Parthenogenetic insects are in general polyploid. These polyploid parthenogenetic forms seem to be superior competitors compared to their diploid and sexual relatives. Numerous studies have shown a surprisingly high clonal diversity in parthenogeinetic insects. We have studied Otiorhynchus scaiber, a common flightless weevil. O. scaber consists of three forms: one diploid sexually reproducing form with a very limited distribution and two widely distributed polyploid parthenogenetic forms. All forms, diploids and polyploids, coexist within the central area of distribution where both genetic and clonal diversity are highest. Diversity and degree of ploidy decrease towards the margin of distribution, so that only tetraploids inhabit the margins. This geographical pattern of distribution is a common phenomenon in parthenogenetic animals with different ploidy levels. We suggest that the high clonal diversity in populations of O. scaber is due to a continuous transition from diploid sexuality to triploid and finally to tetraploid parthenogenesis. We propose that the transition is caused by chance fertilisations of unreduced eggs.
Lakovaara, S. (Department of Genetics, University of Oulu, SF‐90100 Oulu 10, Finland), Saura, A., Lankinen, P., Pohjola, Liisa and Lokki, J. The use of isoenzymes in tracing evolution and in classifying Drosophilidae. Zool. Scr. 5 (3–4): 173–179, 1976.—Studies on the genetic constitution of natural populations of organisms have shown that these populations are extensively polymorphic at gene loci coding for enzymes. Much of this polymorphism detected by electrophoresing enzyme proteins is, however, not useful in classifying organisms, even though in general species differ from each other more than populations within a species. Good diagnostic characters are monomorphic species‐specific genes and their products. Finding these characters requires a thorough study of many populations of the species being studied. Once these characters have been found they can be used in assigning single individuals into different taxa. Electrophoresis of enzymes and allozyme differences between species can also be used in tracing the evolution of organisms. On the basis of allozymes a new phylogeny is proposed for the Drosophila obscura species group. Traditionally this group has been divided into two subgroups, obscura and affinis. Genetic characters divide this species group into three evolutionary lineages. The first lineage comprises the Eurasian obscura subgroup, the second the American affinis subgroup and the third the American obscura subgroup. D. alpina and D, helvetica, which belong to the obscura and affinis subgroups, respectively, are not appreciably related to any other species.
The enzyme gene variability within parthenogenetic clones of Acyrtosiphon pisum has been followed by gel electrophoresis. No variation was observed within any clone. One enzyme locus was found to vary between clones. No evidence was found to support gene recombination due to the alleged endomeiosis. This hypothesis is proven to be also theoretically untenable. The low average heterozygosity in aphids is explained as a result of directional selection operating upon the parthenogenetic aphid clones, as a consequence of which the heterozygosity is lowered.
Otiorhynchus scaber is a common weevil throughout northern Europe. It is tetraploid and parthenogenetic in this area. A total of 75 electrophoretically definable clones have been identified in northern Europe and they all appear to represent a monophyletic lineage. 0. scuber is a flightless inhabitant of the climax community, the spruce forest. Rarefaction and similarity index has been used to measure clone diversity and its distribution. Clone diversity is highest in the Southern Boreal and the Middle Boreal zones and decreases towards north and south. The distribution of single clones appears to be associated with the biotic zonation of northern Europe. This implies that different clones are adapted to different environments.
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