Low genetic variability in the ancient asexual ostracod darwinula stevensoni

Abstract

The genetic variability and genotypic (clonal) structure of 34 populations of the ancient asexual Darwinula stevensoni was assayed using allozymes. In this study of 1964 individuals from nine countries in Europe, Israel and South Africa, little genetic variability was found. Out of nine enzyme systems only two revealed sufficient enzyme activity to produce consistent zymograms. Only one locus (Gpi 1) was polymorphic, and only in 14 populations: 83% of all screened individuals from all over Europe shared the same genotype. There was no significant deviation of Hardy—Weinberg equilibrium in 10 out of 14 polymorphic populations, a result unexpected in an asexual species. Among possible causes we discuss null alleles whose presence would make genotype frequencies discordant with Hardy-Weinberg equilibrium. Allele and genotype frequencies were different in lakes and rivers (heterozygotes were dominant in rivers, homozygotes in lakes). Habitat choice might be driven by a different starvation tolerance by different genotypes. © 2004 Taylor & Francis Group, LLC.