Cytological and developmental analysis of tychoparthenogenesis in locusta migratoria

Abstract

A number of females of Locusta migratoria have shown tychoparthenogenetic reproduction (a kind of accidental thelytoky) characterized by: (i) a female-biased primary sex ratio; (ii) the production of embryos with abnormal ploidy levels, mainly haplodiploid mosaics; (iii) a longer time for embryo development; and (iv) the capability of producing female offspring that reproduced in the absence of males. Perfect diploidization is not essential for parthenogenetic embryos to reach the adult stage but a great majority of embryo cells must be diploid to complete properly embryogenesis and hatch. In addition, diploidy is apparently necessary to the ovary of parthenogenetic females so that eggs laid without mating can hatch. Cytological analyses of embryos at different developmental ages have shown that parthenogenetic embryos begin haploid and gradually become diploid, thus passing through a haplodiploid mosaic stage. The most likely mechanism for ploidy restoration is the restitution of the sister products of cleavage mitoses, although our results show that cell fusion could be another mechanism, the relative importance of which remains to be tested in future work. Although parthenogenetic females showed a fecundity comparable to that of sexual females, their reproductive output was significantly lower because of a decrease in the number of embryos per pod and a consequent decrease in the rate of embryo production. © 1995 The Genetical Society of Great Britain.