Cytology of Parthenogenesis inBacillus whiteiandBacillus lynceorum(Insecta Phasmatodea)

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Abstract
We investigated the maturation divisions of two obligate parthenogenetic natural interspecific hybrids: the diploid B. whitei and the triploid B. lynceorum. B. whitei shows two maturation divisions which produce 4 viable haploid nuclei. At the telophase II two non-sister nuclei come into contact and fuse to restore the diploid chromosome number and the maternal genetic structure. On the other hand, in the triploid B. lynceorum, pachytenic oocytes undergo an extra DNA doubling which allows the formation of a somatic number of autobivalents. Two divisions in rapid succession result in a pronucleus with the somatic number of unistranded chromosomes and two quickly degenerating polar bodies: this mechanism maintains the maternal cytological and genetic structure in the offspring. These cytological findings fully support the genetic features ascertained for the two hybrids and provide evidence of their different and very likely independent meiotic adaptations to parthenogenetic reproduction.