Karyotype analysis and achiasmatic meiosis in pseudoscorpions of the family Chthoniidae (Arachnida: Pseudoscorpiones)

Abstract

Karyotypes of pseudoscorpions (Arachnida, Pseudoscorpiones) are largely unknown. Here we describe for the first time karyotypes of the suborder Epiocheirata, represented by 9 European species of two genera of Chthoniidae, Chthonius and Mundochthonius. Diploid chromosome numbers of males range from 21 to 37. Karyotypes of both genera differ substantially. Acrocentric chromosomes predominate in karyotypes of the genus Chthonius, whereas M. styriacus exhibits a predominance of metacentric chromosomes. These differences suggest that the two genera belong probably to distant branches of the family Chthoniidae. It is proposed that karyotype evolution of the genus Chthonius was characterised by a reduction of chromosome numbers by tandem and centric fusions as well as gradual conversion of acrocentric chromosomes to biarmed ones, mostly by pericentric inversions. A tendency towards reduced chromosome numbers is evident in the subgenus Ephippiochthonius. All species display X0 sex chromosome system that is probably ancestral in pseudoscorpions. The X chromosome exhibits conservative morphology. It is metacentric in all species examined, and in the majority of them, a subterminal secondary constriction was found at one of its arms. In contrast to chthoniids, secondary constriction was not reported on sex chromosomes of other pseudoscorpions. Analysis of prophase I chromosomes in males revealed an achiasmatic mode of meiosis. Findings of the achiasmatic meiosis in both genera, Chthonius and Mundochthonius, indicate that this mode of meiosis might be characteristic of the family Chthoniidae. Amongst arachnids, achiasmatic meiosis has only been described in some scorpions, acariform mites, and spiders.

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

“…Until now, the lack of recombination in male meiosis seems to be exclusive for Scorpiones species (Schneider et al, 2009a,b); in other groups, the chromosome association lacking chiasma occurs sporadically, e.g., in certain families of Araneae and Pseudoscorpiones (Rodríguez-Gil et al, 2002;Štáhlavský and Král, 2004). The sporadic occurrence of an achiasmate mode of meiosis in some arachnid orders indicates that the absence of recombination certainly has a secondary origin for these species.…”

The First Cytogenetic Characterization of Atemnids: Pseudoscorpions with the Highest Chromosome Numbers (Arachnida: Pseudoscorpiones)

“…Chromosome preparations were made following the spreading technique of Traut [1976], modified for pseudoscorpions by Šťáhlavský and Král [2004]. Briefly, the dissected gonads were placed in a hypotonic solution (0.075 M KCl) for 15 min and then fixed in a mixture of glacial acetic acid and methanol (1: 3) for at least 20 min.…”

“…Karyotypes of pseudoscorpions are significant for the considerable diversity in number and morphology of the autosomal pairs. Morphologically similar species often differ regarding their karyotype, as found in the genera Roncus [Troiano, 1990[Troiano, , 1997Zaragoza and Šťáhlavský, 2008] and Chthonius [Šťáhlavský and Král, 2004]. Therefore, detailed cytogenetic data may provide important information to help resolving taxonomic problems, and have the potential to reveal cryptic species.…”

“…The majority of pseudoscorpions examined so far (90%) belong to only 4 families, namely Chernetidae, Chthoniidae, Neobisiidae, and Olpiidae [Šťáhlavský and Král, 2004;Šťáhlavský et al, 2006Zaragoza and Šťáhlavský, 2008]. The diploid chromosome numbers of pseudoscorpions range between 7 in males of Olpium turcicum and Indolpium sp.…”

Comparison of different cytogenetic methods and tissue suitability for the study of chromosomes in Cimex lectularius (Heteroptera, Cimicidae)

“…Recently, this method has been used more frequently not only for study of chromosomes of various insect taxa , van't Hof et al 2011, Paladino et al 2013, Sadílek et al 2013, Chirino et al 2015 but also for all other main arthropod evolutionary lineages such as arachnids (e.g. Šťáhlavský and Král 2004, Forman et al 2013, Adilardi et al 2014, Sadílek et al 2015, myriapods (e.g. Green et al 2016), and crustaceans (e.g.…”