Cytogenetics of ticks (Acari: Ixodoidea)

Haemaphysalis longicornis consists of diploid bisexual races (20+ XX; 20+X), triploid obligatory parthenogenetic races (30–35 chromosomes) and an aneuploid race capable of bisexual and parthenogenetic reproduction (22–28 chromosomes). Karyotypes were analyzed for each race. Hybridization failed between diploid and triploid races, but succeeded between bisexual diploid males and parthenogenetic aneuploid females. F₁ and F₂ progeny were produced and their chromosomes studied. Crossing of F₁ progeny to a bisexual race was successful. Parthenogenetic ability was almost completely lost in F₁ and F₂ females. Several possible modes of evolution from diploid bisexual individuals to triploid parthenogenetic ones are discussed as is species characterization in taxa with races reproducing bisexually, parthenogenetically and by a combination of both methods.Supported in part by National Science Foundation Research Grant GB-21008, National Institute of Allergy and Infectious Diseases (NIH) Grant 09556 and the United States Army Medical Research and Development Command, Office of The Surgeon General, Department of the Army, Washington, D. C. 20315, U.S.A.     

Chromosome banding in Cacopsylla mali (Schmidberger) and Cacopsylla sorbi (Linnaeus) (Homoptera, Psyllidae) with polymorphic sex chromosomes

C-banding and Ag staining were applied to Cacopsylla sorbi and C. mali. The aim was to discover some additional cytological markers to follow the pathways of the sex determination system transformation in the evolution of the species. Of three karyotype patterns so far described in the literature for these species--a type A (XO), B (neoXY) and C (neoX1X2Y), only the last two types (B and C) were found. All 6 studied Cacopsylla sorbi from Finland had a karyotype of type B (2n = 20 + XY), while C. mali had both types. Type B (2n = 22 + XY) was observed in 31 males, whereas type C (2n = 20 + neoX1X2Y) in the remaining four. The karyotype of C. sorbi was found to be characterized by a very small amount of C-positive material, localized in a telomere of the Y chromosome. The karyotype of C. mali was also characterized by a very small amount of C-banded material. Both the sex chromosomes and the autosomes displayed a marked polymorphism of C-positive bands within different individuals and even the same individual. In both species the nucleolus was located in the telomere of a middle sized autosomal till diplotene inclusive. The C-banding and Ag staining in the studied Cacopsylla species did not provide any additional cytological markers for an understanding of the pathways of sex determination system transformation in the evolution of the species.     

Discovery of a diploid population of theHemidactylus garnotii-vietnamensis complex (Reptilia: Gekkonidae)

A diploid member of the parthenogenetic gekkonid species complexHemidactylus garnotii-vietnamensis was discovered for the first time from Thailand. This gecko, seemingly unisexual and parthenogenetic, possesses 2n=2x=38 chromosomes, showing distinct heteromorphisms. The absence of bisexual congeneric species with a combination of karyomorphs to produce this karyotype indicates the occurrence of chromosomal rearrangements after the initial estabilishment of a diploid clonal lineage of hybrid origin. Results of karyotypic comparisons of the present sample and the three known triploid species belonging to theH. garnotii-vietnamensis complex suggest that a triploid karyomorph similar to that ofH. vietnamensis has first emerged through an insemination of the diploid parthenogen's egg by the sperm from a bisexual species having 44 chromosomes (all telocentric), and that the karyomorph subsequently experienced some minor chromosomal aberrations to produce the karyomorphs ofH. vietnamensis andH. garnotii. The origin of theH. stejnegeri karyotype still remains an open question for future studies.     

A comparative cytological investigation of the reproductive cycle of an amphimictic diploid and a parthenogenetic triploid form of Lumbricillus lineatus (O.F.M.) (Oligochaeta,Enchytraeidae)

