The first cytogenetic characterization of the poisonous black widow spider Latrodectus gr. curacaviensis from Brazil, with chromosomal review of the family Theridiidae (Arachnida, Araneae).

In this paper we present, for the first time, cytogenetical data on Latrodectus gr. curacaviensis (Theridiidae) from Brazil, as well as the first data on meiosis and sex chromosome system of this genus. Testes were submitted to colchicine, hypotonic, and fixation treatment, and chromosomal preparations were stained with Giemsa solution. The analysis showed 2n=26 telo/acrocentric chromosomes in spermatogonial metaphases. Metaphase I exhibited 12 autosomal bivalents and two sex chromosome univalents (12II + X(1)X(2)). All bivalents revealed one terminal chiasma. Metaphases II confirmed the sex chromosome system, showing 12 autosomes or 12 autosomes plus two X chromosomes, respectively. Male karyotype prevailing in theridiids is formed by 2n=22 chromosomes, including sex chromosome system X(1)X(2) in all species. The Latrodectus species of the geometricus clade analyzed until now showed smaller diploid number (2nfemale symbol=16 and 2nfemale symbol=18) than the species of the mactans clade (2nfemale symbol=24 and 2nfemale symbol=26). Thus, according to the chromosome number, the examined Latrodectus species seems to be related to the mactans clade.