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Comparative analysis of spider genome sizes

Eva Líznarová, Stano Pekár & Petr Bureš

Department of Botany and Zoology, Faculty of Science, Masaryk University, Brno, Czech Republic

The genome size is one of the most fundamental genetic properties of living organisms. Genome size is defined as the total amount of DNA contained within haploid chromosome set. Important findings from the study of genome sizes are that the sizes vary dramatically among species and that this variation has no relationship to organismal complexity. It was found that haploid genome size is positively correlated with cell size, and negatively with cell division rate in a variety of taxa. The genome sizes of animal species vary more than 5000-fold, but both the evolutionary implications and the mechanisms responsible for the origin of this diversity remain unclear. Arthropods represent, by far, the dominant forms of multicellular life on the planet, yet the genome sizes of several groups (e.g. arachnids, myriapods) remain almost entirely unknown. Nevertheless, studies of genome size variation and its phenotypic impacts are not entirely lacking for invertebrates. In copepod crustaceans, for example, significant negative relationships have been reported between genome size and developmental rate. Positive associations between genome size and body size have been reported in flatworms, molluscs, copepod crustaceans, aphids and flies. Spiders represent a diverse group of animals, but to date there is just one study, where the genome sizes of about one hundred species out of more than 47 thousands described species were measured. We followed up in this research and we used flow cytometry to measure genome sizes of another 106 spider species from 26 families occurring in Europe. We found quite high variability in genome sizes among different spider families, the smallest genomes were found in the families Palpimanidae and Pholcidae, while the biggest genomes were found in the Oecobiidae and Segestriidae. Also within several families quite high variability in genome sizes was found. Within species, females always have bigger genome, which is given by unusual type of sex determination system X1X20 occurring in the majority of spider species.

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Eva Líznarová, Stano Pekár & Petr Bureš