Abstract

BRESSA, María José  and  PAPESCHI, Alba Graciela. New contributions to the study of Corixoidea: cytogenetic characterization of three species of Sigara from Argentina and the plausible mechanisms of karyotype evolution within Nepomorpha. Rev. Soc. Entomol. Argent. [online]. 2007, vol.66, n.3-4, pp.81-89. ISSN 0373-5680.

Cytogenetic studies in Heteroptera contribute to the analysis of evolutionary trends within the group. Heteroptera are characterized by the possession of holokinetic chromosomes, different sex chromosome mechanisms and a pair of m chromosomes in some species. In the present work, the male karyotype and meiosis in Sigara denseconscripta (Breddin), S. chrostowskii Jaczewski, and S. rubyae (Hungerford) are described. The three species share a diploid chromosome number of 2n= 24 with a pair of m chromosomes and an XY/XX sex chromosome system. With this study the chromosome number of 30 species of Corixoidea are known and the modal karyotype is 2n= 20+2m+XY in males. The available cytogenetic information in Heteroptera led us to suggest that the presence of a pair of m chromosomes and an XY/XX sex chromosome system could be considered as plesiomorphic for Nepomorpha. The absence of m chromosomes in species of Ochteroidea and Nepoidea, and the sex chromosome systems X0 and X_n0 (male) in species of Corixoidea, Naucoroidea, and Nepoidea should be considered as derived characters, which arose later in evolution.

Keywords : Cytogenetics; Heteroptera; Holokinetic chromosomes; Meiosis; m chromosomes.

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