Reproductive strategies of diploid and polyploid populations of arcticDraba (Brassicaceae)

132 cultivated populations (2x–16x) of 15 arctic-alpine species ofDraba were investigated to clarify a possible relationship between reproductive strategies and polyploid evolution in the genus. The populations were exclusively sexual and produced viable seed after spontaneous self-pollination, but showed large variation both in traits promoting cross-pollination and in autogamous fruit and seed set. Traits promoting cross-pollination, e.g., floral display, protogyny, and delayed selfing, were positively correlated, and these traits were negatively correlated with autogamous fruit and seed set. All diploid and many polyploid populations had high autogamous seed set and small, unscented, non-protogynous, and rapidly selfing flowers. In contrast, all populations with low autogamous seed set and large, scented, and strongly protogynous flowers with distinctly delayed selfing were polyploid. These results are consistent with those previously obtained from enzyme electrophoresis, suggesting that the genetically depauperate diploids are extreme inbreeders and that the highly fixed-heterozygous polyploids vary from extreme inbreeders to mixed maters. The reproductive data lend additional support to the hypothesis that allopolyploidy in arcticDraba serves as an escape from genetic depauperation caused by uniparental inbreeding at the diploid level.     

Cytotype diversity and genome size variation in eastern Asian polyploid Cardamine (Brassicaceae) species

Background and Aims

Intraspecific ploidy-level variation is an important aspect of a species'' genetic make-up, which may lend insight into its evolutionary history and future potential. The present study explores this phenomenon in a group of eastern Asian Cardamine species.

Methods

Plant material was sampled from 59 localities in Japan and Korea, which were used in karyological (chromosome counting) and flow cytometric analyses. The absolute nuclear DNA content (in pg) was measured using propidium iodide and the relative nuclear DNA content (in arbitrary units) was measured using 4,6-diamidino-2-phenylindole fluorochrome.

Key Results

Substantial cytotype diversity was found, with strikingly different distribution patterns between the species. Two cytotypes were found in C. torrentis sensu lato (4x and 8x, in C. valida and C. torrentis sensu stricto, respectively), which displays a north–south geographical pattern in Japan. Hypotheses regarding their origin and colonization history in the Japanese archipelago are discussed. In Korean C. amaraeiformis, only tetraploids were found, and these populations may in fact belong to C. valida. C. yezoensis was found to harbour as many as six cytotypes in Japan, ranging from hexa- to dodecaploids. Ploidy levels do not show any obvious geographical pattern; populations with mixed ploidy levels, containing two to four cytotypes, are frequently observed throughout the range. C. schinziana, an endemic of Hokkaido, has hexa- and octoploid populations. Previous chromosome records are also revised, showing that they are largely based on misidentified material or misinterpreted names.

Conclusions

Sampling of multiple populations and utilization of the efficient flow cytometric approach allowed the detection of large-scale variation in ploidy levels and genome size variation attributable to aneuploidy. These data will be essential in further phylogenetic and evolutionary studies.     

Enzyme analysis of genetic variation and relationships in diploid and polyploid taxa ofGalium (Rubiaceae)

Allozyme variation at 11 loci (with 37 alleles) was studied electrophoretically in seven outbreeding, closely related diploid and tetraploid taxa, seven from sect.Leptogalium and two from sect.Leiogalium. Whereas the sections are clearly distinct by several different alleles, aggregates, species and subspecies differ only in the frequency or presence/absence of common alleles. The resulting dendrogram suggests phylogenetic relationships and is supported by other multidisciplinary evidence. Tetraploids have originated independently in several groups, and there is evidence for tetrasomic inheritance and thus for autopolyploidy in spite of normal meiotic bivalent pairing and partly suspected hybrid origin. Tetraploids differ from related diploids only little in number of alleles and expected heterozygosity within populations, but clearly exhibit higher numbers of genotypes. This often corresponds to their greater morphological variability, increased adaptive flexibility, and better colonizing capacity compared to related diploids.     

