Clone diversity in the polyploid weevil Otiorhynchus scaber

Parthenogenetic insects are in general polyploid. These polyploid parthenog enetic forms seem to be superior competitors compared to their diploid and sexual relatives. Numerous studies have shown a surprisingly high clonal di versity in parthenogenetic insects. We have studied Otiorhynchus scaber, a common flightless weevil. O. scaber consists of three forms: one diploid se xually reproducing form with a very limited distribution and two widely dis tributed polyploid parthenogenetic forms. All forms, diploids and polyploid s, coexist within the central area of distribution where both genetic and c lonal diversity are highest. Diversity and degree of ploidy decrease toward s the margin of distribution, so that only tetraploids inhabit the margins. This geographical pattern of distribution is a common phenomenon in parthe nogenetic animals with different ploidy levels. We suggest that the high cl onal diversity in populations of O. scaber is due to a continuous transitio n from diploid sexuality to triploid and finally to tetraploid parthenogene sis. We propose that the transition is caused by chance fertilisations of u nreduced eggs.