Chromosomal polymorphism in the Atlantic dog-whelk, Nucella lapillus (Gastropoda: Muricidae): nomenclature, variation and biogeography

Nucella lapillus appears to be unique within the Muricidae, and indeed the Mollusca, in exhibiting a Robertsonian chromosomal polymorphism. The recorded diploid values range from 2 n  = 26 to 2 n  = 36, putatively brought about by fusion of smaller chromosomes to form five pairs of large metacentrics in the 2 n  = 26 form. In this study, the karyotypes of the numerically extreme forms (2 n  = 26 and 2 n  = 36) have been illustrated and described in detail, and a new scheme of nomenclature is proposed for the chromosomal rearrangements observed in N. lapillus . Chromosome numbers and karyotypes were recorded and analysed from 70 sites throughout its wide geographical range, mainly from around the UK coasts but also from sites in Norway, France, Spain, Portugal and the USA, showing remarkable variation in both diploid number and karyotypic configuration. The results provide new evidence that seven chromosomes in the 2 n  = 26 form can be involved in the Robertsonian rearrangements, but the maximum recorded diploid number remains 2 n  = 36. Inversions were confirmed in three chromosomes and one population was found to exhibit aneuploidy. Possible explanations for the geographical trends in karyotypic variation are discussed, but despite the advances in the karyology of N. lapillus , a simple solution to this enigmatic phenomenon remains elusive.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 195–210.     

Cytotaxonomy of species of Vernonia, section Lepidaploa, group Axilliflorae (Asteraceae, Vernonieae)

Mitotic chromosomes of eight populations of six species of Vernonia sensu Baker (Asteraceae, Vernonieae, section Lepidaploa , group Axilliflorae ) were studied to assess the validity of maintaining the genus as proposed currently ( sensu Baker) or of splitting it into several smaller genera ( sensu Robinson). The species were collected in areas of 'cerrado' and 'campo rupestre' in southern and central-western Brazil. The chromosome numbers were 2 n  = 20–40 and karyotypic analysis showed a predominance of metacentric chromosomes, with some submetacentrics. B chromosomes were seen in one population of V. geminata . The chromosomes varied in length from 0.9 to 4.6 µm, with a total chromatin length of 29.7–45.0 µm and a symmetry index of 41.2–46.9%. The intrachromosomal asymmetry index varied from 0.13 to 0.29, and the interchromosomal asymmetry index varied from 0.15 to 0.21. The dispersion diagram showed that population 1 of V. geminata had the most asymmetrical karyotype. These results do not provide sufficient evidence for a conclusive cytotaxonomic discussion of Vernonia , mainly because of the impossibility of associating any infrageneric group with specific karyotypic characters, and also because of the small number of species analysed so far.  © 2007 The Linnean Society of London. Botanical Journal of the Linnean Society , 2007, 154 , 99–108.     

Cytology, palynology, and taxonomy of Asteropyrum and four other genera of Ranunculaceae

A karyomorphological study of two species in Asteropyrum (Ranunculaceae) and five in presumably related genera (one each in Caltha , Coptis , and Dichocarpum and two in Thalictrum ) reveals close similarities between Asteropyrum and Caltha , but obvious differences between Asteropyrum and Coptis , Dichocarpum , and Thalictrum , in some karyological features, such as the structure of the interphase nuclei, chromosome size, basic chromosome number, and condensation behaviour of chromosomes during the mitotic prophase. The chromosomes of Asteropyrum are categorized as being of the R-type and the basic chromosome number is confirmed as x  = 8, indicating a possible close affinity of Asteropyrum to members in the subfamily Helleboroideae, in particular to Caltha and its allies. Asteropyrum peltatum and Asteropyrum cavaleriei are shown to be more or less differentiated from each other in gross morphology and palynology, and somewhat independent in geographical distribution, albeit with intermediate forms occurring where their distribution zones overlap. It seems justifiable to treat them as two subspecies of A. peltatum .  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 15–26.     

Karyotype analysis in South American species of Myrtaceae

In Myrtaceae (Myrteae), the diploid chromosome number 2 n  = 2 x  = 22 is the most common, although variations of ploidy level occur, with some triploid (2 n  = 3 x  = 33) and tetraploid (2 n  = 4 x  = 44) records. Karyotype details in this group are scarce because the chromosomes are small (< 2 μm). In this work, we carried out a karyotypic analysis of 15 species of Myrtaceae grouped in different subtribes and genera. Measurements of chromosome length (long arm, L ; short arm, S ) were taken and several karyotypic parameters were calculated for each species. The karyotypes in fleshy-fruited taxa (Myrteae) were more varied than in the other previously analysed dry-fruited group ( Eucalyptus , Eucalypteae), in which the chromosomes were exclusively metacentric.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 571–580.     

