Evol Ecol Res 3: 969-984 (2001)     Full PDF if your library subscribes.

Mode of reproduction, ploidy and fluctuating asymmetry: comparison of co-existing sexual and asexual freshwater snails

Jukka Jokela,1,2* Senta Niederegger,3 Sonja Negovetic1 and Pia Mutikainen2

1Experimental Ecology, ETH-Zürich, ETH-Zentrum NW, CH-8092 Zürich, Switzerland, 2Department of Biology, University of Oulu, FIN-90014 Oulu, Finland and 3Max-Planck-Institute, Department of Biochemistry, Spemannstrasse 35/11, D-72076 Tubingen, Germany

Address all correspondence to Jukka Jokela, Department of Biology, Box 3000, University of Oulu, FIN-90014 Oulu, Finland.
e-mail: jukka.w.jokela@oulu.fi


We compared fluctuating asymmetry of ecologically similar sexual and asexual freshwater snails (Potamopyrgus antipodarum). The asexual snails are triploid apomictic parthenogens, whereas the sexual snails are diploid. Although earlier studies have shown that the average heterozygosity does not differ between sexuals and asexuals, higher ploidy level and accumulation of mutations may affect the fluctuating asymmetry of asexuals. However, it is unclear how large this genetic effect might be relative to the environmental effects; empirical studies of the effects of genetic stress on fluctuating asymmetry suggest that weak effects are to be expected. Our aim in this study was to contrast the magnitude of variation in fluctuating asymmetry due to environment to that due to ploidy and mode of reproduction. For this purpose, we assessed fluctuating asymmetry in radula morphology of co-existing sexual and asexual females, knowing that the asexuals represented a group of different clonal genotypes. For reference, we also assessed among-population variation in fluctuating asymmetry and contrasted this to among-individual variation in fluctuating asymmetry. The radula is a bilaterally symmetric feeding structure that is composed of repeated rows of teeth. We found significant among-individual variation in fluctuating asymmetry, indicating sufficiently powerful statistical analysis, but we found no statistically significant differences in fluctuating asymmetry between sympatric asexual and sexual snails, or among different snail populations. Our results suggest that genetic effects of ploidy and asexuality on fluctuating asymmetry are too small to be detected against the environmental variation. These results suggest that the asexual and sexual snails respond to external stress factors similarly, at least with respect to the level of fluctuating asymmetry.

Keywords: asexual reproduction, fluctuating asymmetry, mutation load, Potamopyrgus antipodarum, radula.

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