Cytogenetical characterization of six orb-weaver species and review of cytogenetical data for Araneidae

Abstract

The family Araneidae is the third largest among spiders and the third most studied from a cytogenetical point of view. In spite of this, only 2% of all araneids have been karyotyped. The majority of araneids analyzed possess 2n = 24 chromosomes in males; however, the study of additional species could reveal unusual karyotype characteristics. Thus, the aim of this work is to analyze chromosomally, for the first time, six species belonging to three araneid genera from Brazil. The specimens of Alpaida leucogramnui (White 1841), Alpaida tnmeata (Keyserling 1865), Alpaida veniliae (Keyserling 1865), Parawixia kochi (Taezanowski 1873), ParawLxki velutina (Taezanowski 1878) and Wagneriana sp. were collected in Barque Nacional de Ilha Grande and in the municipality of Rio Claro. The gonads were treated with colchicine and hypotonic solution before fixation with Carnoy I solution. The results were 2nS = 24 (IIII+XiXt) in A. leucogramnui and P. velutina, and 2nS = 22 (10n+XiX2) in A. truncata, A. veniliae, P. kochi and Wagneriana sp. When the chromosomal morphologies were established, we observed telocentric chromosomes in all specimens save one female specimen of P. velutina. The univalent sex chromosomes were easily recognized on diplotenes. The unpaired metacentric element found in one female specimen of P. velutina with 2n = 25 probably arises by centric fusion/fission. Araneidae is a megadiverse family composed of -3000 species distributed mainly in the tropics; thus the analysis of more species may provide new insights about orb-weaver chromosome evolution.

Chromosomal similarities between Nephilidae and Tetragnathidae indicate unique evolutionary traits among Araneoidea

“…Those regions were not described on sex chromosomes in any of the 14 species of Araneidae, Linyphiidae, Nesticidae and Theridiidae that were cytogenetically analyzed with similar procedures to that employed here (Matsumoto 1977;Tugmon et al 1990;Gunnarsson & Andersson 1992;Araujo et al 2010Araujo et al , 2011Stávale et al 2010;Zhao et al 2010). The importance of sharing secondary constrictions on sex chromosomes is still more relevant when we notice that these regions are also related to NORs, as revealed by silver impregnation in the species analyzed here and in the tetragnathid spiders examined by Král et al (2011).…”

“…Given that the chromosomal morphology, excluding some very few cases, is also monoarmed in araneoid spiders (Araujo et al 2015), tandem fusions and/or centric fusions followed by pericentric inversions seem to be the rearrangements involved in these reductions of diploid number. Centric fusion is a well-documented mechanism that commonly underlies the karyotype evolution of spiders, as registered in some araneids with 2n♂ = 14 (10 biarmed and four monoarmed chromosomes), a karyotype that certainly evolved from the 2n♂ = 24 (all monoarmed chromosomes) (Hackman 1948;Suzuki 1951;Amalin et al 1993), and in one araneid specimen of Parawixia velutina (Taczanowski, 1873), which was heterozygous for a centric fusion, presenting an odd metacentric element in the karyotype (Araujo et al 2011). Evidence of several pericentric inversions were encountered by Stávale et al (2010) in Argyrodes elevatus Taczanowski, 1873 (Theridiidae), in which all 20 autosomal chromosomes are biarmed, contrasting with the majority of theridiid species, in which all 20 autosomes are monoarmed (Araujo et al 2015).…”

Chromosome-level reference genome of the European wasp spiderArgiope bruennichi: a resource for studies on range expansion and evolutionary adaptation

“…Genome assembly statistics were calculated using QUAST v. 5.0.2 (QUAST, RRID:SCR_001228 ) [ 60 ] applying default parameters, except setting the minimum contig length (–min-contig parameter) to 0. Previous studies have inferred the chromosome number of A. bruennichi to be 13, indicating that our genome assembly achieved full-chromosome level [ 61 , 62 ]. As an additional assessment of assembly quality, we ran the K-mer Analysis Toolkit v. 2.4.2 (KAT, RRID:SCR_016741 ) [ 63 ] “comp" tool, comparing the k -mer content in the Illumina sequencing data to the k -mer content in the final assembly.…”

Studies on chromosomal characteristics of Ctenus indicus (Gravely 1931) (Araneae: Ctenidae)

“…Another diagnostic cytogenetic feature that frequently encountered during the course of chromosomal studies of spiders had been their prevalence towards inclusive nature of multiple sex chromosome polymorphisms [4]. Earlier studies have documented their phylogenies eliciting evolutionary trend following XX-XO sex determining mechanisms.…”