Evolution of the karyotype and sex chromosome systems in basal clades of araneomorph spiders (Araneae: Araneomorphae)

Abstract

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.

Cytogenetic characterization of ten araneomorph spiders (Araneae): Karyotypes and meiotic features

“…Loxosceles rufescens is an example that shows an X 1 X 2 Y sex chromosome system, with presence of an Y chromosome and biarmed chromosomes in a karyotype. My results are compatible with those of Král et al (2006) who also found 2n = 21, X 1 X 2 Y. However, the first investigations provided by Beçak & Beçak (1960) revealed 2n = 20.…”

Chromosomal characteristics of a Brazilian whip spider (Amblypygi) and evolutionary relationships with other arachnid orders

“…The number and location of NORs were only established, for example, in approximately 30 species of Araneae (Král et al, 2006;Král, 2007;Oliveira et al, 2007;Rodríguez-Gil et al, 2007;Araujo et al, 2008;Stávale et al, 2010Stávale et al, , 2011Dolejš et al, 2011;Král et al, 2011), 17 species of Scorpiones (Schneider et al, 2009a,b;Schneider and Cella, 2010), 3 species of Opiliones (Gorlov and Tsurusaki, 2000;Oliveira et al, 2006;Schneider et al, 2008;Mattos et al, 2013), and two species of Palpigradi (Král et al, 2008). In almost all these species, the NORs were only identified through the use of silver impregnation; however, in an overview of the NOR distribution in Coleoptera, Schneider et al (2007) showed that the results were usually coincident when the chromosomes were examined with both silver impregnation and FISH technique.…”

Development of male gametophyte of Larix leptolepis Gord. with emphasis on diffuse stage of meiosis

“…This stage has been described in male meiosis of many organisms (Moens 1964;Barry 1969;Nagl 1969;Sen 1969;Pogoslanz 1970;Klášterská and Natarajan 1974;Oud et al 1979;Cawood and Jones 1980;Cardoso et al 1986). Pre-diffuse diplotene is the transition from the early diplotene into the diffuse stage, during which the chromosomes despiralize and reorganize with the (Klášterská 1976;Seitz et al 1996;Cattani and Papeschi 2004;Král et al 2006). Post-diffuse diplotene is mainly characterized by recondensation of the homologous chromosomes to allow meiosis to enter the normal diplotene stage.…”