Evolutionary history of the polyploid complex of Cardamine amara (Brassicaceae): isozyme evidence

 In samples from 56 populations of Cardamine amara, representing four diploid subspecies (subspp. amara, opicii, balcanica, and pyrenaea) and two tetraploid subspecies (subspp. austriaca and olotensis) from different parts of the European distribution area, four enzyme systems with 23 alleles were studied. These data, together with previous morphological and karyological data, suggest that the distribution and variation pattern within the species was strongly influenced by the last glacial period and postglacial migrations. Cardamine amara subsp. pyrenaea is monomorphic for a unique allele, and subsp. balcanica has a unique allele, too which, however, is not fixed in all populations of the taxon. Both taxa seem to be relic ones, although otherwise subsp. balcanica in respect of allelic spectrum much resembles subsp. amara. The other two diploid subspecies, subsp. amara and subsp. opicii, are not characterised by presence of unique alleles but differ in allele frequencies. The two tetraploid subspecies have different evolutionary histories. C. amara subsp. austriaca seems to be an autopolyploid derivative of subsp. amara which colonised open space offered by retreating glaciers in the Eastern Alps. C. amara subsp. olotensis from the Iberian Peninsula represents most probably a polyploid of preglacial time. Received June 22, 2001; accepted May 17, 2002 Published online: September 13, 2002     

Phylogenetic analysis of snow sheep (Ovis nivicola) and closely related taxa

Based on mitochondrial cytochrome b gene sequence analysis, the history of true sheep (Ovis) began approximately 3.12 million years ago (MYA). The evolution of Ovis resulted in three generally accepted genetic groups: Argaliforms, Moufloniforms, and Pachyceriforms. The Pachyceriforms of the subgenus Pachyceros comprise the thin-horn sheep Ovis nivicola (snow sheep), Ovis dalli (Dall and Stone sheep), and Ovis canadensis (Rocky Mountain and desert bighorn). North America wild sheep (O. canadensis and O. dalli) evolved separately from Eurasian wild sheep and diverged from each other about 1.41 MYA. Ancestral stock that gave rise to snow sheep, Moufloniforms, and Argaliforms occurred 2.3 MYA, which then gave rise to two different extant lines of snow sheep that diverged from each other about 1.96 MYA. The more recent nivicola line is genetically closer to the North American wild sheep and may represent a close association during the refugium when Alaska and Siberia were connected by the Bering land bridge. The earlier period of evolution of the Pachyceriforms suggests they may have first evolved in Eurasia, the oldest ancestor then giving rise to North American wild sheep, and that a canadensis-like ancestor most likely gave rise to nivicola. Cytogenetic analysis further validates that the standard diploid number for modern nivicola is 52.     

Cardamine guatemalensis sp. nov. (Brassicaceae) from Guatemala

Cardamine guatemalensis Al‐Shehbaz is described from Zacapa, Guatemala. Its features such as the perennial, scapose, rhizomatous habit and simple leaves are very rare among North American Brassicaceae. The distinguishing characters from other species of Cardamine are discussed.     

Cardamine apennina: a new endemic diploid species of the C. pratensis group (Brassicaceae) from Italy

Italian representatives of the Cardamine pratensis group were investigated using morphometric, karyological, and molecular (AFLP-fingerprinting) analyses. Focus was on resolving the taxonomic and evolutionary position of C. granulosa from Piemonte (NW Italy) and of populations from central Italy, previously included in C. granulosa or C. pratensis s. str. Results show that C. granulosa is a morphologically and genetically well defined diploid species, but is extremely rare and restricted to a small area in Piemonte. Central Italian populations differ from both C. granulosa and C. pratensis s. str., and, although the morphological differentiation is not strongly pronounced, they show marked molecular divergence, suggesting recognition as a new species, Cardamine apennina. Because of their restricted distribution and diploid chromosomal level, C. apennina and C. granulosa may represent basal and quite isolated lineages, whereas reticulation on diploid and polyploid level has affected remaining lineages of the C. pratensis group. Both Italian endemics are endangered due to rarity and habitat loss. A key for identification of the Italian taxa of the C. pratensis group is also provided.     

Cardamine calliphaea sp. nov. (Brassicaceae) from southwestern Greece

Cardamine calliphaea Kit Tan, G. Vold & Giannopoulos sp. nov. (Brassicaceae) is illustrated and described as a new species endemic to Greece. It occurs in the prefectures of Ilia in western Peloponnese and Etolias‐Akarnanias in western Sterea Ellas and bears some resemblance to C. graeca, differing by its dense greyish–white indumentum and by the absence of leaf auricles. Affinities lie with C. glauca and C. plumieri from which it differs conspicuously, among other characters, by its imparipinnate leaves with the terminal leaflet smaller or equal in size to the lateral pairs.     

