Sex Chromosome Pairing and Extensive NOR Polymorphism in <b><i>Wadicosa fidelis</i></b> (Araneae: Lycosidae)

Abstract

In terms of cytogenetics, entelegyne araneomorphs are the best studied clade of spiders. The typical karyotype of entelegyne males consists of acrocentric chromosomes, including 2 non-homologous X chromosomes. The present study is focused on the karyotype, nucleolus organising regions (NORs) and sex chromosome behaviour during meiosis of the entelegyne Wadicosa fidelis (Lycosidae). Preparations stained by Giemsa were used to study karyotype and meiosis. NORs were visualised by silver staining and fluorescence in situ hybridisation with 18S rDNA probe. The male karyotype consists of 28 acrocentric elements, including 2 X chromosomes. In contrast to the majority of other spiders, the male sex chromosomes pair during the major part of meiosis. Following an initial period of parallel pairing, the attachment of male sex chromosomes is restricted to centromeric areas and continues until metaphase II. Our study revealed an enormous number of NORs in the population from Galilee and indicates a considerable variability of NOR numbers in this population. The distal regions of 9 or 10 autosomal pairs contain NORs. The obtained data indicate the rapid spread of NORs in the karyotype of W. fidelis, which was presumably caused by ectopic recombinations and subsequent hybridisations of individuals with different NOR genotypes that produced heterozygotes.

Karyotype Evolution in Harvestmen of the Suborder Cyphophthalmi (Opiliones)

“…Clusters of rDNA have been mapped only in ∼ 30 species of spiders [Král et al, , 2011Král, 2007;Oliveira et al, 2007;Rodríguez-Gil et al, 2007;Araujo et al, 2008;Stávale et al, 2010Stávale et al, , 2011Dolejš et al, 2011], 17 species of scorpions [Schneider et al, 2009a, b;Schneider and Cella, 2010;Mattos et al, 2013], 1 species of Amblypygi [Paula-Neto et al, 2013], and 1 species of Palpigradi [Král et al, 2008]. However, in these studies, NORs were mostly visualized by silver staining, and FISH detection using specific probes for rDNA clusters has only been done in a few recent studies Forman et al, 2013;Paula-Neto et al, 2013;Adilardi et al, 2014Adilardi et al, , 2015Mattos et al, 2014;Sadílek et al, 2015]. It seems to be clear that the majority of arachnids possess 1 pair of rDNA loci mostly in a terminal position.…”

“…The 18S rDNA probe for FISH was obtained from the spider Dysdera erythrina (Walckenaer, 1802) (Dysderidae), as described by Forman et al [2013]. A partial sequence of the 18S rRNA gene was amplified by polymerase chain reaction and labeled with biotin-14-dUTP by nick translation using a nick translation kit (Abbott Molecular).…”

Repetitive DNA chromosomal organization in the cricket Cycloptiloides americanus: a case of the unusual X1X20 sex chromosome system in Orthoptera

“…The submetacentric X 2 that was described by Mesa et al (2002) corresponds to autosomal pair 4, which occurs invariably in two copies in both sexes and is easily recognized in some cells due to the occurrence of less-condensed chromatin in the middle of the long arm. The X 1 X 2 0♂/X 1 X 1 X 2 X 2 ♀ sex-determining system that has been described in the cricket C. americanus is a rare case of this type that has been observed in Orthoptera, but it is apparently common in some other invertebrates, such as spiders (White 1973;Maddison and Leduc-Robert 2013;Forman et al 2013;Zefa et al 2014) and some species of Heteroptera (Ueshima 1979;Kusnetzova 1988); Homoptera (Morgan 1915;White 1940) and Nematoda (Walton 1924;White 1940), and it is uncommon in eukaryotes as a whole. Concerning the origin of this system, in spiders, for example, the X 1 X 2 0 sex-determining system is considered a plesiomorphic feature, and various hypotheses for its origin have been raised, including the duplication of the original X chromosome, centric fragmentation, fission and the translocation of an X segment to a centric fragment of a supernumerary chromosome, among others (reviewed by Araujo et al 2012).…”

Molecular technique reveals high variability of 18S rDNA distribution in harvestmen (Opiliones, Phalangiidae) from South Africa

“…The FISH protocol was performed following Forman et al (2013). Briefly, chromosome preparations were treated with RNase A (200 µg/ml in 2× SSC) for 60 min and then washed twice in 2× SSC for 5 min.…”