Large variation in mitochondrial DNA of sexual and parthenogenetic Dahlica triquetrella (Lepidoptera: Psychidae) shows multiple origins of parthenogenesis
The present paper terminates the series of investigation (I.–VI.) concerning the development of parthenogenesis inTriquetrella. It reports the F1, F2, F3-results of crosses between diploid parthenogenetic femalesxmales of the bisexual form. The parthenogeneticTriquetrella displays a normal meiosis and has a normal X chromosome apparatus. In spite of this it is thelytokous, since it orginates from the so called “Richtungskopulationskern” (R. K. K.), the fusion product of the two inner polar bodies. This nucleus is always of XO constitution. It blocks further development of the egg nucleus. In the inseminated parthenogenetic egg amphimixis occurs, whereupon the fertilization nucleus blocks further development of the R. K. K. Since the parthenogeneticTriquetrella forms two types of eggs (with and without X) each cross of a diploid parthenogenetic ♀ with a ♂ of whatever origin (P, F1, F2 etc.) should give rise to a normal sex ratio; we indeed obtained this result. The parthenogenetic form has lost to various degrees the ability to inseminate its eggs after copulation. Since all bastard females inseminate normally, a factor must be introduced by the cross, which is dominant over all those degrees of loss, which we know. Bisexual females lay eggs only after copulation. In some parthenogenetic local forms this blockage of egg laying is relieved entirely, in others it is only partly relieved. Thus relief from blockage takes place stepwise. Our quantitative data allow the conclusion, that we are dealing with a dominant mendelian factor. Each degree of blockage relief is transferred in an unaltered fashion according to the following scheme: Eggs of bisexual race, which have been laid without copulation, do not as a rule develop. Development is arrested in metaphase I; in some parthenogenetic local forms this blockage is partly, in others it is entirely relieved. Thus we are dealing with another case of stepwise transition bisexual→unisexual. One could have expected that those factors, which relieve the blockage of egg laying, could also have relieved the developmental blockage of non-inseminated eggs. However, it can be proved that both phenomena are independent from one another. Concerning the nature of those factors, which set into motion development of a non-inseminated egg, we cannot state anything with certainty. We presume that here cytoplasmic factors play the decisive role. The generations which arise from parthenogenetic eggs laid by bastard females can be viewed as an image of the condition of the first parthenogenetic generations which followed and continues to follow bisexual propagation.