Chromosomes of four species in three genera of Commelinaceae from China and their systematic implications

Chromosomes of four species in three genera of Commelinaceae from China were examined. Spatholirion longifolium had 2 n  = 20. This small genus is considered to be of a possible polyploid origin based on x  = 5, a basic number shared by its closest ally, the monospecific genus Streptolirion , with its only species having 2 n  = 10. The two genera were found to be very different from each other in their karyotypic constitution. The differences in both chromosome number (2 n  = 20 vs. 10) and karyotypic constitution support their separation as two independent genera. The remaining three species, Amischotolype hispida , Porandra ramosa and P. scandens , all had 2 n  = 36. In view of the occasional occurrence of 2 n  = 18 in the African Coleotrype , a genus very close to Amischotolype and Porandra in gross morphology, these three species are all very probably polyploid based on x  = 9. The high degree of karyotypic similarity of the three genera also strongly indicates their close affinity and supports their placement in the subtribe Coleotrypinae. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 399–403.     

Cytotaxonomy of Begonia rubropunctata and B. purpureofolia (Begoniaceae)

The chromosome numbers of four Chinese Begonia species were counted for the first time as follows: 2 n  = 22 in B. rubropunctata , 2 n  = 18 in B. purpureofolia , 2 n  = 44 in B. pedatifida , and 2 n  = 22 in B. villifolia . The first two species had relatively large chromosomes with early condensed chromatin in the distal and interstitial or proximal regions, whereas the last two had small chromosomes with early condensed chromatin in the proximal regions. Although they have been reduced in the literature to synonyms of B. pedatifida and B. villifolia , respectively, B. rubropunctata and B. purpureofolia should be treated as distinct species because of the differences in chromosome numbers and other chromosome features.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 513–517.     

Karyology of some Brazilian species of Alismataceae

The family Alismataceae ( sensu Cronquist) comprises 11 genera and 75 species of aquatic and semiaquatic herbs. In Brazil, only the two most speciose genera, Echinodorus Rich. ex Engelm. and Sagittaria L., are present. The chromosome number 2 n  = 22 is common to all species. We present karyotypes for eight species, together with their asymmetry index (TF%) and total chromatin length (TCL). All karyotypes have high karyotypic asymmetry and TCL, due to their large and mostly acrocentric chromosomes. The chromosomal evolution of the Alismatidae group is discussed.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 159−164.     

Chromosomal variability in the genus Primula (Primulaceae)

Chromosome numbers and measurements were recorded in 47 individuals of ten taxa of Primula , representing eight species and two subspecies from ten populations. The basic numbers of chromosomes were x  = 8, 9 or 11, and they were mostly metacentric, medium-long to medium-small, ranging in length from c . 3.6 µm to 1.6 µm. Diploid chromosome numbers of 2 n  = 2 x  = 24 and 22 were scored for the first time in P. loeseneri Kitag. and P. prenantha Balf. & Sm., respectively. A new ploidy level of 2 n  = 4 x  = 44 was found in P. burmanica Balf. & King. The recorded diploid numbers of the remaining species confirmed earlier reports. Interspecific variability in chromosome numbers was correlated with heterogeneity in their mean length. Comparison of the data with those in the literature revealed that the observed variability of chromosomal characters was compatible with the other taxonomic criteria and supports the current taxonomic delimitation. Chromosomal variation at the diploid level is the predominant feature in Primula evolution, and allopatric speciation has played a major role in its specific diversity. Subgen. Aleuritia could represent the main clade from which the other subgenera have evolved. The origin of the chromosome numbers, geographical distribution and evolution of the species were assessed, and the parallel polyphyletic mode of evolution in the genus was confirmed.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 211–219.     

