Pairing and segregation of the sex chromosomes in X1X2-males of Dysdercus intermedius with a note on the kinetic organization of Heteropteran chromosomes

Abstract

The existence of an X1X2-mode of sex determination is confirmed by a study of all meiotic stages in the male cotton stainer (X1X2) and pertinent stages in the female (X1X1X2X2). In the male, the X-chromosomes are heterochromatic and pair end-to-end in early meiotic prophase. At diakinesis, they disjoin and align side-by-side in the center of the spindle, forming a pseudotetrad. Anaphase I is equational for the sex chromosomes. At late anaphase or telephase, X1 and X2 join end-to-end but form spindle fiber connections to only one of the poles of the metaphase II spindle, leading to one daughter cell without X chromosomes and one with both X1 and X2. An attempt is made to explain sex chromosome pairing and orientation on the basis of a telocentric organization of meiotic chromosomes. The apparent differences in the kinetic organization of mitotic and meiotic chromosomes in Heteroptera are discussed.

Sex Chromosome Evolution in Cotton Stainers of the Genus <i>Dysdercus</i> (Heteroptera: Pyrrhocoridae)

“…In previous reports, the synaptic behaviour of heteropteran sex chromosomes during male meiosis was studied by electron microscopy and silver staining of meiotic axes. The sex chromosomes of several species with different sex chromosome systems (X0, XY, X 1 X 2 0, and X 1 X 2 Y) failed to show the presence of regular axial elements (AEs) during the first meiotic prophase, either in spreads or in sections [Ruthmann and Dahlberg, 1976;Solari, 1979;Suja et al, 2000;Pigozzi and Solari, 2003;Toscani et al, 2008]. These results led to the hypothesis that the lack of formation of AEs along the heteropteran sex chromosomes is somehow related to their equational division at anaphase I (post-reductional behaviour) [Solari, 1979;Suja et al, 2000;Pigozzi and Solari, 2003;Toscani et al, 2008].…”

Cytological Studies of the Coreidae and Alydidae (Hemiptera: Heteroptera). I. Male Meiosis in Malaysian Species

“…In Syromastes DARLINGTON (1939) thought this to be the result of touch-and-go pairing promoting the adherence of the X1 and X2, together with spindle fibres being produced to only one pole. The latter was confirmed by RuTHMANN and DAHLBERG (1976) in sectioned preparations of Dysdercus intermedius. In this species the X's move together ahead of the autosomes to one pole, whereas in coreid species they frequently lag behind the autosomes and lie away from the compact telophase ring.…”

“…Regular segregation of both X chromosomes to one pole in second anaphase is found in the coreid species, as in Dysdercus X1:MO species (MENDES 1949;RuTHMANN and DAHLBERG 1976) and in Triatominae XDCN species (UESHIMA 1966). In Syromastes DARLINGTON (1939) thought this to be the result of touch-and-go pairing promoting the adherence of the X1 and X2, together with spindle fibres being produced to only one pole.…”

“…Nor can resolution of chiasmata cause the fine chromatin threads which persist between the ends of separating autosomal chromatids, as suggested by CoMINGS and OKADA (1972) from electron microscope studies, since these are present also between achiasmate m-chromosomes. More feasible is their alternative that the threads comprise a mixing of fibres of the separating holocentric chromosomes, although RuTHMANN and DAHLBERG (1976) interpret them to be telomeric connections between monocentric chromosomes.…”

“…This lateral pairing was suggested by WHITE (1954) to depend possibly on some degree of homology between the X's, or on a non-specific attraction between heterochromatic material. RuTHMANN and DAHLBERG (1976), however, proposed a telomeric contact between sister chromatids, and possible proteinaceous bonds between the X-univalents of Dysdercus intermedius.…”