Laboratory of Arachnid Cytogenetics
Assoc. Prof. RNDr. Jiří Král, Ph.D.
Phone: +420 221 951 737, +420 221 951 736
The Laboratory of Arachnid Cytogenetics is one of the few research groups specializing in the chromosomal research of arachnids. Arachnids are an extremely diversified arthropod clade including more than 100,000 extant species. Some arachnid groups (acari, spiders, scorpions) are very important from an economic or medical point of view. Although more chromosomal studies have been done in some species-rich arachnid orders, arachnid cytogenetics remains unsatisfactorily understood. In spite of that, the existing data indicate a considerable diversification of karyotypes during the evolution of the arachnid lineage. Some arachnids are potential model groups for the analysis of some intriguing fundamental questions of modern cytogenetics, e.g. the evolution of sex and holokinetic chromosomes, meiosis, parthenogenesis or the co-evolution of genome and sociality.
The main aim of our research group is to elucidate karyotype and sex chromosome evolution in arachnids. Sex chromosomes belong to fundamental themes of contemporary evolutionary genetics as they are involved in processes such as sex determination, sexual conflict or speciation. Spiders represent, among others, an interesting system for studying sex chromosomes because of the peculiar multiple X chromosome systems in their karyotypes. The most common spider sex chromosome system is designated as X1X20 (where “0” denotes the absence of the Y chromosome). This system is otherwise rare among organisms but is widespread among spiders and regarded as an ancestral spider trait. Notably, subsequent evolution leads to the multiplication of the X chromosome number. According to our data, sex chromosome systems of some spiders are among the most complex sex chromosome determinations found so far. They can be composed of up to 13 X chromosomes (Král et al., 2013). The origin of spider multiple X chromosome systems has not yet been resolved. Our data suggest that the sex chromosome determination of spiders is much more complex than previously thought, and that it includes one or even two specific sex chromosome pairs. Interestingly, chromosomes of these pairs lack morphological differentiation. Therefore, one can assume that these sex chromosome pairs only differentiate on a molecular level with one sex chromosome acting as a proto-X and the other one as a proto-Y. In some spiders, rearrangements between sex chromosomes and autosomes formed even more complicated sex chromosome determinations, for example the X1X2X3X4X5Y system in a common house spider Tegenaria ferruginea (Král, 2007). Altogether, spiders belong to the group with the most diversified sex chromosome systems. A detection of specific mechanisms responsible for unusual sex chromosome evolution in spiders is indisputably a promising research field.
Besides sex chromosomes, we focus on the evolution of holokinetic chromosomes, which are also found in some arachnids, namely dysderoid spiders, buthid scorpions, and some clades of acari. From an evolutionary point of view, holokinetic chromosomes are derived. They lack, for example, localised centromere and microtubules are attached to a major part of the chromosome surface facing the poles. Due to specific structural features, these chromosomes often show rapid accumulation of chromosomal rearrangements. According to our data, chromosomal rearrangements take part in speciation events in spiders of the Dysderidae family. Some dysderid genera belong to the most speciose of spider genera found so far. Therefore, cytogenetics is a powerful tool to distinguish closely related species of dysderids as well as to understand the origins of the biodiversity of these spiders (Řezáč et al. 2014).
Our other research topics also include the evolution of meiosis, polyploidy, and genome modifications linked with sociality. In addition to arachnids, we participate in cytogenetic research on other invertebrates (molluscans, crustaceans) and parasitic protists. Our laboratory is fully equipped for standard cytogenetics (the production of chromosome preparations, banding techniques) and various variants of fluorescence in situ hybridization (FISH). We also use methods of flow cytometry, transmission electron microscopy as well as bioinformatics and phylogenetic approaches. Specimens for study are obtained during expeditions, from specialists and from arachnid cultures at our Laboratory. We have organized or taken part in expeditions to Greece, the Middle East, South Africa, central Asia and Mexico. We participate in various domestic and foreign projects focused on the cytogenetics and biology of arachnids, including US National Science Foundation project "Global Survey and Inventory of Solifugae".