The genetic structure of a cyclical parthenogen: Brachionus plicatilis species complex

R. Ortells, A. Gomez, M. Serra-2003

Abstract :

Recently, an effort has been made to unify more than thirty years of population genetic studies of aquatic cyclical parthenogens in a model that takes into consideration three factors as crucial in determining their genetic structure : size of resting egg banks, length of the growing season and strength of clonal selection. Four species from the Brachionus plicatilis species complex will be used to assess the importance of these factors. Genotypic diversity and heterozygosity estimates obtained from allozyme data recorded in a temporal survey of four Mediterranean ponds will be analysed in the light of this unifying model. We will show that our results are concordant with the theoretical expectations of a negative correlation between genotypic diversity and the average length of the growth season. The size of resting egg banks and fluctuating changes in the selective regime should be therefore crucial in order to maintain the genetic diversity observed in our zooplankton populations. Furthermore, we will discuss to what extent the cyclically parthenogenetic life cycle together with the type of habitats these organisms inhabit can explain the patterns of within-population genetic diversity and among-population genetic differentiation observed in this system.

(Max Planck Institut für Limnologie, Postfach 165, D-24302 Plön, Germany, e-mail : ortells@mpil-ploen.mpg.de)

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