Summary The cytology of a diploid amphimictic (2x=26) and a triploid parthenogenetic (3x=39) cytotype of Lumbricillus lineatus has been described. The triploid type never produces mature sperm, but it must be fertilized by sperm from the diploid cytotype in order to produce viable eggs. However, the sperm does not enter the egg, but eggs which have not been activated by sperm die at an early stage. Oogenesis in the triploid cytotype, which results ultimately in the restoration of the somatic chromosome number, follows a pattern which has not been described in other parthenogenetic organisms. The first meiotic division is asynaptic and no typical metaphase plate is formed; the univalents are distributed to opposite poles without undergoing an equational division. The first division is therefore numerically approximately reductional. The nuclei are at anaphase when the eggs leave the animal, whereas the nuclei of the diploid amphimictic cytotype are in MI when the eggs are laid. Following activation by spermatozoa, the first anaphase spindle is much elongated, and becomes V-shaped. The first anaphase spindle persists and no second anaphase spindle is formed. At the second division the chromosomes divide mitotically. The resulting four chromosome groups fuse two by two in such a way that two nuclei are formed each with the full somatic (triploid) chromosome set (cf. Figs. 14–16).The different steps involved in the evolution of this mechanism are discussed in relation to the evolution of the triploid cytotype.     

Cytotaxonomy of Dubyaea glaucescens (Compositae–Cichorieae)

Recent molecular phylogenetic analyses indicate that Dubyaea glaucescens (Compositae–Cichorieae) should be transferred to the genus Faberia as F. glaucescens. Here, we present cytological evidence for this transfer. Dubyaea glaucescens comprises two ploidy levels, 2n = 34 (diploid) and 2n = 51 (triploid), making the basic chromosome number x = 17. The chromosomes vary in length from 5.82 μm to 2.11 μm, and the karyotypes are 2n = 20m + 14sm (3sat) for the diploid cytotype and 2n = 30m + 21sm (3sat) for the triploid cytotype. Karyological characters of D. glaucescens, including chromosome number, size, morphology, and karyotype asymmetry, all agree remarkably with those reported previously in Faberia, but are distinct from those in other species of Dubyaea. The transfer of D. glaucescens to Faberia is thus strongly corroborated.     

三倍体短葶飞蓬的发现及其在育种上的意义

对云南省野生居群的短葶飞蓬有丝分裂的细胞学特征进行观察研究。在云南省大理苍山、腾冲杨家坪的二倍体野生居群中,发现有三倍体个体的存在。苍山居群的两种核型分别为2n=2x=18=4m 10sm 4st,2n=3x=27=6m 12sm 9st;杨家坪居群的两种核型分别为2n=2x=18=6m 10sm 2st,2n=3x=27=3m 15sm 9st。通过对其生物学特性及表型的分析,认为短葶飞蓬可以采取多倍体育种方式获得更优良的品种。     

Reproductive modes,ploidy distribution,and supernumerary chromosome frequencies of the flatworm Polycelis nigra (Platyhelminthes: Tricladida)

The hermaphroditic flatworm, Polycelis nigra, is characterized by two reproductive biotypes which differ with respect to ploidy; sexual individuals are diploid (n = 8, 2× = 16) and pseudogamous parthenogenetic individuals are polyploid (typically 3×). We have collected and karyotyped individuals from 15 sampling sites (13 in mid to northern Italy, one in Great Britain and one in The Netherlands). We found that biotypes can exist alone or in sympatry, and identified purely diploid, mixed diploid-polyploid, and purely polyploid populations. Karyotype data show that in addition to the normal autosome complement, B chromosomes of differing morphology as well as stable aneuploid chromosomes (extra-A) were found almost exclusively in polyploids (11 of 12 sites). We extensively sampled Lago di Toblino (northern Italy), a pure polyploid population characterized by a submetacentric to metacentric, mitotically stable B chromosome, as well as a stable extra-A chromosome. Here, individuals having 1–3 B chromosomes were more abundant (61%) than those having no B's, implying that B chromosome infection has little detrimental effect when occurring in low numbers. Furthermore, 66% of individuals from this population possessed extra-A chromosomes, although it is unclear whether these elements are aneuploid autosomes or B chromosomes of different morphology. The ubiquity of these chromosomes, within asexuals in particular, is suggestive of a correlation between the origination of the elements and the evolution of polyploidy, or may reflect increased tolerance of parthenogenetic genomes to aneuploidy. This revised version was published online in July 2006 with corrections to the Cover Date.     

