Introduction into karyotype evolution of pseudoscorpions
Šťáhlavský F.1,2, J. Král2, H. Henderickx3 & M.S. Harvey4
Department of Zoology, Faculty of Sciences, Charles University, Viničná 7, CZ-128 44 Prague 2, Czech
Republic. E-mail: stahlf@natur.cuni.cz
2
Laboratory of Arachnid Cytogenetics, Department of Genetics and Microbiology, Faculty of Sciences, Charles
University, Viničná 5, CZ-128 44 Prague 2, Czech Republic. E-mail: spider@natur.cuni.cz
3
Hemelrijkstraat 4, B-2400 Mol, Belgium. E-mail: hans.henderickx@pandora.be
4
Department of Terrestrial Invertebrates, Western Australian Museum, Perth, Western Australia 6000, Australia.
E-mail: mark.harvey@museum.wa.gov.au
1
Knowledge about the karyology of pseudoscorpions is still very limited in comparison with other
species-rich arachnid orders. Until the end of the last century, the karyotypes of only nine species
from three families had been described. During our current research, we have obtained results
(published or preliminary) in a further forty species belonging to ten families, namely Atemnidae,
Cheiridiidae, Cheliferidae, Chernetidae, Chthoniidae, Garypidae, Geogarypidae, Larcidae,
Olpiidae, and Neobisiidae. The results obtained suggests that the karyotypes of pseudoscorpions
consists of monocentric chromosomes; biarmed chromosomes predominate in the majority of
species. We have discovered various sex chromosome systems in pseudoscorpions, namely X0,
XY, and neo-sex chromosome systems. The X0 system is probably the ancestral mode because it
is most frequent mode in all families studied. In contrast to other families, males of chthoniids are
characterised by an achiasmatic type of meiosis. Pseudoscorpions display enormous interspecific
variation in karyotypes. In spite of this, our results allow us to hypothesise that evolution of many
groups has been accompanied by a reduction of the chromosome numbers. It is easy to observe
this trend, for example, in the genus Chthonius whose ancestral karyotype consists of acrocentric
chromosomes only. Reduction of chromosome numbers was characterised by tandem and centric
fusions as well as gradual conversion of acrocentric chromosomes to bi-armed ones, mostly by
pericentric inversions. A tendency towards reduced chromosome numbers is also obvious in
karyotype evolution of the genus Neobisium (Neobisiidae). Like some chthoniid lineages,
reduction of chromosome numbers took place via multiple fusions that led to conspicuous
"macrochromosomes". Great diversity in karyotypes appears to be useful for cytotaxonomic
studies as for example in the ongoing contemporary analysis of Neobisium carcinoides complex.
Therefore, it is obvious that karyological studies on pseudoscorpions can help to resolve
taxonomic problems and moreover, to construct hypotheses about the evolution within order.
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