Analysis of nrDNA polymorphism in closely related diploid sexual, tetraploid sexual and polyploid agamospermous species

Nuclear sequences of ITS1-5.8S-ITS2 region of rDNA may be an important source of phylogenetically informative data provided that nrDNA is cloned and the character of sequence variation of clones is properly analyzed. nrDNA of selected Taraxacum sections was studied to show sequence variation differences among diploid sexual, tetraploid sexual and polyploid agamospermous species. We examined nucleotide characteristics, substitution pattern, secondary structure, and the phylogenetic utility of ITS1-5.8S-ITS2 from 301 clones of 32 species representing 11 sections. The most divergent sequences of ITS1&2 differed by 17.1% and in 5.8S only by 3.7%. The ITS1-5.8S-ITS2 characteristics, integrity and also stability of secondary structures confirmed that pseudogenes are not responsible for the above variation. The within-individual polymorphism of clones implies that the concerted evolution of ITS cistron of agamospermous polyploid Taraxacum is remarkably suppressed. Sequences of ITS clones proved to be a useful tool for mapping pathways of complex reticulation (polyploid hybridity) in agamospermous Taraxacum.     

Hybridization between two polyploid Cardamine (Brassicaceae) species in North-western Spain: discordance between morphological and genetic variation patterns

BACKGROUND AND AIMS: Hybridization is an important evolutionary phenomenon, and therefore a detailed understanding of the dynamics of interspecific gene flow and resulting morphological and genetic patterns is of widespread interest. Here hybridization between the polyploids Cardamine pratensis and C. raphanifolia at four localities is explored. Using different types of data, the aim is to provide simultaneous and direct comparisons between genotype and phenotype variation patterns in the studied hybrid populations. METHODS: Evidence of hybridization has been gathered from morphology, molecular markers (amplified fragment length polymorphism and chloroplast DNA sequences), pollen viability, karyology and nuclear DNA content. KEY RESULTS: All data support extensive gene flow occurring in the hybrid populations. A wide range of morphological and genetic variation is observed, which includes both parental and intermediate types. Unbalanced pollen fertility and several ploidy levels are recorded. CONCLUSIONS: Incongruence reported between genotype and phenotype suggests that parental phenotypes are affected by introgression, and intermediate hybrid phenotypes can be genetically closer to one of the parents. Thus, it is evident that morphology, when used alone, can be misleading for interpreting hybridization, and critical evaluation of other data is needed.     

Cytological studies on diploid and polyploid taxa of the genus Pennisetum Rich

The cytology of thirteen taxa and two hybrids in the genus Pennisetum indicated the distribution of the taxa among the four basic chromosome numbers 5, 7, 8 and 9. The diploid nature of P. ramosum and P. typhoides and the genomic allotetraploid status of P. purpureum was further confirmed. P. massaicum (2n=32), P. orientale (2n=36) and P. subangustum (2n=36) suggested probable autotetraploid nature and the three hexaploids (2n=54) investigated (P. polystachyon, P. longistylis and P. squamulatum) revealed allohexaploid constitution. The natural triploid, P. ruppellii (2n=27) and pentaploid P. villosum (2n=45) were found to be apomicts and they were allotriploid and allopentaploid respectively. The tetraploid-hexaploid complex of P. pedicellatum showed them to be cytotypes only. The cytogenetical behaviour of the hybrid, P. typhoides x P. purpureum with 2n=21 and the trispecies hybrid (P. typhoides x P. purpureum) x P. squamulatum with 2n=48 brought out the homology within the genomes of x=7 and x=9 and also between the genomes with x=7 and x=9. The significance of the inter- and intragenomic chromosome pairing had been brought out from the interspecific hybrids and the natural allotriploid and allopentaploid species having one genome in the haploid condition.The morphological sections of this genus did not correspond with the cytological groups. A high degree of evolutionary specialization was evident in species of the section Gymnothrix. A complete series of polyploids and high degree of heterogeneity from the morphological point of view was brought out in species with x=9.     

Detailed alignment of saccharum and sorghum chromosomes: comparative organization of closely related diploid and polyploid genomes.

