Distance segregation and compound sex chromosomes in mantispids (Neuroptera:Mantispidae).

Abstract

The sex chromosomes segregate precociously in prometaphase I of male meiosis, without prior synapsis or any physical connection, in 4 species of American mantispids (Neuroptera: Mantispidae). Segregational movements are interpolar, and are implemented through chromosomal fibers. Univalent autosomes, present from diakinesis on in several species, are capable of a similar distance segregation in prometaphase. The sex chromosomes are XX ♀ —XY ♂, as is characteristic of the Order, with the exception of Entanoneura phthisica in which both elements are compound —X1X2X3Y1Y2Y3in the male, and X1X1X2X2X3X3 in the female. In tetraploid sectors of gonial origin in testes of this species no sex bivalents are formed; a distance segregation of 6 sex univalents to each pole is effected, but — as observed in the one individually identifiable pair — segregation separates complete homologues, Y1 from Y1, X1 from X1, etc. In all species the male meiotic spindle is formed by the collocation of individual chromosomal spindle units within which bivalents become deformed; the timing and degree of deformation vary with the species. In karyotype the American species conform to a common pattern with the known Japanese and European species; diploid numbers range only from 18 to 22, and each complement carries the family insigne of one pair of disproportionately large autosomes in a set of small and rather uniformly sized chromosomes.