A comparison of nuclear and mitochondrial cline shapes in a hybrid zone in the Sceloporus grammicus complex (Squamata; Phrynosomatidae)

The F5 and FM2 chromosome races of the Sceloporus grammicus complex form a hybrid zone in the Mexican state of Hidalgo. Previous studies of this zone have assessed genetic structure by averaging estimates of shape and width across three diagnostic chromosome markers. This approach is likely to mask subtle differences in cline shape among loci (e.g. selected vs. neutral), and obscure any displacement of cline centres (if present). Here we use maximum likelihood methods to construct the best fitting individual clines for three chromosomal markers, and also add two new markers; the mitochondrial DNA (mtDNA) locus, and the nuclear ribosomal DNA (rDNA) repeat. For each locus, hybrid zone models were fitted by cline shape and width, and the position and number of segments describing the centre of the zone. Pairwise comparisons between all clines revealed concordance between chromosomes 2 and 6, but significant discordance in cline structure among all other paired combinations. The concordance of chromosomes 2 and 6 suggests that these clines are maintained by genome-wide forces. The discordance of the chromosome 1 cline suggests an influence of asymmetric introgression, while the mtDNA cline is probably influenced by selection and drift. The rDNA locus reveals a pattern best explained by either extreme asymmetric introgression or gene conversion. The structure of zone indicates that genome-wide processes and locus specific selective forces as well as drift, are operating to different degrees on different loci. The locus-by-locus approach used here permits a finer discrimination among possible mechanisms responsible for the maintenance of the individual clines.     

Cytological identification of the genomes in pentaploidAllium neapolitanum using Giemsa C-banding

Two homoeologous sets of chromosomes in pentaploidAllium neapolitanum Cyr. (Liliaceae) are recognizable by their C-bands. The banding pattern is the same for one Californian and five Yugoslavian populations, suggesting a common chromosomal origin. Predominant meiotic association of identically banded homologues indicates a genomic formula of AA A_I BB, confirms an allopolyploid origin, and argues against genetically controlled pairing.     

Those amazing dinoflagellate chromosomes

Dinoflagellates are a very large and diverse group of eukaryotic algae that play a major role in aquaticfood webs of both fresh water and marine habitats. Moreover, the toxic members of this group posea health threat in the form of red tides. Finally, dinoflagellates are of great evolutionary importance,because of their taxonomic position, and their unusual chromosome structure and composition. While the cytoplasm of dinoflagellates is typically eukaryotic, the nucleus is unique when compared to the nucleusof other eukaryotes. More specifically, while the chromosomes of all other eukaryotes contain histones,dinoflagellate chromosomes lack histones completely. There are no known exceptions to this observation: all dinoflagellates lack histones, and all other eukaryotes contain histones. Nevertheless, dinoflagellates remain a relatively unstudied group of eukaryotes.     

Banding pattern of A and B chromosomes of Prochilodus lineatus (Characiformes, Prochilodontidae), with comments on B chromosomes evolution

B chromosomes in Prochilodus lineatus, a migratory neotropical fish, were analyzed in a comparative study among populations from the Dourada lagoon (State of Paraná, Brazil) and from Mogi-Guaçu river (State of São Paulo, Brazil). The data on C-banding and fluorescent in situ hybridization with a satellite DNA probe (SATH1), indicate that the small metacentric B chromosome might correspond to an isochromosome. On the other hand, both populations presented a distinct set of B chromosomes, differentiated either by their number and by the presence of variant B types in the population from Mogi-Guaçu river. The present results indicate that the B chromosomes of P. lineatus should have an ancient origin, and have undergone a differential evolutionary pathway among distinct populations.     

