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Achiasmatic male meiosis in three Micronecta species (Heteroptera: Nepomorpha: Micronectidae)

Grozeva S., Simov N., Nokkala S.

Abstract. Male meiosis of three water boatmen species Micronecta (Dichaetonecta) scholtzi (Fieber, 1860), M. (Micronecta) poweri (Douglas et Scott, 1869) and M. (Micronecta) griseola Horvath, 1899 (Corixoidea: Micronectidae) was studied pay-ing special attention to the presence or absence of chiasmata. Condensation stage revealed 11 autosomal bivalents consisting of side by side associated homologous chromosomes. At this stage positively heterochromatic X and Y chromosomes were attached to the nucleolus. There were no m-chromosomes. The chromosome number of all species is 2n=22+XY. Side by side association of homologous chromosomes was still seen at late condensation stage. At prometaphase and metaphase I, the bivalents oriented parallel to the equatorial plane and homologous chromosomes are facing opposite poles. Hence, male meiosis in these species is achiasmatic of alignment type. At metaphase II chromosomes showed variable positions in the plate. In M. scholtzi, the Y chromosome is smaller than the X chromosome, while in M. poweri and M. griseola X and Y chromosomes were similar in size. It is suggested that achiasmatic male meiosis and lack of m-chromosomes are cytogenetic features separating the family Micronectidae from the family Corixidae among the superfamily Corixoidea within the infraorder Nepomorpha. It seems plausible that achiasmatic male meiosis has emerged in Heteroptera more than once during their evolution.