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

Abstract

The knowledge of cytogenetics in the harvestmen family Phalangiidae has been based on taxa from the Northern Hemisphere. We performed cytogenetic analysis on Guruia africana (Karsch, 1878) (2n=24) and four species of the genus Rhampsinitus Simon, 1879 (2n=24, 26, 34) from South Africa. Fluorescence in situ hybridization with an 18S rDNA probe was used to analyze the number and the distribution of this cluster in the family Phalangiidae for the first time. The results support the cytogenetic characteristics typical for the majority of harvestmen taxa, i.e. the predominance of small biarmed chromosomes and the absence of morphologically well-differentiated sex chromosomes as an ancestral state. We identified the number of 18S rDNA sites ranging from two in R. qachasneki Kauri, 1962 to seven in one population of R. leighi Pocock, 1903. Moreover, we found differences in the number and localization of 18S rDNA sites in R. leighi between populations from two localities and between sexes of R. capensis (Loman, 1898). The heterozygous states of the 18S rDNA sites in these species may indicate the presence of XX/XY and ZZ/ZW sex chromosomes, and the possible existence of these systems in harvestmen is discussed. The variability of the 18S rDNA sites indicates intensive chromosomal changes during the differentiation of the karyotypes, which is in contrast to the usual uniformity in chromosomal morphology known from harvestmen so far.

Evolutionary insights into the genomic organization of major ribosomal DNA in ant chromosomes

“…In eukaryotes, it is common to observe variations in the number of rDNA clusters and the location of these genes in the chromosomes within genera (Sánchez‐Gea et al ., 2000; Gross et al ., 2010; Cabral‐de‐Mello et al ., 2011; Gokhman et al ., 2014; Mazzoleni et al ., 2018), among populations (Panzera et al ., 2014; Ferreti et al ., 2019; Menezes et al ., 2019), and sexes of the same species (Nakayama et al ., 2001; Šťáhlavský et al ., 2018). The possession of terminal rDNA clusters seems to be a common trait among mammals, fish, and molluscs, but less so in arthropods (Sochorová et al ., 2018).…”

Morphological and cytogenetic characteristics of Neobisium (Blothrus) slovacum Gulička, 1977 (Pseudoscorpiones, Neobisiidae), the northernmost troglobitic species of the subgenus Blothrus in Europe

“…Interestingly, two pairs of 18S rDNA clusters were identified in N.slovacum , even though one pair is considered to be the ancestral state for arachnids (Forman et al 2013). However, a multiplication of the 18S rDNA clusters seems to be frequent, at least in arachnids with limited dispersal ability (Svojanovská et al 2016, Šťáhlavský et al 2018a). In such groups the variability in the number and position of rDNA clusters suggests intensive chromosomal changes that may also be expected in N.slovacum , in view of its subterranean habitat.…”

“…For the identification of rDNA clusters, FISH with an 18S rDNA probe was used for all three males. This probe was prepared from the scorpion Euscorpiussicanus (Koch, 1837), as described by Šťáhlavský et al (2018a). The probe was labelled by PCR with biotin-14-dUTP (Roche) using a Nick Translation Kit (Abbott Molecular) following the manufacturer’s guidelines.…”

“…Harrison et al 2014) arachnid groups. However, cytogenetic techniques can also be useful for the identification of cryptic species within various orders of arachnids, such as harvestmen (Šťáhlavský et al 2018a), spiders (Řezáč et al 2018), scorpions (Šťáhlavský et al 2018b) and pseudoscorpions (Zaragoza and Šťáhlavský 2008). This is especially notable in some species of edaphic pseudoscorpions characterized by limited dispersal ability, for which distinct karyotypes may be found even in very close localities (Kotrbová et al 2016).…”

Cytogenetic analysis of three Ctenidae species (Araneae) from the Amazon

“…These additional markers were shown to be relatively minor when compared to that found in the other Ctenus species of the current study, as well as those available in the literature. Such data suggest that these alterations can be caused by chromosomal rearrangements, insertions by transposable elements or ectopic recombination, all processes that could, potentially, be involved in karyotypic differentiation and new species emergence (Stáhlavsky et al, 2018).…”