Chromosome number, karyotype, and taxonomic considerations on the enigmatic Sellocharis paradoxa Taubert (Leguminosae, Papilionoideae, Genisteae)

Until recently, Sellocharis paradoxa Taubert, the only species of this Genisteae genus, was known solely by the isotypes. Recent new collections in Rio Grande do Sul, southern Brazil, have enabled data on chromosome number and karyotype morphology to be obtained for the first time. S. paradoxa has 2 n  = 20 chromosomes, and a bimodal asymmetrical karyotype, composed of one pair of long ( c . 6.3 µm) metacentric, five pairs of shorter acrocentric, and four pairs of shorter telocentric chromosomes ranging from c . 3.7 to 2.7 µm. The chromosome number and karyotype morphology of S. paradoxa do not fit into the Genisteae pattern. Existing information is so far insufficient to answer evolutionary questions about its origin and phylogenetic relationships, but the uniqueness of this taxon, first indicated by its peculiar leaf arrangement, and now supported by its uncommon karyological constitution, strongly suggests that the suprageneric taxonomic position of S. paradoxa should be re-evaluated.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 223–226.     

Evolution of karyotype,sex chromosomes,and meiosis in mygalomorph spiders (Araneae: Mygalomorphae)

Spider diversity is partitioned into three primary clades, namely Mesothelae, Mygalomorphae, and Araneomorphae. Mygalomorph cytogenetics is largely unknown. Our study revealed a remarkable karyotype diversity of mygalomorphs. Unlike araneomorphs, they show no general trend towards a decrease of 2n, as the chromosome number was reduced in some lineages and increased in others. A biarmed karyotype is a symplesiomorphy of mygalomorphs and araneomorphs. Male meiosis of some mygalomorphs is achiasmatic, or includes the diffuse stage. The sex chromosome system X₁X₂0, which is supposedly ancestral in spiders, is uncommon in mygalomorphs. Many mygalomorphs exhibit more than two (and up to 13) X chromosomes in males. The evolution of X chromosomes proceeded via the duplication of chromosomes, fissions, X–X, and X‐autosome fusions. Spiders also exhibit a homomorphic sex chromosome pair. In the germline of mygalomorph males these chromosomes are often deactivated; their deactivation and pairing is initiated already at spermatogonia. Remarkably, pairing of sex chromosomes in mygalomorph females is also initiated at gonial cells. Some mygalomorphs have two sex chromosome pairs. The second pair presumably arose in early‐diverging mygalomorphs, probably via genome duplication. The unique behaviour of spider sex chromosomes in the germline may promote meiotic pairing of homologous sex chromosomes and structural differentiation of their duplicates, as well as the establishment of polyploid genomes. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 377–408.     

Ribosomal, telomeric and heterochromatin sequences localization in the karyotype of Anemone hortensis

The karyotype of the Mediterranean species Anemone hortensis L. (Ranunculaceae) was characterized with emphasis on heterochromatin distribution and localization of ribosomal (18S−5.8S−26S and 5S rDNA) and telomeric repeats (TTTAGGG). Diploid chromosome complement, 2 n  = 2 x  = 16, common to all investigated populations, consisted of three acrocentric, one meta-submetacentric and four metacentric chromosomes ranging in size from 6.34 to 10.47 µm. Fluorescence in situ hybridization (FISH) with 18S and 5S rDNA probes revealed two 18S−5.8S−26S rDNA loci on a satellite and secondary constriction of acrocentric chromosome pair 2 and terminally on acrocentric chromosome pair 3, and two 5S rDNA loci in the pericentromeric region of meta-submetacentric chromosome pair 4 and in the proximity of the 18S−5.8S−26S rDNA locus on chromosome pair 2. The only GC-rich heterochromatin, as revealed by fluorochrome Chromomycin A3 staining, was that associated with nucleolar organizer regions, whereas AT-rich heterochromatin, stained with 4,6-diamino-2-phenylindole (DAPI), was distributed intercalarly and terminally on the long arm of all three acrocentric chromosomes, and terminally on chromosomes 4 and 5. FISH with Arabidopsis -type telomeric repeats (TTTAGGG) as a probe revealed two classes of signals, small dot-like and large bands, at chromosome termini exclusively, where they corresponded to terminal DAPI-stained heterochromatin. Heteromorphism of chromosome pair 4, which refers to terminal DAPI bands and FISH signals, was observed in populations of Anemone hortensis . Chromosome pairing during meiosis was regular with formation of localized chiasmata proximal to the centromere.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 177–186.     

