Untersuchungen über die Entstehung der Parthenogenese bei Solenobia triquetrella F. R. (Lepidoptera, Psychidae)

Summary

• 1. Tetraploid local populations of Solenobia triquetrella arise from the diploid form. A direct transition bisexual → tetraploid parthenogenetic seems not to occur.

• 2. The first step in the transition bisexual → diploid parthenogenetic is a nonstabilized parthenogenesis during which many eggs fail to complete development. The next step is a stabilized parthenogenesis with normal development of all eggs.

• 3. In all tetraploid populations parthenogenesis is stabilized, at least more or less. This is expected because they arise from an already parthenogenetic 2n form.

• 4. For the cytological study of the transition 2n → 4n two local forms have been selected, one of Alpe di Melano in which the transition is nearly finished, and another one from Erlenbach i. Simmental where the transition has just begun.

• 5. It can be demonstrated in both local forms that diploid parthenogenesis is conected with an inhibitory effect, manifesting itself among others in a deficiency in the cortical ooplasm. In the form from Alpe di Melano in addition there exists a lack of “Richtungsplasma” (= plasm containing the spindles of the maturation divisions).

• 6. In the form of Alpe di Melano consequencies of this inhibitory effect are disturbances in the maturation divisions which are followed by fusions of some (or all ?) of the resulting nuclei leading to new chromosome constitutions.

• 7. In the form of Erlenbach the maturation divisions are normal; however, the inhibitory effect, which is here expressed ad a later stage, manifests itself in nuclear fusions at the blastoderm stage or later. Here the fusions have been studied in detail. Among the new nuclear constitutions 4n dominates. Most successful are those fusions taking place in early stages of oogenesis.

• 8. These fusions result in egg batches containing besides diploid eggs also tetraploid ones.

• 9. This is the origin of tetraploid parthenogenesis in Solenobia triquetrella.

• 10. With tetraploidization the inhibition is overcome. It is doubtful whether this will remain the case after many generations.

• 11. The inhibition seems also to disappear in the offspring of the cross 2n parthenogenetic ♀ × ♂. This is, however, only a provisional result.

• 12. The transition diploid parthenogenetic → tetraploid proceeds from causes inherent in the mode of parthenogenesis.

• 13. External factors certainly do not play a primary role in this transition, but may accelerate or retard the onset of the inhibition in the diploid strains, though there is no clear cut proof for their interaction.

• 14. It might be that parthenogenetic multiplication is always connected with inhibitory effects and that the inhibition is overcome by polyploidisation. If so we understand that in the animal kingdom parthenogenesis and polyploidy are very often related.