Diffuse centromere and chromosome polymorphism in haplogyne spiders of the families Dysderidae and Segestriidae

The karyotypes of several individuals of Dysdera crocata C.L. Koch 1838 (Dysderidae), Ariadna boesenbergi Keyserling 1877, and Segestria ruficeps Guérin 1832 (Segestridae) are described. Diffuse centromeres were observed in the 3 species. D. crocata and A. boesenbergi exhibit chromosome number polymorphism, with the presence of trivalent chromosomes in the first metaphase in some individuals. They also show testicular cysts with polyploid spermatogonia and spermatocytes. The haploid chromosome number for these 2 species varies between n = 3 + X and n = 6 + X. The first meiotic division in D. crocata is equational while the second meiotic division is reductional for trivalents and the X chromosome. The first meiotic division in A. boesenbergi is equational for trivalents, and reductional for the X, while the second division is reductional for hemi-trivalents and equational for the X. In S. ruficeps the haploid chromosome number is n = 6 + X(1)X(2), and the first division is reductional for the Xs. The evolution of karyotypes within haplogyne spiders is discussed in relation to the origin of diffuse centromeres.