Intrapopulation karyotypic variability in Allium roylei Stearn – a threatened species

Plants that are heterozygous for complex translocation from a small threatened population of Allium roylei Stearn from the Bani region of Jammu province (India) were analysed for karyotypic details. Somatic complements of all the plants analysed revealed heteromorphicity in one to three pairs of chromosomes. In addition, inter‐individual differences were observed regarding the presence or absence of one of the two nucleolar chromosomes, the positions that different heteromorphic chromosomal pairs occupy in the karyoidiograms and the extent of differences in various chromosomal pairs. The present paper records for the first time structural chromosomal polymorhism in A. roylei and highlights the probable mechanisms underlying the origin and establishment of this polymorphism. The extensive karyotypic variability seems to have originated through repeated interchanges involving a number of non‐homologous chromosomes. These anamolies are tolerated because there is no loss or gain of genes and, in addition, vegetative propagation is an efficient means of perpetuating the species. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 242–248.     

Karyological notes on eight species of Achillea L. (Asteraceae, Santolinoideae) from Turkey

The chromosome number and morphology of eight species belonging to the section Santolinoideae of the genus Achillea L. (Asteraceae) were investigated using karyological techniques. The species studied were Achillea cucullata (Hausskn.) Bornm., A. vermicularis Trin., A. monocephala Boiss. & Bal., A. boissieri (Hausskn.) Bornm., A. santolina L., A. gypsicola Hub.-Mor., A. goniocephala Boiss. & Bal., and A. spinulifolia Fenzl ex Boiss. In these species, the chromosome numbers were 2 n  = 18 in A. vermicularis , A. monocephala , and A. boissieri , 2 n  = 18A + 1B in A. spinulifolia , 2 n  = 36 in A. cucullata and A. santolina , and 2 n  = 54 in A. gypsicola and A. goniocephala . All of the chromosomes had median point (M), median region (m), or submedian (sm) centromeres. An increase in asymmetry was not observed in the karyotypes of the species.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 573–580.     

Analysis of molecular differentiation in a hybrid zone between chromosomally distinct races of the common shrew Sorex araneus (Insectivora: Soricidae) suggests their common ancestry

During postglacial colonization, populations that diverged in different refugia produced a patchwork of genomes, often delimited with sharp hybrid zones. The outcome of hybridization following the secondary contact of two genetically distinct populations is hard to predict. In this context, the present study investigated the genetic structure of the hybrid zone between the Drnholec and Białowieża chromosome races of the common shrew ( Sorex araneus ) in Poland using biparentally inherited (seven autosomal microsatellites) and uniparentally inherited (Y-linked microsatellite and mtDNA) molecular markers. On the basis of diagnostic chromosomes, the Drnholec and Białowieża races were classified to different karyotypic groups, which were believed to have independent glacial histories. It was found that genetic differentiation between the Drnholec and Białowieża races was weak and nonsignificant with respect to all molecular markers. However, these results are in contrast with the chromosomal structure of this hybrid zone. The very sharp frequency clines of the diagnostic chromosomes strongly suggest that gene flow between the Drnholec and Białowieża races was reduced. Nonsignificant correlations between genetic differentiation and both the presence of an environmental barrier and geographical distance reveal that only differences in karyotypes might be a reason for limited gene exchange between the races. It is assumed that a lack of molecular differences between the Drnholec and Białowieża races results from a shared ancestral variation.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 79–90.     

Ferulago trojana (Umbelliferae), a new species from western Turkey

Somatic chromosomes of four species of Ceratozamia , C. hildae , C. kuesteriana , C. mexicana and C. norstogii , and Stangeria eriopus , were observed and compared by the fluorescence in situ hybridization method using 5S ribosomal (rDNA) probes. The four Ceratozamia species and S. eriopus showed the same chromosome number of 2 n  = 16, and had similar karyotypes, comprising 12 metacentric (m), two submetacentric (sm) chromosomes and two telocentric (t) chromosomes. The four Ceratozamia species exhibited a proximal 5S rDNA site in the interstitial region of two m chromosomes. Stangeria eriopus exhibited a distal 5S rDNA site in the interstitial region of two m chromosomes, which probably indicates that the two genera differ in chromosome structure by at least one paracentric inversion. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 499–504.     

