Cytogenetics of entelegyne spiders (Arachnida, Araneae) from southern Africa

Taxonomic notes, distribution update and the first chromosomal analysis of Vectius niger (Simon, 1880) and Trochanteria gomezi Canals, 1933 (Araneae: Trochanteriidae)

Spiders of the family Trochanteriidae are characterized by the carapace being extremely flat, with a reflex border, medium posterior eyes flattened, laterigrade legs, the absence of claw tufts, anterior lateral spinnerets with an incomplete distal article, and an inflatable and epiginal plate formed by a divided plate. Two out of the six worldwide genera of Trocantheriids have species in the Brazilian areas: Trochanteria Karsch and Vectius Simon. Here we present the redescription of Vectius niger and morphological data of Trochanteria gomezi, with an expansion of the distribution of these species in the Neotropical region and unpublished chromosomal data of both species. Mitotic and meiotic cells of both T. gomezi and V. niger showed 2n=22 and 2n=24 telocentric chromosomes, with a sex chromosome system of the type X1X2 in males/X1X1X2X2 in females. The chromosomal data shown here matches those found in trochanteriids to date.

Chromosomal Study on Selected Small Araneomorph Spiders from Brazil, Including the First Records in Palpimanidae and Theridiosomatidae (Araneae, Araneomorphae)

Among the 50,474 spider species, only 849 have chromosomal data available in the literature. Fifty spider families remain unknown from a cytogenetic perspective. The aim of this study was to analyze chromosomally selected araneomorph spiders from Brazil, to contribute to the cytotaxonomy and chromosome evolution of this group. The karyotypes of 12 species belonging to families Corinnidae, Linyphiidae, Oonopidae, Palpimanidae, Theridiidae, Theridiosomatidae, Trachelidae, and Zodariidae were analyzed, including the first chromosomal record for the first two families. Specimens (with the abdomen content partially exposed by perforation) were subjected to colchicine, hypotonization, and fixation. In most cases, the total content of the abdomen was used to prepare slides by spreading of cell suspension and subsequent Giemsa staining. The results were as follows: Cinetomorpha simplex Simon, 1892 (Oonopidae) 2n♂ = 9, X0; Neotrops sp. and Neoxyphinus termitophilus (Oonopidae), 2n♂ = 7, X0; Otiothops birabeni (Palpimanidae); Agyneta sp. (Linyphiidae), 2n♂ = 24, X1X20; Coleosoma floridanum, Thymoites sp.1 and Thymoites sp.2 (Theridiidae), 2n♂ = 22, X1X20; Naatlo sp. (Theridiosomatidae), 2n♂ = 30, X1X20; Orthobula sp. (Trachelidae) 2n♂ = 21, X0; Falconina sp. (Corinnidae), 2n♂ = 28, X1X20; Epicratinus sp. (Zodariidae) 2n♂ = 42, X1X20. The chromosomal morphology was determined for all the samples except for Oonopidae. Most species exhibited telocentric chromosomes, with the exception of Palpimanidae and Theridiosomatidae. The main findings: 1) support an hypothesis on ancestral karyotype of Zodariidae and Oonopidae; 2) reveal a relatively high chromosome number in Palpimanidae that supports an idea on relatively high ancestral chromosome number (2n♂ = 42) of entelegyne spiders (Palpimanoidea is sister group of entelegyne spiders); 3) show that the karyotype found in Theridiosomatidae is exceptional within the Araneoidea.

Karyotype differentiation and male meiosis in European clades of the spider genus Pholcus (Araneae, Pholcidae)

Haplogyne araneomorphs are a diverse spider clade. Their karyotypes are usually predominated by biarmed (i.e., metacentric and submetacentric) chromosomes and have a specific sex chromosome system, X₁X₂Y. These features are probably ancestral for haplogynes. Nucleolus organizer regions (NORs) spread frequently from autosomes to sex chromosomes in these spiders. This study focuses on pholcids (Pholcidae), a highly diverse haplogyne family. Despite considerable recent progress in pholcid cytogenetics, knowledge on many clades remains insufficient including the most species-rich pholcid genus, Pholcus Walckenaer, 1805. To characterize the karyotype differentiation of Pholcus in Europe, we compared karyotypes, sex chromosomes, NORs, and male meiosis of seven species [P.alticeps Spassky, 1932; P.creticus Senglet, 1971; P.dentatus Wunderlich, 1995; P.fuerteventurensis Wunderlich, 1992; P.phalangioides (Fuesslin, 1775); P.opilionoides (Schrank, 1781); P.silvai Wunderlich, 1995] representing the dominant species groups in this region. The species studied show several features ancestral for Pholcus, namely the 2n♂ = 25, the X₁X₂Y system, and a karyotype predominated by biarmed chromosomes. Most taxa have a large acrocentric NOR-bearing pair, which evolved from a biarmed pair by a pericentric inversion. In some lineages, the acrocentric pair reverted to biarmed. Closely related species often differ in the morphology of some chromosome pairs, probably resulting from pericentric inversions and/or translocations. Such rearrangements have been implicated in the formation of reproductive barriers. While the X₁ and Y chromosomes retain their ancestral metacentric morphology, the X₂ chromosome shows a derived (acrocentric or subtelocentric) morphology. Pairing of this element is usually modified during male meiosis. NOR patterns are very diverse. The ancestral karyotype of Pholcus contained five or six terminal NORs including three X chromosome-linked loci. The number of NORs has been frequently reduced during evolution. In the Macaronesian clade, there is only a single NOR-bearing pair. Sex chromosome-linked NORs are lost in Madeiran species and in P.creticus. Our study revealed two cytotypes in the synanthropic species P.phalangioides (Madeiran and Czech), which differ by their NOR pattern and chromosome morphology. In the Czech cytotype, the large acrocentric pair was transformed into a biarmed pair by pericentric inversion.

