Oogenetic variability and spontaneous parthenogenesis in the silkworm Bombyx mori L.

Abstract

Aims. The change of the mature oocyte developmental ability along the ovariole has been studied to find oogenetic basis for intraclonal variation. Methods. Parthenoclone P29 reproduced by ameiotic parthenogenesis (Astaurov, 1940) was used. The percentage of complete serosa formation among spontaneously developing eggs laid day by day during 12 days by virgin P29 females or among eggs mechanically extirpated from the ovarioles was taken as an estimate of developmental potential for the oocytes. Results. The developmental oocyte potential was shown to depend on the oocyte position in the ovariole, its maximum being among the first formed oocytes and located nearest to the ovipositor and its minimum being among the youngest mature oocytes. The mechanical irritation stimulates eggs to develop and its effect also depends on the oocyte position in the ovariole, the minimum being in the middle region of the latter. Conclusion. The shown absence of equipotentiality of the mature oocytes in the ovariole can be considered as the cause of intraclonal variability in the silkworm and can be used for analysis of some basic concepts of genetics and epigenetics.

Key words: parthenogenesis, clones, intraclonal variation, oogenesis, silkworm.