Unveiled chromosomal diversity in the Araneidae (Araneomorphae): the highest diploid number among entelegynes and the first record of the X*1 X*2 X*3 X*4 Sex Chromosome System in the family

Abstract

Araneidae is one of the most specious spider families, but few karyotype studies exist (1.9%), and some clades lack chromosomal data, with many uncertain evolutionary relationships. This study presents the karyotype analysis of eight Araneidae species (Acacesia benigna, Actinosoma pentacanthum, Alpaida bicornuta, Dubiepeira sp., Gasteracantha cancriformis, Parawixia bistriata, Verrucosa meridionalis, and Verrucosa scapofracta), aiming to contribute to the discussion of evolutionary scenarios. Gonads were treated with colchicine, hypotonization, slide preparation, and Giemsa staining. Most species showed 2n♂ = 24 (11II + X1X2), except Dubiepeira sp. (2n♂ = 41, 19II + X1X2X3) and Verrucosa species (2n♂ = 47, 22II + X1X2X3 in V. meridionalis and 2n♂ = 50, 23II + X1X2X3X4 in V. scapofracta). The species exhibit acro/telocentric chromosomes. The 2n♂ = 24, X1X2 is the most common karyotype in Araneidae. This work provides the first chromosomal data for the “Micrathenines” clade, the highest diploid number among Entelegynes (2n♂ = 50), and the first record of X1X2X3X4 in Araneidae. Chromosome data suggest fission events in the origin of Verrucosa karyotypes and a close relationship between Dubiepeira and Araneus ventricosus. Alpaida bicornuta is cytotaxonomically distinct from other Alpaida species.