Chromosome studies in Hippeastrum (Amaryllidaceae): variation in genome size

This paper presents the karyotype and DNA content of 12 diploid species of Hippeastrum from South America. The variation in genome size is compared with the karyotype and DNA content of Amaryllis belladonna from South Africa. The Hippeastrum species present a uniform and bimodal basic karyotype formula, but significant differences are found in the total chromosome volume (TCV) and nuclear DNA content. A positive correlation between the DNA content and TCV is also observed. The karyotype's constancy is a product of changes in DNA content occurring in the whole chromosome complement. The DNA addition to the long and short sets of chromosomes varies independently. In species with higher DNA contents, the short chromosomes add equal DNA amounts to both arms, maintaining their metacentric morphology, whereas the long chromosomes add DNA only to the short arm, increasing the chromosome symmetry. These data show that the evolutionary changes in DNA amount are proportional to chromosome length, maintaining the karyotypic uniformity. A. belladonna has a larger DNA content and possesses a karyotype different from that of Hippeastrum spp., supporting the distinction between the two genera and upholding the name Amaryllis for the South African entity against Hippeastrum for the South American genus.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 171–178.     

Karyotypes of 16 populations of eight species in the genus Polygonatum (Asparagaceae) from China

The karyotypes of 16 populations belonging to eight species of Polygonatum from China were analysed. The chromosome numbers and karyotypes of P. omeiense, P. adnatum and P. hirtellum and the diploidy of P. tessellatum are reported for the first time. The basic chromosome numbers were x = 11, 13, 14 and 15. Based on Stebbins' karyotypic classification, the four karyotypes were recognized as 2B, 3B, 2C and 3C. Considering the arm ratio and individual chromosome size, it was concluded that the possible evolutionary trend of the karyotypes in Polygonatum was from 2B to 3C. The results show that: (1) satellite heterozygosity occurs in many species of this genus; (2) mixoploidy and B chromosomes occur in some species; and (c) karyotypes are different in different species and even in different populations of the same species. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 245–254.     

On the monophyly of Dactylorhiza Necker ex Nevski (Orchidaceae): is Coeloglossum viride (L.) Hartman a Dactylorhiza?

Previous phylogenetic analyses of Orchidaceae subtribe Orchidinae resulted in the proposal to classify Coeloglossum viride (L.) Hartman within the genus Dactylorhiza in order to maintain its monophyly. In this paper, we report some results that contradict previous studies regarding the monophyly of the traditional Dactylorhiza and its phylogenetic relationship with Coeloglossum. Our results, which combine sequences of the internal and external transcribed spacers of the nuclear ribosomal DNA, support the monophyly of Dactylorhiza , with Coeloglossum being a sister clade. The position of C. viride in the phylogenetic tree, and the considerable morphological differences with respect to Dactylorhiza , incline us to retain both lineages as distinct genera.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 261–269.     

Incipient speciation revealed in Anastrepha fraterculus (Diptera; Tephritidae) by studies on mating compatibility, sex pheromones, hybridization, and cytology

It has long been proposed that the nominal species Anastrepha fraterculus is a species complex and earlier studies showed high levels of pre-zygotic isolation between two laboratory strains from Argentina and Peru. Further experiments were carried out on the same populations and on their reciprocal hybrids, including pre- and post-zygotic isolation studies, pheromone analysis, and mitotic and polytene chromosome analysis. A high level of pre-zygotic isolation had been maintained between the parental strains despite 3 years of laboratory rearing under identical conditions. The level of pre-zygotic isolation was reduced in matings with hybrids. There were also differences in other components of mating behaviour. There were quantitative and qualitative differences in the sex pheromone of the two strains with the hybrids producing a mixture. The pre-zygotic isolation barriers were complemented by high levels of post-zygotic inviability and sex ratio distortion, most likely not due to Wolbachia , although there was evidence of some cytoplasmic factor involved in sex ratio distortion. Analysis of polytene chromosomes revealed a high level of asynapsis in the hybrids, together with karyotypic differences between the parental strains. The combined results of the present study indicate that these two strains belong to different biological entities within the proposed A. fraterculus complex.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 152–165.     

New or rarely reported chromosome numbers in taxa of subtribe Artemisiinae (Anthemideae, Asteraceae) from Mongolia

This study encompasses 25 chromosome counts of 18 species in the subtribe Artemisiinae (tribe Anthemideae) of the family Asteraceae, from Mongolia. Most (15 species) belong to Artemisia , the largest genus of the subtribe, whereas the others come from two genera very closely related to it: Ajania (two species) and Neopallasia (one species). Eleven counts are new reports, three are not consistent with previous reports and the remainder confirm scanty earlier information. The majority of the species have x  = 9 as their basic chromosome number, but there are some taxa with x  = 8. Ploidy levels range from 2 x to 6 x . The presence of B-chromosomes was detected in Ajania fruticulosa .  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 203–210.