Evolution of karyotype, sex chromosomes, and meiosis in mygalomorph spiders (Araneae: Mygalomorphae)

Abstract

Spider diversity is partitioned into three primary clades, namely Mesothelae, Mygalomorphae, and Araneomorphae. Mygalomorph cytogenetics is largely unknown. Our study revealed a remarkable karyotype diversity of mygalomorphs. Unlike araneomorphs, they show no general trend towards a decrease of 2n, as the chromosome number was reduced in some lineages and increased in others. A biarmed karyotype is a symplesiomorphy of mygalomorphs and araneomorphs. Male meiosis of some mygalomorphs is achiasmatic, or includes the diffuse stage. The sex chromosome system X1X20, which is supposedly ancestral in spiders, is uncommon in mygalomorphs. Many mygalomorphs exhibit more than two (and up to 13) X chromosomes in males. The evolution of X chromosomes proceeded via the duplication of chromosomes, fissions, X–X, and X‐autosome fusions. Spiders also exhibit a homomorphic sex chromosome pair. In the germline of mygalomorph males these chromosomes are often deactivated; their deactivation and pairing is initiated already at spermatogonia. Remarkably, pairing of sex chromosomes in mygalomorph females is also initiated at gonial cells. Some mygalomorphs have two sex chromosome pairs. The second pair presumably arose in early‐diverging mygalomorphs, probably via genome duplication. The unique behaviour of spider sex chromosomes in the germline may promote meiotic pairing of homologous sex chromosomes and structural differentiation of their duplicates, as well as the establishment of polyploid genomes. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 377–408.

Fissions, fusions, and translocations shaped the karyotype and multiple sex chromosome constitution of the northeast-Asian wood white butterfly,Leptidea amurensis

“…By contrast, a neo‐X 1 X 2 X 3 X 4 X 5 Y system in the spider Malthonica ferruginea probably evolved from an ancestral X 1 X 2 X 3 0 system, which included an additional pair of homomorphic proto‐sex chromosomes, by Robertsonian fusion between the proto‐Y chromosome and an autosome (Král, ). Moreover, some mygalomorph spiders exhibit up to 13 X chromosomes in males; the X‐multiples originated as a result of different chromosomal rearrangements, including duplications, fissions, and X–X and X–autosome fusions (Král et al ., ). The evolutionary significance of these types of complex multiple sex chromosome systems, including those recently described in three Leptidea butterfly species (Šíchová et al ., ), is poorly understood and deserves our full attention.…”

Cytogenetic analysis of five Ctenidae species (Araneae): detection of heterochromatin and 18S rDNA sites

“…However, molecular cytogenetic studies are scarce in spiders. There have been only five studies about distribution of some sequences using fluorescence in situ hybridization (FISH): location of 18S rDNA sites in Wadicosa fidelis (O. Pickard-Cambridge, 1872) (Lycosidae) (Forman et al 2013) and Brachypelma albopilosum Valerio, 1980 (Theraphosidae) (Král et al 2013); 5S rDNA sites in Oxyopes sertatus L. Koch, 1878 (Oxyopidae) (Suzuki and Kubota 2011); mapping of silk genes in Latrodectus hesperus Chamberlin & Ivie, 1935 and Latrodectus geometricus C. L. Koch, 1841 (Theridiidae) (Zhao et al 2010); and ocurrence of telomeric repeats in Brachypelma albopilosa Valerio, 1980 (Vítková et al 2005). …”

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

“…Rhampsinitus has a terminal position of 18S rDNA clusters, similarly to basal harvestmen of the suborder Cyphophthalmi (Svojanovská et al 2016), and other arachnid groups such as spiders (e.g. Král et al 2013), amblypygids (Paula-Neto et al 2013), and South American scorpions (e.g. Mattos et al 2014).…”