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 male = 24), Ctenidae and Oxyopidae (2n male = 28), Sparassidae (2n male = 42), Gnaphosidae, Trachelidae and Trochanteriidae (2n male = 22), and Salticidae (2n male = 28). On the other hand, we identified interspecific variability within Hersiliidae (2n male = 33 and 35), Oecobiidae (2n male = 19 and 25), Selenopidae (2n male = 26 and 29) and Theridiidae (2n male = 21 and 22).
We examined the karyotypes of Ammoxenidae and Gallieniellidae for the first time. Their diploid counts (2n male = 22) correspond to the superfamily Gnaphosoidea and support their placement in this lineage.
On the other hand, the karyotypes of Prodidominae (2n male = 28 and 29) contrast with all other Gnaphosoidea. Similarly, the unusually high diploid number in Borboropactus sp. (2n male = 28) within the otherwise cytogenetically uniform family Thomisidae (mainly 2n male = 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, X(1)X(2)0 and X(1)X(2)X(3)0) were also detected among the studied taxa.