No abstract

As part of a programme to determine the importance of the loss of genetic variation for the probability of population extinction, the amount of allozyme variation was determined in 14 populations of Salvia pratensis and in 12 populations of Scabiosa columbaria. Significant correlations were found between population size and the proportion of polymorphic loci (Salvia: r= 0.619; Scabiosa: r= 0.713) and between population size and mean observed number of alleles per locus (Salvia: r =0.540; Scabiosa: r = 0.819). Genetic differentiation was substantially larger among small populations than among large populations: in Salvia GST was 0.181 and 0.115, respectively, and in Scabiosa 0.236 and 0.101, respectively. The results are discussed in relation to genetic drift, inbreeding and restricted gene flow.

SUMMARYStudies of the morphological polymorphism for the expression of male sterility in the gynodioecious species Plantago lanceolata revealed two separate series of stamen forms from sterile to fertile. The first type of complete male sterility (MSI) shows a disturbed development of the stamens, which are strongly reduced in size. The second type (MS2) has stamens which are petaloid. In the latter type the corolla and sometimes the pistil are also affected. Evidence is presented that these differences in expression of male sterility are cytoplasmically determined. The plasmon types are designated R and P respectively. In each plasmon type a series of intermediate sex forms occurs. Field counts showed that these intermediates are a non-negligible proportion of most populations. On the average MS1 reaches higher frequencies than MS2. Twenty two out of 27 populations appeared to be polymorphic for plasmon type. The remaining five populations are probably fixed for plasnion P and their distribution over the habitats studied suggests that the fitnesses of the different sex genotypes depend on environmental conditions.

Understanding the origin, maintenance and significance of phenotypic variation is one of the central issues in evolutionary biology. An ongoing discussion focuses on the relative roles of isolation and selection as being at the heart of genetically based spatial variation. We address this issue in a representative of a taxon group in which isolation is unlikely: a marine broadcast spawning invertebrate. During the free-swimming larval phase, dispersal is potentially very large. For such taxa, small-scale population genetic structuring in neutral molecular markers tends to be limited, conform expectations. Small-scale differentiation of selective traits is expected to be hindered by the putatively high gene flow. We determined the geographical distribution of molecular markers and of variation in a shell shape measure, globosity, for the bivalve Macoma balthica (L.) in the western Dutch Wadden Sea and adjacent North Sea in three subsequent years, and found that shells of this clam are more globose in the Wadden Sea. By rearing clams in a common garden in the laboratory starting from the gamete phase, we show that the ecotypes are genetically different; heritability is estimated at 23%. The proportion of total genetic variation that is between sites is much larger for the morphological additive genetic variation (Q ST ¼ 0.416) than for allozyme (F ST ¼ 0.000-0.022) and mitochondrial DNA cytochrome-c-oxidase-1 sequence variation (U ST ¼ 0.017). Divergent selection must be involved and intraspecific spatial genetic differentiation in marine broadcast spawners is apparently not constrained by low levels of isolation.

Strains of Drosophila melanogaster homozygous either for the AdhF or the Adhs allele, were kept on food supplemented with ethanol. After 90 generations these strains (FFE and SSE) were tested for tolerance to ethanol and compared with control strains (FFN and SSN) from regular food. The E strains showed increased tolerance to ethanol, both in the adult and in the juvenile life stages. In the adults the increase in tolerance was not accompanied by an increase in ADH activity. In the juvenile life stages there were significant differences in ADH activity between the E and N strains, both on regular food and on food containing ethanol. However, ADH activity was not the only factor involved in the increased tolerance to ethanol.The Adh genotype of the mother was of paramount importance to egg-to-adult survival because of a maternal effect on ethanol tolerance in the eggs and first instar larvae. Furthermore developmental times of the E strains were longer than those of the corresponding N strains. It is concluded that the adaptation to ethanol-containing food was not realised in the same way in the FFE and SSE strains.