The complex polyploid genomes of three Saccharum species have been aligned with the compact diploid genome of Sorghum (2n = 2x = 20). A set of 428 DNA probes from different Poaceae (grasses) detected 2460 loci in F1 progeny of the crosses Saccharum officinarum Green German x S. spontaneum IND 81-146, and S. spontaneum PIN 84-1 x S. officinarum Muntok Java. Thirty-one DNA probes detected 226 loci in S. officinarum LA Purple x S. robustum Molokai 5829. Genetic maps of the six Saccharum genotypes, including up to 72 linkage groups, were assembled into "homologous groups" based on parallel arrangements of duplicated loci. About 84% of the loci mapped by 242 common probes were homologous between Saccharum and Sorghum. Only one interchromosomal and two intrachromosomal rearrangements differentiated both S. officinarum and S. spontaneum from Sorghum, but 11 additional cases of chromosome structural polymorphism were found within Saccharum. Diploidization was advanced in S. robustum, incipient in S. officinarum, and absent in S. spontaneum, consistent with biogeographic data suggesting that S. robustum is the ancestor of S. officinarum, but raising new questions about the antiquity of S. spontaneum. The densely mapped Sorghum genome will be a valuable tool in ongoing molecular analysis of the complex Saccharum genome.     

A new species of Hyphoderma (Meruliaceae, Polyporales) and its discrimination from closely related taxa

Thirty-five corticioid collections from the Canary Islands and Azores Archipelago were examined morphologically and subjected to molecular phylogenetic analysis. These specimens, almost all collected on endemic and/or xerophilic vegetation, were similar in morphological and ecological characteristics to Hypochnicium prosopidis from the Sonoran Desert (Arizona, USA) and Hyphoderma amoenum. Thirty-seven new ITS nrDNA sequences from these specimens, including the nomenclatural type of the above-mentioned species, were obtained and aligned with homologous sequences from GenBank. These collections were distributed in two strongly supported monophyletic clades. However, similar patterns of morphological variability shared by specimens included in both clades and their differences with related species suggest that they should be described as a single new species. Therefore Hyphoderma macaronesicum is proposed. Studies will be required to test, in a more robust multilocus genealogical framework, whether these populations constitute two cryptic species or whether they are the same taxon. The position of Hypochnicium prosopidis in the resolved tree and its morphological characters suggest that it should be included in Hyphoderma and the new combination Hyphoderma prosopidis is proposed.     

Comparative analysis of QTLs affecting plant height and flowering among closely-related diploid and polyploid genomes.

Quantitative trait loci (QTLs) affecting plant height and flowering were studied in the two Saccharum species from which modern sugarcane cultivars are derived. Two segregating populations derived from interspecific crosses between Saccharum officinarum and Saccharum spontaneum were genotyped with 735 DNA markers. Among the 65 significant associations found between these two traits and DNA markers, 35 of the loci were linked to sugarcane genetic maps and 30 were unlinked DNA markers. Twenty-one of the 35 mapped QTLs were clustered in eight genomic regions of six sugarcane homologous groups. Some of these could be divergent alleles at homologous loci, making the actual number of genes implicated in these traits much less than 35. Four QTL clusters controlling plant height in sugarcane corresponded closely to four of the six plant-height QTLs previously mapped in sorghum. One QTL controlling flowering in sugarcane corresponded to one of three flowering QTLs mapped in sorghum. The correspondence in locations of QTLs affecting plant height and flowering in sugarcane and sorghum reinforce the notion that the simple sorghum genome is a valuable "template" for molecular dissection of the much more complex sugarcane genome.     

Comparative analysis of the mitochondrial genomes of oriental spittlebug trible Cosmoscartini: insights into the relationships among closely related taxa

Background

Cosmoscartini (Hemiptera: Cercopoidea: Cercopidae) is a large and brightly colored Old World tropical tribe, currently containing over 310 phytophagous species (including some economically important pests of eucalyptus in China) in approximately 17 genera. However, very limited information of Cosmoscartini is available except for some scattered taxonomic studies. Even less is known about its phylogenetic relationship, especially among closely related genera or species. In this study, the detailed comparative genomic and phylogenetic analyses were performed on nine newly sequenced mitochondrial genomes (mitogenomes) of Cosmoscartini, with the purpose of exploring the taxonomic status of the previously defined genus Okiscarta and some closely related species within the genus Cosmoscarta.

Results

Mitogenomes of Cosmoscartini display similar genomic characters in terms of gene arrangement, nucleotide composition, codon usage and overlapping regions. However, there are also many differences in intergenic spacers, mismatches of tRNAs, and the control region. Additionally, the secondary structures of rRNAs within Cercopidae are inferred for the first time.Based on comparative genomic (especially for the substitution pattern of tRNA secondary structure) and phylogenetic analyses, the representative species of Okiscarta uchidae possesses similar structures with other Cosmoscarta species and is placed consistently in Cosmoscarta. Although Cosmoscarta bimacula is difficult to be distinguished from Cosmoscarta bispecularis by traditional morphological methods, evidence from mitogenomes highly support the relationships of (C. bimacula?+?Cosmoscarta rubroscutellata)?+?(C. bispecularis?+?Cosmoscarta sp.).