The discovery of triploid Lycoris sprengeri Comes ex Baker from Anhui,China

Lycoris sprengeri Comes ex Baker is endemic to China. Reported in the present paper are the chromosomes number and karyotypes for two wild populations of the species from Anhui. ( 1 )Caishi population has a karyotype 2n=33=9st+21t+3T. The length of chromosomes ranges from 5.58～9.15μm. The karyotype belongs to Stebbin’s (1971) “4A”. (2)Longyashan populations have two karyotypes. The karyotype formula of the type I is 2n=22=8st+14t, with chromosomes ranging from 6.88～9.15μm. The karyotype belongs to “4A”. The karyotype formula of the type Ⅱ is 2n＝22＝1m+1sm+14st+6t, with chromosomes ranging from 7.20～15.80μm. The karyotype belongs to “3B”. The triploid type of L. sprengeri was discovered in Anhui for the first time. The karyotype 2n=22 =1m+1sm+14st+6t in diploid type of this species is here reported for the first time.The Robertsonian change plays a key role in karyotype evolution of Lycoris.     

Spontaneous triploidy and NOR activity in Eigenmannia sp. (Pisces,Sternopygidae) from the Amazon basin

The occurrence of a natural triploid among diploid individuals of Eigenmannia sp from the Amazon basin is described. The diploid individuals had 2n=31 and 32 chromosomes, the difference in chromosome number being due to a Robertsonian rearrangement. The triploid individual presented 2n=46 and had two fused acrocentrics. NOR activity was present in the three homologues of triploid and a NOR polymorphism was detected in the triploid and diploids.     

Cytotaxonomic study of genusHymenasplenium (Aspleniaceae) in Xishuangbanna, Southwestern China

The gametic chromosome numbers of sevenHymenasplenium (Aspleniaceae) species from Xishuangbanna, Yunnan Prov., China, were investigated. All the examined individuals ofH. obscurum, H. cheilosorum andH. latipinnum were sexual diploids with n=39 chromosomes. Intraspecific cytological variation was found inH. excisum, which has a sexual diploid (n=39) and a tetraploid (n=78). Only a triploid apogamous cytotype (n=ca.117) was found inH. laterepens. Hymenasplenium apogamum showed the most complicated intraspecific variation and included a sexual diploid (n=39), a sexual tetraploid (n=78) and an apogamous triploid (n=ca.117). This work reports for the first time the sexual diploids ofH. cheilosorum andH. apogamum, which are only apogamous elsewhere in east Asia, Himalayas and Indochina. These results may indicate that this area is one of the diversity centers ofHymenasplenium. Most of the above species have chromosome numbers based on x=39. In contrast,H. costarisorum contains a sexual diploid (n=36) and a sexual tetraploid (n=72), indicating that its basic number is x=36.     

The karyotype of Nothoscordum arenarium Herter (Gilliesioideae, Alliaceae): A populational and cytomolecular analysis

The genus Nothoscordum Kunth comprises approximately 20 species native to South America. Karyologically, the genus is remarkable for its large chromosomes and Robertsonian translocations. Variation in chromosome number has been recorded in a few polyploid species and it is unknown among diploids. This study presents the chromosome number and morphology of 53 individuals of seven populations of N. arenarium Herter (2n = 10). In addition, karyotype analyses after C-banding, staining with CMA and DAPI, and in situ hybridization with 5S and 45S rDNA probes were performed in six individuals from one population. All individuals exhibited 2n = 10 (6M + 4A), except for one tetraploid (2n = 20, 12M + 8A) and one triploid (2n = 15, 9M + 6A) plant. C-banding revealed the presence of CMA(+) /DAPI (-) heterochromatin in the short arm and in the proximal region of the long arm of all acrocentric chromosomes. The 45S rDNA sites co-localized with the CMA (+) regions of the acrocentrics short arms, while the 5S rDNA probe only hybridized with the subterminal region of a pair of metacentric chromosomes. A change in the pattern of CMA bands and rDNA sites was observed in only one individual bearing a reciprocal translocation involving the long arm of a metacentric and the long arm of an acrocentric chromosome. These data suggest that, despite isolated cases of polyploidy and translocation, the karyotype of N. arenarium is very stable and the karyotypic instability described for other species may be associated with their polyploid condition.     

