Most cited article - PubMed ID 17362345
Unusual karyotype diversity in the European spiders of the genus Atypus (Araneae: Atypidae)
The mygalomorph spiders of the family Atypidae are among the most archaic spiders. The genus Atypus Latreille, 1804 occurs in Eurasia and northern Africa, with a single enigmatic species, Atypus snetsingeri Sarno, 1973, known only from a small area in southeastern Pennsylvania in eastern USA. A close relationship to European species could be assumed based on geographic proximity, but A. snetsingeri more closely resembled Asian species. This study was undertaken to learn more about the genetics of A. snetsingeri, its habitat requirements and natural history. Molecular markers (CO1 sequences) were compared to available data for other atypids and showed that A. snetsingeri is identical with A. karschi Dönitz, 1887 native to East Asia. Natural history parameters in Pennsylvania were also similar in every respect to A. karschi in Japan, therefore, we propose that the spider is an introduced species and the specific epithet snetsingeri is relegated to a junior synonym of A. karschi. Cytogenetic analysis showed an X0 sex chromosome system (42 chromosomes in females, 41 in males) and we also detected nucleolus organizing regions and heterochromatin, the latter for the first time in the Atypoidea. In Pennsylvania the spider is found in a variety of habitats, from forests to suburban shrubbery, where the above-ground webs are usually attached vertically to trees, shrubs, or walls, although other webs are oriented horizontally near the ground. Prey include millipedes, snails, woodlice, carabid beetles and earthworms. Atypus karschi is the first known case of an introduced purse-web spider. It is rarely noticed but well-established within its range in southeastern Pennsylvania.
BACKGROUND: Despite progress in genomic analysis of spiders, their chromosome evolution is not satisfactorily understood. Most information on spider chromosomes concerns the most diversified clade, entelegyne araneomorphs. Other clades are far less studied. Our study focused on haplogyne araneomorphs, which are remarkable for their unusual sex chromosome systems and for the co-evolution of sex chromosomes and nucleolus organizer regions (NORs); some haplogynes exhibit holokinetic chromosomes. To trace the karyotype evolution of haplogynes on the family level, we analysed the number and morphology of chromosomes, sex chromosomes, NORs, and meiosis in pholcids, which are among the most diverse haplogyne families. The evolution of spider NORs is largely unknown. RESULTS: Our study is based on an extensive set of species representing all major pholcid clades. Pholcids exhibit a low 2n and predominance of biarmed chromosomes, which are typical haplogyne features. Sex chromosomes and NOR patterns of pholcids are diversified. We revealed six sex chromosome systems in pholcids (X0, XY, X1X20, X1X2X30, X1X2Y, and X1X2X3X4Y). The number of NOR loci ranges from one to nine. In some clades, NORs are also found on sex chromosomes. CONCLUSIONS: The evolution of cytogenetic characters was largely derived from character mapping on a recently published molecular phylogeny of the family. Based on an extensive set of species and mapping of their characters, numerous conclusions regarding the karyotype evolution of pholcids and spiders can be drawn. Our results suggest frequent autosome-autosome and autosome-sex chromosome rearrangements during pholcid evolution. Such events have previously been attributed to the reproductive isolation of species. The peculiar X1X2Y system is probably ancestral for haplogynes. Chromosomes of the X1X2Y system differ considerably in their pattern of evolution. In some pholcid clades, the X1X2Y system has transformed into the X1X20 or XY systems, and subsequently into the X0 system. The X1X2X30 system of Smeringopus pallidus probably arose from the X1X20 system by an X chromosome fission. The X1X2X3X4Y system of Kambiwa probably evolved from the X1X2Y system by integration of a chromosome pair. Nucleolus organizer regions have frequently expanded on sex chromosomes, most probably by ectopic recombination. Our data suggest the involvement of sex chromosome-linked NORs in achiasmatic pairing.
- Keywords
- Achiasmatic pairing, Diffuse stage, Entelegyne, Haplogyne, Inactivation, Rearrangement, Segregation, Y chromosome, rDNA,
- MeSH
- Karyotype MeSH
- Karyotyping MeSH
- Meiosis genetics MeSH
- Spiders * genetics MeSH
- Sex Chromosomes genetics MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Spiders are an intriguing model to analyse sex chromosome evolution because of their peculiar multiple X chromosome systems. Y chromosomes were considered rare in this group, arising after neo-sex chromosome formation by X chromosome-autosome rearrangements. However, recent findings suggest that Y chromosomes are more common in spiders than previously thought. Besides neo-sex chromosomes, they are also involved in the ancient X1X2Y system of haplogyne spiders, whose origin is unknown. Furthermore, spiders seem to exhibit obligatorily one or two pairs of cryptic homomorphic XY chromosomes (further cryptic sex chromosome pairs, CSCPs), which could represent the ancestral spider sex chromosomes. Here, we analyse the molecular differentiation of particular types of spider Y chromosomes in a representative set of ten species by comparative genomic hybridisation (CGH). We found a high Y chromosome differentiation in haplogyne species with X1X2Y system except for Loxosceles spp. CSCP chromosomes exhibited generally low differentiation. Possible mechanisms and factors behind the observed patterns are discussed. The presence of autosomal regions marked predominantly or exclusively with the male or female probe was also recorded. We attribute this pattern to intraspecific variability in the copy number and distribution of certain repetitive DNAs in spider genomes, pointing thus to the limits of CGH in this arachnid group. In addition, we confirmed nonrandom association of chromosomes belonging to particular CSCPs at spermatogonial mitosis and spermatocyte meiosis and their association with multiple Xs throughout meiosis. Taken together, our data suggest diverse evolutionary pathways of molecular differentiation in different types of spider Y chromosomes.