Insights into the Karyotype Evolution of Charinidae, the Early-Diverging Clade of Whip Spiders (Arachnida: Amblypygi)

Whip spiders (Amblypygi) represent an ancient order of tetrapulmonate arachnids with a low diversity. Their cytogenetic data are confined to only a few reports. Here, we analyzed the family Charinidae, a lineage almost at the base of the amblypygids, providing an insight into the ancestral traits and basic trajectories of amblypygid karyotype evolution. We performed Giemsa staining, selected banding techniques, and detected 18S ribosomal DNA and telomeric repeats by fluorescence in situ hybridization in four Charinus and five Sarax species. Both genera exhibit a wide range of diploid chromosome numbers (2n = 42-76 and 22-74 for Charinus and Sarax, respectively). The 2n reduction was accompanied by an increase of proportion of biarmed elements. We further revealed a single NOR site (probably an ancestral condition for charinids), the presence of a (TTAGG)n telomeric motif localized mostly at the chromosome ends, and an absence of heteromorphic sex chromosomes. Our data collectively suggest a high pace of karyotype repatterning in amblypygids, with probably a high ancestral 2n and its subsequent gradual reduction by fusions, and the action of pericentric inversions, similarly to what has been proposed for neoamblypygids. The possible contribution of fissions to charinid karyotype repatterning, however, cannot be fully ruled out.

First chromosomal analysis in Deinopidae (Araneae) reveals Sex Chromosome System X1X2X3X4, B chromosomes and polymorphism for centric fusion

Here we present the first cytogentic study concerning Deinopidae and their controversial phylogenetic position. This study karyologically analyzed one population of Deinopis biaculeata Simon, 1906 and five populations of Deinopis plurituberculata Mello-Leitão, 1925. The majority of specimens of D. plurituberculata exhibited 2n♂ = 40 and 2n♀ = 44 telocentric chromosomes (however some of them showed B chromosomes, belongs to Aquidauana and Botucatu population). The Deinopis biaculeata and D. plurituberculata meiosis of males showed 18 autosomal bivalents + X₁X₂X₃X₄, n = 22 and n = 18, a rare sex chromosome system (SCS) in spiders. Some individuals of D. plurituberculata from the Campo Grande population exhibited 2n♂ = 39 and 2n♀ = 43, with a metacentric chromosome (heterozygotes for centric fusion). The D. plurituberculata males with the rearrangement exhibit diplotenes with 16 autosomal bivalents + 1 autosomal trivalent + X₁X₂X₃X₄ and metaphases II with n = 22 (18 telocentric autosomes + X₁X₂X₃X₄), n = 21 (16 telocentric autosomes + a metacentric autosome + X₁X₂X₃X₄), n = 18 (18 telocentric autosomes) and n = 17 (16 telocentric autosomes + a metacentric autosome). The Ag-NORs (silver impregnation) are terminally located in a pair, coinciding with secondary constriction, which is the most common configuration for Araneae. The relatively high diploid number in Deinopis corroborates phylogenies that place it in a basal position among Entelegynes, in the UDOH grade (Uloboridae, Deinopidae, Oecobiidae and Hersiliidae). Centric fusion in only one population of D. plurituberculata suggests low dispersion capacity of this species and an absence of homozygotes for fusion suggests their low viability or a need to increase the population sampling of D. plurituberculata exhibiting the rearrangement. B chromosomes were detected in D. plurituberculata, with interpopulacional, intrapopulacional and intraindividual numerical variation, with cells presenting 0 - 3 and 0 - 6 B chromosomes in populations of Aquidauana and Botucatu, respectively.

Evolutionary dynamics of rDNA clusters on chromosomes of buthid scorpions (Chelicerata: Arachnida)

We examined the distribution of genes for major ribosomal RNAs (rDNA) on holokinetic chromosomes of 74 species belonging to 19 genera of scorpions from the family Buthidae using fluorescence in situ hybridization (FISH). Our analysis revealed differences between the two main evolutionary lineages within the family. The genera belonging to the ‘Buthus group’, with a proposed Laurasian origin, possess one pair of rDNA mainly in an interstitial position, with the only exceptions being the terminal location found in some Hottentotta and Buthacus species, possibly as a result of chromosome fissions. All the remaining buthid ‘groups’ possess rDNA found strictly in a terminal position. However, the number of signals may increase from an ancestral state of one pair of rDNA loci to up to seven signals in Reddyanus ceylonensis Kovařík et al., 2016. Despite the differences in evolutionary dynamics of the rDNA clusters between the ‘Buthus group’ and other lineages investigated, we found a high incidence of reciprocal translocations and presence of multivalent associations during meiosis in the majority of the genera studied. These phenomena seem to be typical for the whole family Buthidae.