Occurrence of natural triploidy in Rhamdia quelen (Siluriformes, Heptapteridae)

Five specimens of Rhamdia quelen collected from the Lindóia Stream, PR, Brazil, were cytogenetically analyzed. The diploid chromosome number found was 58, including 30 metacentric, 16 submetacentric, 10 subtelocentric, and 2 acrocentric chromosomes. Supernumerary or B chromosomes, frequently observed in this fish group, were not detected. One of the individuals was triploid, with 3n = 87. A silver-stained nucleolar organizer region was found on a pair of submetacentric chromosomes of the diploid specimens, and on three chromosomes of the triploid individual, confirming triploidy. Treatment with fluorochrome chromomycin A(3) revealed fluorescent bands coincident with those of the silver-stained nucleolar organizer region, in both diploid and triploid individuals, showing that this is a GC-rich region. Heterochromatin distribution was visualized by the C-banding technique, mainly in the terminal chromosome regions of the individuals and was also observed in the pericentromeric regions of some chromosomes and at both telomeres.     

中国淡水三角涡虫染色体变化与生殖的关系

利用空气干燥法对淡水三角涡虫的染色体进行研究。结果表明：三角涡虫的染色体数目为n=8,2n=16,2n=24,为二倍体2n=2x=16、三倍体2n=3x=24和混合倍体2n=2x=16,2n=3x=24,有时也可见到非整倍体。以有性生殖为主的类群．有性生殖期间有性个体大量存在,生殖器官比较发达．染色体为二倍体;以无性生殖为主的类群,很少出现有性个体,染色体为三倍体;既有有性生殖又有无性生殖的类群,有性生殖期间,生殖器官发育稍差,染色体主要为混合倍体．有时出现二倍体或三倍体。本文对影响三角涡虫性成熟的因素也进行了讨论。     

Giant-sized chromosomes in genus Phyllobrotica Chevrolat 1837 (Coleoptera: Chrysomelidae: Galerucinae) and parthenogenesis in P. adusta (Creutzer 1799)

Only females were detected in a small population of Phyllobrotica adusta (Creutzer 1799) (Chrysomelidae: Galerucinae) located in a mountain near Kastoria (Greece). Their karyotype, composed of 42 chromosomes, including three giant-sized ones, is assumed to be triploid. Only two giant-sized chromosomes were present in the 37,X/38,XX karyotype of the congeneric sexual species P. quadrimaculata (L. 1758). Although males were described in P. adusta, the abnormal sex ratio, the presumed triploidy and the absence of spermatozoa in the spermatheca strongly suggest a parthenogenetic reproduction of the population studied. Both parthenogenesis and giant-sized chromosomes have been described independently in some species of Neotropical and Palearctic Galerucinae, but never together.     

Structural heterozygosity in parthenogenetic populations of Cnemidophorus lemniscatus (Sauria,Teiidae) from the Amazonas valley

C. lemniscatus is the only species of the genus Cnemidophorus found in the Amazonas valley. Among the populations from 15 localities which were studied, 5 included individuals of both sexes, but the remaining 10 were composed only by parthenogenetic females. In every case the all-female populations presented one or more heteromorphic pairs of chromosomes; in no case did this happen in the sexual populations. Five different karyotypes were described but no two of them were present in the same locality. No triploid individuals were found. A hypothesis for explaining this situation is discussed. It is probable that the chromosomes of the ancestral sexual population presented structural balanced polymorphisms preserved by heterosis or by better adaptation of each homozygote to a different niche. The latter case explains better the finding of different karyotypes without heteromorphism in different bisexual populations. When occasional parthenogenesis happened to appear in an heterotic structural heterozygote a successful strain could be established which would displace its bisexual competitors.     

Morphological comparisons and hypotheses on the origin of polyploids in parthenogenetic Fasciola sp

It is known that Fasciola sp. from Japan and the Republic of Korea consist of diploids (2n = 2x = 20), triploids (2n = 3x = 30), and mixoploids with diploid and triploid cells. Triploids are distributed over Asia and Hawaii. Abnormal spermatogenesis and parthenogenetic reproduction are the main characteristics of Fasciola sp. Here we measured 21 different morphological parameters of diploid and triploid flukes of Fasciola sp. obtained from Japan and the Republic of Korea. Statistical analysis showed that diploid and triploid flukes were morphologically different. No bivalents or trivalents could be detected in diploid and triploid flukes, respectively. Based on our findings, we speculate that parthenogenetic diploids, triploids, and mixoploids (2x/3x) of Fasciola sp. are genetically related to each other.     

