Conventional and ultrastructural analyses of the chromosomes ofDiscocyrtus pectinifemur(Opiliones, Laniatores, Gonyleptidae)

Abstract

Among the Opiliones, species of the suborders Cyphophthalmi, Eupnoi, Dyspnoi and Laniatores have shown very diverse diploid chromosome numbers. However, only certain Eupnoi species exhibit XY⁄XX and ZZ⁄ZW sex chromosome systems. Considering the scarcity of karyotypical information and the absence of structurally identifiable sex chromosomes in the suborder Laniatores, we decided to analyse the chromosomes and bivalents of Discocyrtus pectinifemur (Gonyleptidae) to identify possible sex differences. Testicular cells examined under light microscopy showed a high diploid number, 2n = 88, meta⁄submetacentric chromosome morphology and a nucleolar organizer region on pair 35. Prophase I microspreading observed in transmission electron microscopy exhibited 44 synaptonemal complexes with similar electron density and thickness. The total and regular synapsis between the chromosomes of the bivalents was also noted in pachytene nuclei. Male mitotic and meiotic chromosomes revealed no distinct characteristic that could be related to the occurrence of heteromorphic sex chromosomes. Evolutionary trends of chromosome differentiation in the four suborders of Opiliones are discussed here.

Chromosomal characteristics of a Brazilian whip spider (Amblypygi) and evolutionary relationships with other arachnid orders

“…The absence of morphologically differentiated sex chromosomes (i.e., homomorphic) is not an exclusive feature of the Amblypygi species investigated here, but it has also been recorded in all scorpions and in most harvestmen cytogenetically characterized (Schneider et al, 2008(Schneider et al, , 2009a. Král et al (2008) demonstrated the absence of morphologically differentiated sex chromosomes in Palpigradi species, an arachnid order with numerous primitive characters, and proposed that this condition could constitute an ancestral state for Arachnida.…”

“…The number and location of NORs were only established, for example, in approximately 30 species of Araneae (Král et al, 2006;Král, 2007;Oliveira et al, 2007;Rodríguez-Gil et al, 2007;Araujo et al, 2008;Stávale et al, 2010Stávale et al, , 2011Dolejš et al, 2011;Král et al, 2011), 17 species of Scorpiones (Schneider et al, 2009a,b;Schneider and Cella, 2010), 3 species of Opiliones (Gorlov and Tsurusaki, 2000;Oliveira et al, 2006;Schneider et al, 2008;Mattos et al, 2013), and two species of Palpigradi (Král et al, 2008). In almost all these species, the NORs were only identified through the use of silver impregnation; however, in an overview of the NOR distribution in Coleoptera, Schneider et al (2007) showed that the results were usually coincident when the chromosomes were examined with both silver impregnation and FISH technique.…”

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

“…Notably, data from both silver staining [e.g. Gunn and Hilburn, 1989;Král et al, 2008;Schneider et al, 2008] and FISH [Hill et al, 2009;Meyer et al, 2010;Schneider and Cella, 2010] indicate that one NOR pair is the most common pattern in arachnids. Therefore, one NOR pair could be the ancestral characteristic of this class.…”

Karyotype Evolution in Harvestmen of the Suborder Cyphophthalmi (Opiliones)

“…In harvestmen, the number and the distribution of rDNA loci have up to now only been examined by means of silver staining of nucleolar argyrophilic proteins, hence detecting only transcriptionally active rDNA clusters [Gorlov and Tsurusaki, 2000b;Oliveira et al, 2006;Schneider et al, 2008]. Only a single rDNA cluster was visualized in a diploid set of Psathyropus tenuipes (L. Koch, 1878) (Sclerosomatidae) [Gorlov and Tsurusaki, 2000b] and Dyscocyrtus pectinifemur (Mello-Leitão, 1937) (Gonyleptidae) [Schneider et al, 2008], while 1 pair of rDNA loci was noted in Goniosoma spelaeum (Mello-Leitão, 1932) [Oliveira et al, 2006]. In other arachnid orders, the data on the number and the position of rDNA are still fragmentary, too.…”