Cytogenetical characterization of six orb-weaver species and review of cytogenetical data for Araneidae

Abstract

The family Araneidae is the third largest among spiders and the third most studied from a cytogenetical point of view. In spite of this, only 2% of all araneids have been karyotyped. The majority of araneids analyzed possess 2n = 24 chromosomes in males; however, the study of additional species could reveal unusual karyotype characteristics. Thus, the aim of this work is to analyze chromosomally, for the first time, six species belonging to three araneid genera from Brazil. The specimens of Alpaida leucogramma (White 1841), Alpaida truncata (Keyserling 1865), Alpaida veniliae (Keyserling 1865), Parawixia kochi (Taczanowski 1873), Parawixia velutina (Taczanowski 1878) and Wagneriana sp. were collected in Parque Nacional de Ilha Grande and in the municipality of Rio Claro. The gonads were treated with colchicine and hypotonic solution before fixation with Carnoy I solution. The results were 2n male = 24 (11II+X(1)X(2)) in A. leucogramma and P. velutina, and 2n male =- 22 (10II+X(1)X(2)) in A. truncata, A. veniliae, P. kochi and Wagneriana sp. When the chromosomal morphologies were established, we observed telocentric chromosomes in all specimens save one female specimen of P. velutina. The univalent sex chromosomes were easily recognized on diplotenes. The unpaired metacentric element found in one female specimen of P. velutina with 2n = 25 probably arises by centric fusion/fission. Araneidae is a megadiverse family composed of similar to 3000 species distributed mainly in the tropics; thus the analysis of more species may provide new insights about orb-weaver chromosome evolution.