- Keywords
- Arthropoda, X1X20, X1X2Y, Y chromosome, achiasmatic pairing, in situ hybridisation, karyotype evolution, male-specific region, neo-sex chromosome, repetitive DNA,
- MeSH
- Biological Evolution * MeSH
- Genome * MeSH
- Karyotype MeSH
- Meiosis * MeSH
- Spiders genetics MeSH
- Sex Chromosomes genetics MeSH
- Sex Differentiation * MeSH
- Comparative Genomic Hybridization methods MeSH
- Animals MeSH
- Check Tag
- Male MeSH
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
The knowledge of cytogenetics in the harvestmen family Phalangiidae has been based on taxa from the Northern Hemisphere. We performed cytogenetic analysis on Guruia africana (Karsch, 1878) (2n=24) and four species of the genus Rhampsinitus Simon, 1879 (2n=24, 26, 34) from South Africa. Fluorescence in situ hybridization with an 18S rDNA probe was used to analyze the number and the distribution of this cluster in the family Phalangiidae for the first time. The results support the cytogenetic characteristics typical for the majority of harvestmen taxa, i.e. the predominance of small biarmed chromosomes and the absence of morphologically well-differentiated sex chromosomes as an ancestral state. We identified the number of 18S rDNA sites ranging from two in R. qachasneki Kauri, 1962 to seven in one population of R. leighi Pocock, 1903. Moreover, we found differences in the number and localization of 18S rDNA sites in R. leighi between populations from two localities and between sexes of R. capensis (Loman, 1898). The heterozygous states of the 18S rDNA sites in these species may indicate the presence of XX/XY and ZZ/ZW sex chromosomes, and the possible existence of these systems in harvestmen is discussed. The variability of the 18S rDNA sites indicates intensive chromosomal changes during the differentiation of the karyotypes, which is in contrast to the usual uniformity in chromosomal morphology known from harvestmen so far.
- Keywords
- 18S rDNA, FISH, Karyotype, meiosis, sex chromosomes,
- Publication type
- Journal Article MeSH
Most spiders exhibit a multiple sex chromosome system, X(1)X(2)0, whose origin has not been satisfactorily explained. Examination of the sex chromosome systems in the spider genus Malthonica (Agelenidae) revealed considerable diversity in sex chromosome constitution within this group. Besides modes X(1)X(2)0 (M. silvestris) and X(1)X(2)X(3)0 (M. campestris), a neo-X(1)X(2)X(3)X(4)X(5)Y system in M. ferruginea was found. Ultrastructural analysis of spread pachytene spermatocytes revealed that the X(1)X(2)0 and X(1)X(2)X(3)0 systems include a pair of homomorphic sex chromosomes. Multiple X chromosomes and the pair exhibit an end-to-end pairing, being connected by attachment plaques. The X(1)X(2)X(3)X(4)X(5)Y system of M. ferruginea arose by rearrangement between the homomorphic sex chromosome pair and an autosome. Multiple X chromosomes and the sex chromosome pair do not differ from autosomes in a pattern of constitutive heterochromatin. Ultrastructural data on sex chromosome pairing in other spiders indicate that the homomorphic sex chromosome pair forms an integral part of the spider sex chromosome systems. It is suggested that this pair represents ancestral sex chromosomes of spiders, which generated multiple X chromosomes by non-disjunctions. Structural differentiation of newly formed X chromosomes has been facilitated by heterochromatinization of sex chromosome bivalents observed in prophase I of spider females.
- MeSH
- Biological Evolution * MeSH
- Meiosis physiology MeSH
- Chromosome Pairing MeSH
- Spiders classification genetics MeSH
- Sex Chromosomes genetics ultrastructure MeSH
- Chromosome Banding MeSH
- Microscopy, Electron, Transmission MeSH
- Animals MeSH
- Check Tag
- Male MeSH
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Concepts of spider karyotype evolution are based mostly on advanced and most diversified clade, the entelegyne lineage of araneomorph spiders. Hence the typical spider karyotype is supposed to consist exclusively of acrocentric chromosomes including the multiple X chromosomes. However, our data show considerable diversity of chromosome morphology and sex chromosome systems in basal clades of araneomorphs. Karyotypes of basal araneomorphs consist of holocentric (superfamily Dysderoidea) or normal chromosomes with localized centromere. In males of basal araneomorphs the prophase of first meiotic division includes a long diffuse stage. Multiple X chromosomes are less common in basal clades. The sex chromosome system of many families includes a Y chromosome or nucleolus organizer region that occurs rarely in the entelegyne spiders. A derived X(1)X(2)Y system with an achiasmatic sex-chromosome pairing during meiosis was found in the families Drymusidae, Hypochilidae, Filistatidae, Sicariidae, and Pholcidae. This suggests a monophyletic origin of the families. In some lineages the X(1)X(2)Y system converted into an X0 system, as found in some pholcids, or into an XY system, which is typical for the family Diguetidae. The remarkable karyotype and sex chromosome system diversity allows us to distinguish four evolutionary lineages of basal araneomorphs and hypothesize about the ancestral karyotype of araneomorphs.
- MeSH
- Biological Evolution MeSH
- Chromosomes genetics ultrastructure MeSH
- Karyotyping MeSH
- Meiosis MeSH
- Metaphase MeSH
- Spiders genetics MeSH
- Sex Chromosomes genetics ultrastructure MeSH
- Animals MeSH
- Check Tag
- Male MeSH
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
