Evolution of asexuality in insects Polyploidy, hybridization and geographical parthenogenesis

Sammanfattning: Asexual reproduction and polyploidy are relatively rare in animals with chromosomal sex determination and always represent a derived condition. To accomplish asexual reproduction several changes in gene expression are required in the mechanism of oogenesis. Polyploidy increases the cell volume and also gives rise to alterations in general physiology. Nevertheless, there are asexual animals that not only survive but seem to be doing better than their sexual progenitors. This is expressed in the distribution pattern called geographical parthenogenesis. Using molecular phylogeny, I here examine the evolution of Otiorynchid weevils, mainly Otiorhynchus scaber and sulcatus in an attempt to trace the evolutionary history and find out what causes the variation in success of different parthenogens. I also evaluate the contribution of asexuality, hybridity and polyploidy as explanations behind geographical parthenogenesis in insects. I conclude that what is called O. scaber is, in fact, a set of geographical polyploids as polyploidy and not asexuality explains the difference in clonal success. I also argue that O. sulcatus is a recently formed clonal species of non-hybrid origin that may well be a good example of a true general purpose genotype. I find little support for asexuality or a hybrid origin as explanations behind geographical parthenogenesis in insects. Finally, I argue that polyploidy in all eukaryotes should be seen as an opportunity for the species evolution, not as a limitation that ensures the demise of the taxa.