidy. The degree of reproductive isolation of cytotypes, that is, the frequency of heteroploid crosses and subsequent formation of viable and (partly) fertile hybrids, plays a crucial role for the long‐term integrity of lineages in contact zones. Here, we assessed fine‐scale distribution, spatial clustering, and ecological niches as well as patterns of gene flow in parental and hybrid cytotypes in zones of immediate contact of di‐, tetra‐, and hexaploid Senecio carniolicus (Asteraceae) in the Eastern Alps. Cytotypes were spatially separated also at the investigated microscale; the strongest spatial separation was observed for the fully interfertile tetra‐ and hexaploids. The three main cytotypes showed highly significant niche differences, which were, however, weaker than across their entire distribution ranges in the Eastern Alps. Individuals with intermediate ploidy levels were found neither in the diploid/tetraploid nor in the diploid/hexaploid contact zones indicating strong reproductive barriers. In contrast, pentaploid individuals were frequent in the tetraploid/hexaploid contact zone, albeit limited to a narrow strip in the immediate contact zone of their parental cytotypes. AFLP fingerprinting data revealed introgressive gene flow mediated by pentaploid hybrids from tetra‐ to hexaploid individuals, but not vice versa. The ecological niche of pentaploids differed significantly from that of tetraploids but not from hexaploids.     

Pollen and stomata morphometrics and polyploidy in Eriotheca (Malvaceae‐Bombacoideae)

Approximately 70% of the angiosperm species are polyploid, an important phenomenon in the evolution of those plants. But ploidy estimates have often been hindered because of the small size and large number of chromosomes in many tropical groups. Since polyploidy affects cell size, morphometric analyses of pollen grains and stomata have been used to infer ploidy level. Polyploidy is present in many species of the Cerrado, the Neotropical savanna region in Central Brazil, and has been linked to apomixis in some taxa. Eriotheca gracilipes and Eriotheca pubescens are common tree species in this region, and present cytotypes that form reproductive mosaics. Hexaploid individuals (2n = 6x = 276) are polyembryonic and apomictic, while tetraploid and diploid individuals (2n = 2x = 92, 2n = 4x = 184) are sexual and monoembryonic. We tested whether morphometric analysis can be used to estimate ploidy levels in E. gracilipes and E. pubescens individuals. Pollen material from diploid and hexaploid individuals of E. gracilipes, and tetraploid and hexaploid individuals of E. pubescens, were fixed in 50% FAA, and expanded leaves were dried in silica gel. Pollen grains and stomata of at least five individuals from each population were measured. The results demonstrate that all measures were significantly different among cytotypes. Individuals with higher levels of ploidy (hexaploid) all presented measurements that were higher than those with lower levels (diploid and tetraploid). There was no overlap between ploidy levels in each species at 95% confidence interval. Thus, the size of the pollen grains and stomata are effective parameters for analysis of ploidy levels in E. gracilipes and E. pubescens.     

Hybridization in the genera Vulpia and Festuca (Poaceae): meiotic behaviour of artificial hybrids

The course of meiosis, including an analysis of chromosome configurations, is described for five diploid × diploid Vulpia crosses, five tetraploid × diploid Vulpia crosses, one hexaploid × diploid Festuca × Vulpia cross, one tetraploid × hexaploid Vulpia × Festuca cross, and one hexaploid × hexaploid Vulpia × Festuca cross. In most cases there was 97.5% or more pollen sterility, but two heptaploid plants obtained (presumably by non-reduction) from a hexaploid × diploid cross had about 60% stainable pollen. In the diploid hybrids pairing was quite extensive, and in V. ligustica × V. geniculata it was more or less as in the parent species (mode 7 bivalents, with regular separation). In the triploid hybrids the modal situation was 7 bivalents + 7 univalents, but evidence concerning the genomes which were pairing was equivocal. Evidence from the crosses at higher ploidy levels shows that both homogenetic and heterogenetic pairing does occur, although the relative amounts are uncertain. The results in general support the current classsification of Vulpia , except that they suggest the removal of V. alopecuros from section Loretia.     

Polyploidy in Cupressaceae: Discovery of a new naturally occurring tetraploid,Xanthocyparis vietnamensis

While polyploidy (whole-genome multiplication) is generally considered rare in extant gymnosperms (with the exception of Ephedra, Ephedraceae), the occurrence of sporadic polyploid individuals belonging to various genera in the conifer family Cupressaceae has been reported in the literature. In addition, recent studies have revealed that polyploidy is not uncommon in the genus Juniperus (Cupressaceae), with tetraploid and hexaploid individuals reported in individuals collected from wild populations. Given these findings, we undertook a comprehensive screening of ploidy levels in 32 species belonging to the four genera that are phylogenetically closest to Juniperus (i.e.,Callitropsis, Hesperocyparis, Xanthocyparis, and Cupressus), referred to as the CaHXCu complex. In addition, we also determined the ploidy level of two accessions in the poorly studied tetraploid, Fitzroya cupressoides. Using flow cytometry together with published chromosome counts to assign ploidy levels, we show that all species of the CaHXCu complex are diploid except Xanthocyparis vietnamensis, which is tetraploid, with a genome size of 44.60 pg/2 C. This study opens up new opportunities for studying the impact and consequences of polyploidy on the evolution and adaptation of species in Cupressaceae.     