The vanishing clone: karyotypic evidence for extensive intraclonal genetic variation in the peach potato aphid,Myzus persicae (Hemiptera: Aphididae)

Analysis of holocentric mitotic metaphase chromosomes of the peach‐potato aphid Myzus persicae (Sulzer) clone 33H revealed different chromosome numbers, ranging from 12 to 17 within each embryo, in contrast to the standard karyotype of this species (2n = 12). Chromosome length measurements revealed that the observed chromosomal mosaicism is the result of recurrent fragmentations of chromosomes X, 1 and 3 because of fragile sites or hot spots of recombination. Fluorescent in situ hybridization experiments showed that X chromosomes were frequently involved in recurrent fragmentations, in particular their telomeric end opposite to the nucleolar organizer region. Experiments to induce males showed that M. persicae clone 33H is obligately parthenogenetic. The reproduction by apomictic parthenogenesis, together with a high telomerase expression that stabilized the chromosomes involved in the fragmentations observed in the M. persicae clone 33H, appears to favour the stabilization of the observed chromosome instability. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 350–358.     

Specific features of meiosis in the Siberian fir (<Emphasis Type="Italic">Abies sibirica</Emphasis> Ledeb.) artificial populations

Meiosis was studied in the Siberian fir (Abies sibirica Ledeb.) at the arboretum of the Sukachev Institute of Forest. Specific features of meiosis in planted trees have been described. Both general and specific types of irregularities have been identified. The range of irregularities under the arboretum conditions was much wider than in natural ecosystems.     

A Cytogenetic Study of the Leaf Beetle Genus Cyrtonus (Coleoptera, Chrysomelidae)

The chromosomes of ten species of Cyrtonus and the genome sizes of six are surveyed. Among the total of 15 chromosomally studied species, 11 have 2n=28 chromosomes and a 13+Xy_p male meioformula, three have 2n=40 and 19+Xy_p and one 2n=46 and 22+Xy_p. All but one species with 28 chromosomes show only metacentric or submetacentric chromosomes, whereas the species with 40 and 46 chromosomes display some telocentrics or subtelocentrics, that are probably derived from the former by centric fissions. However, since the number of major chromosome arms is strikingly higher in these latter species (NF=70 and 78) than in the 28-chromosome species (mostly NF=56), other chromosomal rearrangements such as pericentric inversions or heterochromatin accretions could also be involved. The genome sizes display a narrow range, from 1C=0.6–1.22pg, and they are not significantly correlated with the chromosome numbers. Some possible factors implied in the rough chromosomal evolution of Cyrtonus are discussed in relation to a few other genera of the subfamily Chrysomelinae.     

Karyotype morphology and cytogeography in Brunnera and Cynoglottis (Boraginaceae)

A comparative study of karyotype morphology and heterochromatin patterns in Brunnera and Cynoglottis (Boraginaceae) was carried out with traditional methods and Giemsa C-banding. Two polymorphic species of Cynoglottis , each with two subspecies, and two of Brunnera were investigated using native population samples from the central-eastern Mediterranean and Middle East. Pollen size of these samples was measured to investigate relationships with ploidy level. C. barrelieri subsp. barrelieri and subsp. serpentinicola are characterized by In = 18 and smaller pollen grains in contrast to C. chetikiana subsp. chetikiana and subsp. paphlagonica , which are fundamentally tetraploid with 2n = 36. The occurrence of cytotypes with 2n –/2 and 2n = 24 in both subspecies of C. chetikiana , however, would suggest x = 6 as the original haploid number and x = 9 as a derived one. Furthermore, the finding of a hypoploid cytotype with 2n = 16 in C. barrelieri ssp. barrelieri was consistent with previous reports and suggested relationships with Anchusa. Karyoevolutionary processes possibly associated with such a wide chromosome variation in Cynoglottis are discussed. Brunnera macrophylla and B. orientalis share a complement of 2n= 12 and an apparently identical karyotype, which differs from Cynoglottis in terms of asymmetry, chromosome size and morphology. A basic C-banding style was present in Brunnera and Cynoglottis , but heterochromatin content increased from the former to the latter. The parallel increase in chromosome number, heterochromatin content and size of the pollen from Brunnera to Cynoglottis may reflect an evolutionary progression, and is consistent with the supposed ancient origin of Brunnera.