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

Abstract

Spiders represent one of the most studied arachnid orders. They are particularly intriguing from a cytogenetic point of view, due to their complex and dynamic sex chromosome determination systems. Despite intensive research on this group, cytogenetic data from African spiders are still mostly lacking. In this study, we describe the karyotypes of 38 species of spiders belonging to 16 entelegyne families from South Africa and Namibia. In the majority of analysed families, the observed chromosome numbers and morphology (mainly acrocentric) did not deviate from the family-level cytogenetic characteristics based on material from other continents: Tetragnathidae (2n♂ = 24), Ctenidae and Oxyopidae (2n♂ = 28), Sparassidae (2n♂ = 42), Gnaphosidae, Trachelidae and Trochanteriidae (2n♂ = 22), and Salticidae (2n♂ = 28). On the other hand, we identified interspecific variability within Hersiliidae (2n♂ = 33 and 35), Oecobiidae (2n♂ = 19 and 25), Selenopidae (2n♂ = 26 and 29) and Theridiidae (2n♂ = 21 and 22). We examined the karyotypes of Ammoxenidae and Gallieniellidae for the first time. Their diploid counts (2n♂ = 22) correspond to the superfamily Gnaphosoidea and support their placement in this lineage. On the other hand, the karyotypes of Prodidominae (2n♂ = 28 and 29) contrast with all other Gnaphosoidea. Similarly, the unusually high diploid number in Borboropactus sp. (2n♂ = 28) within the otherwise cytogenetically uniform family Thomisidae (mainly 2n♂ = 21–24) supports molecular data suggesting a basal position of the genus in the family. The implementation of FISH methods for visualisation of rDNA clusters facilitated the detection of complex dynamics of numbers of these loci. We identified up to five loci of the 18S rDNA clusters in our samples. Three different sex chromosome systems (X0, X1X20 and X1X2X30) were also detected among the studied taxa.

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

“…Mapping of this cluster often revealed a single NOR site, which is probably an ancestral pattern in arachnids [36]. The number of NOR/rDNA loci has increased in some arachnid clades during their evolution [76,77,81,87]. In haplogyne spiders, these loci are also frequently placed on sex chromosomes [77,90].…”

“…The major rDNA cluster (45S rDNA) is by far the most utilized molecular chromosomal marker across diverse eukaryotic organisms, and especially in non-model groups [72][73][74]. The major rDNA cluster visualized either by 18S or 28S rDNA probes has already been localized in some spiders [36,46,73,[75][76][77], scorpions [45,76,[78][79][80][81][82], pseudoscorpions [83], harvestmen [84][85][86][87], ticks [73,88,89], and an amblypygid [18]. Mapping of this cluster often revealed a single NOR site, which is probably an ancestral pattern in arachnids [36].…”

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

“…So far, NORs have only been detected in a low number of spider species (see Forman et al 2013;Král et al 2013 for references), especially by the means of FISH (see Šťáhlavský et al 2020;Reyes Lerma et al 2021 for references). In pholcids, however, NOR patterns have been determined recently in many species by FISH (Ávila Herrera et al 2021), which makes it possible to contextualize our data with previous knowledge on the NOR evolution in this family.…”