Polyploidy,phylogeography and Pleistocene refugia of the rockfern Asplenium ceterach: evidence from chloroplast DNA

Chloroplast DNA sequences were obtained from 331 Asplenium ceterach plants representing 143 populations from throughout the range of the complex in Europe, plus outlying sites in North Africa and the near East. We identified nine distinct haplotypes from a 900 bp fragment of trnL-trnF gene. Tetraploid populations were encountered throughout Europe and further afield, whereas diploid populations were scarcer and predominated in the Pannonian-Balkan region. Hexaploids were encountered only in southern Mediterranean populations. Four haplotypes were found among diploid populations of the Pannonian-Balkans indicating that this region formed a northern Pleistocene refugium. A separate polyploid complex centred on Greece, comprises diploid, tetraploid and hexaploid populations with two endemic haplotypes and suggests long-term persistence of populations in the southern Mediterranean. Three chloroplast DNA (cpDNA) haplotypes were common among tetraploids in Spain and Italy, with diversity reducing northwards suggesting expansion from the south after the Pleistocene. Our cpDNA and ploidy data indicate at least six independent origins of polyploids.     

Nuclear and cytoplasmic genome relationships in the genus Avena: Analysis by isoelectric focusing of ribulose biphosphate carboxylase subunits

Comparisons of the isoelectric points of small and large subunits of ribulose biphosphate carboxylase extracted from a number of diploid, tetraploid, and hexaploid Avena species have been used to obtain information on the nuclear and cytoplasmic genome relationships within the genus. All species tested had small subunits with similar isoelectric points, so their analysis provided no information of taxonomic value. Three types of large subunits could be distinguished by this method, and the distribution of each among the available species provides strong evidence against the involvement of a C genome diploid (such as A. ventricosa) as the maternal parent in the formation of either tetraploid or hexaploid species. One type of large subunit was confined to the perennial tetraploid, A. macrostachya, and its position in the genus and possible origin are discussed. The value of this approach in studying genome relationships within the genus Avena and related genera is assessed.     

Detecting Nucleotide Additivity from Direct Sequences is a SNAP: An Example from Sidalcea (Malvaceae)

Abstract: Superimposed nucleotide additivity patterns (SNAPs) were detected from direct sequences of the nuclear ribosomal DNA internal transcribed spacers in a complex of perennial Sidalcea species (Malvaceae) from the Pacific Northwest of the United States. Although only 2.8 % sequence variation exists among the eight ITS accessions, parsimony analysis identified two distinct lineages within this complex consistent with known ploidy levels. Six SNAPs were identified in a known tetraploid S. virgata, suggesting allopolyploid origins from diploid S. virgata and one of two hexaploid Sidalcea species. A dosage effect detected at all six SNAP sites is consistent with the unequal sized parental genomes of allopolyploid S. virgata.     

Assessment of ploidy level on stress tolerance of <Emphasis Type="Italic">Cenchrus</Emphasis> species based on leaf photosynthetic characteristics

Many species of the genus Cenchrus, with different ploidy are important components of world grasslands. In the present investigation, influence of ploidy on leaf water potential (Ψ_leaf) and photosynthetic characteristics under water-stress condition was studied in 2-month-old plants of eight Cenchrus species representing three ploidy and two life spans. Stress was imposed for 2, 4, 6, and 8 days by withholding watering. Decrease in water potential, chlorophyll content, photosynthetic rate (P _N), stomatal conductance for CO₂ (g _s), and carboxylation efficiency (P _N/C _i) occurred in all species. Nevertheless, perennial and diploid C. setigerus maintained the highest P _N/C _i at maximum stress indicating its higher assimilation potential. Photosynthetic water use efficiency (P _N/E) in general decreased with increase of water stress; however, at low stress, reverse trend was observed in diploid C. prieurri, C. setigerus, and tetraploid C. glaucus. Results indicate that relative reduction in photosynthetic characteristics was more in annual diploid than perennial diploid and tetraploid. Stress tolerance in terms of plant height, rolling and wilting of leaves also indicated better adaptability of tetra and hexaploid species over diploid. Moreover, recovery of different physiological traits was more pronounced in perennial tetraploid and hexaploid over annual diploid, thus making them suited more to drought conditions. Analysis of variance results showed direct correlation (r = 0.675) of ploidy with gas exchange parameters indicating better impact of this on physiological performance of different species of Cenchrus under water stress. This is the first report where influence of ploidy levels on photosynthetic characteristics and overall responses to moisture stress is studied in a tropical grass species.     

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.