Conclusions

This study presents mitogenomes of nine Cosmoscartini species and represents the first detailed comparative genomic and phylogenetic analyses within Cercopidae. It is indicated that knowledge of mitogenomes can be effectively used to resolve phylogenetic relationships at low taxonomic levels. Sequencing more mitogenomes at various taxonomic levels will also improve our understanding of mitogenomic evolution and phylogeny in Cercopidae.

     

The seed dispersal catapult of Cardamine parviflora (Brassicaceae) is efficient but unreliable

? Premise of the study: Seed dispersal performance is an essential component of plant fitness. Despite their significance in shaping performance, the mechanical processes that drive dispersal are poorly understood. We have quantified seed dispersal mechanics in Cardamine parviflora (Brassicaceae), a ballistic disperser that launches seeds with specialized catapult-like structures. To determine which aspects of catapult function dictate interspecific dispersal differences, we compared this disperser with other ballistic dispersers. Comparison with brassicas that lack ballistic dispersal may also provide insight into the evolution of this mechanism. ? Methods: Catapult performance was quantified using high-speed video analysis of dehiscence, ballistic modeling of seed trajectories, and measuring the mechanical energy storage capacity of the spring-like siliqua valve tissue that launched the seeds. ? Key results: The siliquae valves coiled rapidly outward, launching the seeds in 4.7 ± 1.3 ms (mean ± SD, N = 11). Coiling was likely driven by the bilayered valve structure. The catapult was 21.3 ± 10.3% efficient (mean ± SD, N = 11) at transferring stored elastic energy to the seeds as kinetic energy. The majority of seeds (71.4%) were not launched effectively. ? Conclusions: The efficiency of the C. parviflora catapult was high in comparison to that of a ballistic diplochore, a dispersal mode associated with poor ballistic performance, although the unreliability of the launch mechanism limited dispersal distance. Effective launching requires temporary seed-valve adhesion. The adhesion mechanism may be the source of the unreliability. Valve curvature is likely driven by the bilayered valve structure, a feature absent in nonballistic brassicas.     

Molecular signatures of divergence and selection in closely related pine taxa

Efforts to detect loci under selection in plants have mostly focussed on single species. However, assuming that intraspecific divergence may lead to speciation, comparisons of genetic variation within and among recently diverged taxa can help to locate such genes. In this study, coalescent and outlier detection methods were used to assess nucleotide polymorphism and divergence at 79 nuclear gene fragments (1212 SNPs) in 16 populations (153 individuals) of the closely related, but phenotypically and ecologically distinct, pine taxa Pinus mugo, P. uliginosa and P. uncinata across their European distributions. Simultaneously, mitochondrial DNA markers, which are maternally inherited in pines and distributed by seeds at short geographic distance, were used to assess genetic relationships of the focal populations and taxa. The majority of nuclear loci showed homogenous patterns of variation between the taxa due to a high number of shared SNPs and haplotypes, similar levels of polymorphism, and low net divergence. However, against this common genetic background and an overall low population structure within taxa at mitochondrial markers, we identified several genes showing signatures of selection, accompanied by significant intra- and interspecific divergence. Our results indicate that loci involved in species divergence may be involved in intraspecific local adaptation.     

Comparison of the primary structure ofwaxy proteins (granule-bound starch synthase) between polyploid wheats and related diploid species

Thewaxy proteins encoded by the genomes A, B, and D in polyploid wheats and related diploid species were isolated by SDS-PAGE. The N-terminal amino acid sequences of mature proteins and V8 protease-induced fragments were determined. A total of five amino acid substitutions was detected in these sequences, which represent about 10% of the whole sequences of thewaxy proteins. A comparison of these sequences in polyploid wheats with those in related diploid species revealed the following: (i)waxy proteins encoded by the A genome of polyploid wheats were identical to that ofTriticum monococcum, (ii) thewaxy protein encoded by the B genome ofT. turgidum was identical to that ofT. searsii, but differed from those ofT. speltoides andT. longissimum by one amino acid substitution, (iii) thewaxy protein encoded by the B genome ofT. aestivum differed from that encoded by the B genome ofT. turgidum by one amino acid substitution, and (iv) thewaxy protein encoded by the D genome ofT. aestivum was identical to that ofT. tauschii.