Jiří Král (1), Alexandr Sember (1, 2), Tereza Kořínková (1), K. Divišová (1), Azucena C. Reyes Lerma (1), Ivalú M. Ávila Herrera (1), Martin Forman (1), José G. Palacios Vargas (3), Magda Zrzavá (4, 5), Petr Nguyen (4, 5), Paula Cushing (6), Alexander V. Gromov (7) & Tharina L. Bird (8)
(1) Department of Genetics and Microbiology, Faculty of Science, Charles University, Prague 2, Czech Republic (2) Institute of Animal Physiology and Genetics, Academy of Sciences of the Czech Republic, Liběchov, Czech Republic (3) Department of Ecology and Natural Resources, Faculty of Science, National Autonomous University of Mexico, Mexico City, Mexico (4) Department of Molecular Biology and Genetics, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic (5) Institute of Entomology, Biology Centre, Academy of Sciences of the Czech Republic, České Budějovice, Czech Republic (6) Department of Zoology, Denver Museum of Nature and Science, Denver, CO, USA (7) Bingen am Rhein, Germany (8) Department of Biology and Biotechnological Sciences, Botswana International University of Science and Technology (BIUST), Palapye, Botswana
Arachnids are a highly diverse arthropod group, yet the organization and evolution of their genomes remain poorly understood. We aimed to reconstruct the karyotype evolution of tetrapulmonate arachnids, a major clade comprising Araneae (spiders), Amblypygi, Thelyphonida, and Schizomida. We performed a detailed cytogenetic analysis of the non-spider tetrapulmonate orders, plus two additional orders with putative close phylogenetic affinities to tetrapulmonates, namely the Ricinulei and Solifugae. Cytogenetics of these five orders is virtually unknown. Our study in combination with existing information indicates that ancestral arachnids had a low to average 2n, one pair of nucleolar organizer regions (NORs), low levels of heterochromatin and recombinations, and no heteromorphic gonosomes. Our results further indicate that the karyotypes of amblypygids, thelyphonids, schizomids, and solifuges diversified via centric fusions, pericentric inversions, and changes of NOR pattern and, in solifuges, also via tandem fusions. Although amblypygids and thelyphonids have a much lower species diversity than spiders, they possess a considerable karyotype differentiation. Some solifuges display an enormous expansion of heterochromatin and NOR number. Most non-spider tetrapulmonates differ from spiders by the absence of morphologically differentiated sex chromosomes. We hypothesize that the ancestor of amblypygids, thelyphonids, and spiders exhibited a homomorphic XY system, and that telomere heterochromatin and NORs were involved in the origin and evolution of amblypygid sex chromosomes. Our results do not support relationship of pseudoscorpions and solifuges. On the contrary, they support the Cephalosomata clade (comprising acariforms, palpigrades, and solifuges) and a genome duplication in the spider ancestors. This study was funded by Czech Science Foundation (16-10298S), Grant Agency of the Charles University (SVV-260314), National Science Foundation (DEB 0640245), and Chilean National Commission for Scientific and Technological Research (CONICYT).
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Jiří Král, Alexandr Sember, Tereza Kořínková, K. Divišová, Azucena C. Reyes Lerma, Ivalú M. Ávila Herrera, Martin Forman, José G. Palacios Vargas, Magda Zrzavá, Petr Nguyen, Paula Cushing, Alexander V. Gromov & Tharina L. Bird