Polyploidy and Parthenogenesis in Nature and Experiment. B.L. Astaurov’s Contribution to the Development of Concepts on the Evolution of Polyploidy

The theoretical concepts developed by B.L. Astaurov were the result of his research exploring the phenomenon of artificial parthenogenesis in autotetraploid mulberry silkworm Bombyx mori, as well as alloploids of B. mori and B. mandarina. His hypothesis on the origin of natural polyploidy was that the ‘failure’ to duplicate the genome in animals with sex heterochromosomes could be overcome by alternating polyploidy, parthenogenesis and hybridisation. Alloploids more easily overcome the sterility barrier, and a necessary step in speciation is the asexual reproduction of triploids. This complex pattern of speciation was inferred from a large number of crosses and an in-depth analysis of several key characteristics, including fecundity, the morphological features of cocoons, and the chromosome number of autoploid and alloploid lines of bisexual and parthenogenetic silkworms. Despite the millennial interest in silk production and a century and a half of cytological studies of this unique object of developmental biology, the cytogenetic mechanisms ensuring the emergence of parthenogenetic lines and the inheritance of polyploid genomes in silkworms remain unknown.