Abstract
Pseudoscorpions are found in almost all terrestrial habitats. However, their uniform appearance presents a challenge for morphology-based taxonomy, which may underestimate the diversity of this order. We performed cytogenetic analyses on 11 pseudoscorpion species of the genus Chthonius C. L. Koch, 1843 from the Alps, including three subgenera: Chthonius (Chthonius) C. L. Koch, 1843, Chthonius (Ephippiochthonius) Beier, 1930 and Chthonius (Globochthonius) Beier, 1931 inhabiting this region. The results show that the male diploid number of chromosomes ranges from 21–35. The sex chromosome system X0 has been detected in all male specimens. The X sex chromosome is always metacentric and represents the largest chromosome in the nucleus. Achiasmatic meiosis, already known from the family Chthoniidae, was further confirmed in males of Chthonius. C-banding corroborated the localization of constitutive heterochromatin in the centromere region, which corresponds to heteropycnotic knobs on the standard chromosome preparations. Morphological types and size differentiation of chromosomes in the karyotype suggest that the main chromosomal rearrangements in the evolution of Chthonius are centric or tandem fusions resulting in a decrease in the number of chromosomes. Pericentric inversions, inducing the change of acrocentric chromosomes into biarmed chromosomes, could also be expected. Variability in chromosome morphology and number was detected in several species: Chthonius (Chthonius) ischnocheles (Hermann, 1804), Chthonius (Chthonius) raridentatus, Chthonius (Chthonius) rhodochelatus Hadži, 1930, and Chthonius (Chthonius) tenuis L. Koch, 1873. We discuss the intraspecific variability within these species and the potential existence of cryptic species.
Highlights
Pseudoscorpions are the fourth most numerous order of the class Arachnida, comprising 3385 described species currently classified into 439 genera and 26 families (Harvey 2013)
11 species of Chthoniidae have been studied so far, eight of them belonging to the genus Chthonius from Romania, Czech Republic, and Greece (Šťáhlavský and Král 2004) (Table 1)
Achiasmatic meiosis has been confirmed in males of the genus Chthonius, which is probably characteristic for the entire family Chthoniidae (Šťáhlavský and Král 2004)
Summary
Pseudoscorpions are the fourth most numerous order of the class Arachnida, comprising 3385 described species currently classified into 439 genera and 26 families (Harvey 2013). Molecular techniques have further revealed the limitations of traditional morphology-based classification of pseudoscorpions. Despite the absence of molecular techniques in formal species delimitation in this group, independent lineages that may correspond to cryptic species have been detected in number of cases Wilcox et al 1997, Moulds et al 2007, Pfeiler et al 2009, van Heerden et al 2013, Harrison et al 2014) Another useful method for detecting unaccounted diversity is karyotype analysis. Significant interspecific differences in karyotypes may reveal distinct lineages constituting cryptic species in some morphologically challenging groups (e.g. Řezáč et al 2007, Lukhtanov et al 2015). The use of cytogenetic methods has enabled the detection of interspecific variability (Troiano 1990, Šťáhlavský et al 2006, 2013) and has led to the description of a new species (Zaragoza and Šťáhlavský 2008)
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