Haploidy and aberrant spermatogenesis in a coleopteran, Micromalthus debilis LeConte

Abstract

AbstractThe coleopteran Micromalthus debilis LeConte has two additional female reproductive forms besides the male and female adults. One of these is a paedogenetic viviparous female which produces female offspring by diploid parthenogenesis; the other is a paedogenetic ovoviviparous female which produces males by haploid parthenogenesis; The male has been shown to be somatically haploid in both early and late stages of development, while all three female types are diploid. The first spermatocyte division is completely abortive as regards division of chromosomes and cell. However, a very characteristic unipolar spindle is regularly formed. The chromosomes of the first spermatocyte anaphase move away from the single pole with their attachment regions hindermost. The spindle consists of ten fibers, each one connecting a chromosome with a single pole. They elongate during the anaphase. The second spermatocyte division is apparently normal in all respects and it ultimately results in two normal sperm. It has been shown that the theories of Belar, Bleier and Schaede concerning the problem of chromosome movement are deficient in view of the peculiarities of this monocentric mitosis.