Oogenesis and the Chromosomes of the Cystoid Nematode,Meloidodera floridensis

Three Meloidodera floridensis populations of different geographic or host origin all reproduced by mitotic parthenogenesis. One of them from pine had a somatic chromosome number of 26, whereas, another population from pine and one from azalea had 2n = 27 chromosomes. All are considered to be triploid forms derived from an amphimictic ancestor with n = 9 chromosomes, the basic number in the closely related genus Heterodera. Evidence is presented which suggests that during division the chromosomes of the germ-line cells of the developing embryo behave differently than the chromosomes of all other blastomeres.     

The Biology of Allium monanthum (Liliaceae) I. Polyploid Complex and Variations in Karyotype

Abstract Plants of Allium monanthum Maxim., whose gender expression are usually dioecious, but rarely hermaphrodite or gynomonoecious, proved to constitute a polyploid complex, consisting of diploid, triploid, and tetraploid individuals. The basic chromosome complement of this species consists of seven metacentric or submetacentric chromosomes and one acrocentric, the latter possessing a satellite on the short arm. Thus, the karyotype formula is expressed as 7V+11 (x=8). The diploid plants (2n = 16) were confined to central Honshu, Japan. Typical female plants possessed the standard karyotype, whereas male plants were heterozygous for two kinds of translocations. The 3x plants (2n=24) are somewhat widely distributed in the areas from the Kanto to Hokuriku district in Honshu. All female triploid plants possessed the standard karyotype. The geographical distribution of 4x plants (2n=32) which express mostly a female phenotype occurred nearly throughout the whole areas investigated; they are geographically isolated from the 2x plants. A majority of 4x plants had the standard karyotype. The remaining tetraploids were of the aberrant type, 4x/51, which has five acrocentric chromosomes, and two aneuploids 4x+1 and 4x-1. Both 3x and 4x forms seem to be of autopolyploid origin. Three kinds of aberrant nucleolar chromosomes with an extra satellite or an inseried secondary constriction were found in the heterozygotes for translocations of 2x plants and also in some plants of the 3x form. These aberrant plants usually form their own homogeneous populations, but were somewhat scattered throughout the range in their distribution. Thus, these individuals are considered to have perpetuated these types of chromosome aberrations which originated in the remote past.     

Multiple supernumerary chromosomes in the pseudogamous parthenogenetic flatworm Polycelis nigra: lineage markers or remnants of genetic leakage?

Polycelis nigra is a free-living simultaneous hermaphroditic flatworm that has amphimictic and pseudogamous parthenogenetic biotypes. Sexual individuals are always diploid (2n = 16) and pseudogamous parthenogens are polyploid (usually triploid). Two types of supernumerary chromosomes are found in parthenogens, those resembling autosomes ("A-like") and typical B chromosomes, both of which reach frequencies in populations of close to 100%. Experiments measuring the transmission rates of the B chromosomes indicated that they are potentially inherited via the male line, escaping expulsion by pseudogamous parthenogenesis. This study used the C-banding technique to demonstrate (i) that there is a single morphologically distinct B chromosome (B1) and (ii) that there are two "A-like" chromosomes that can be considered B chromosomes (B2 and B3) and which are not simple polysomics of one of the eight autosomes. As there is no genetic exchange between pseudogamous parthenogenetic lineages, two different individuals carrying a similar B morph must either have received it through common ancestry (a lineage marker) or have acquired it horizontally from another parthenogenetic lineage (leakage). C-banding further revealed intra-individual heteromorphy for band regions on chromosomes 5 and 8. This supports the karyotypic observation that oogenesis is preceded by premeiotic chromosome doubling followed by pairing of replicate homologues.     

Occurrence of macro B chromosomes in Astyanax scabripinnis paranae (Pisces,Characiformes, Characidae)

B chromosomes occur in several Neotropical fish species. Cytogenetic analysis of 27 specimens (15 females and 12 males) of Astyanax scabripinnis paranae from the Araquá river (a small headwater tributary of the Tietê river) shows that this population has 2n=50 chromosomes (4M+30 SM+4ST+12A), two chromosome pairs with NORs and conspicuous C-band positive blocks in the terminal position of the long arm of four chromosome pairs. In this population, eight females presented 2n=51 chromosomes and the extra chromosome was a large metacentric similar in size and morphology to the first chromosome pair in the karotype. This accessory chromosome is entirely heterochromatic in C-banded metaphases and shows a late replication pattern evidenced by BrdU incorporation. There was no significant correlation between the presence of B chromosomes and increased NOR activity at the P>0.05 level. Some aspects related to these B chromosomes are discussed.