Effective population size in Drosophila subobscura: ecological and molecular approaches

The effective population size (Ne) represents the number of individuals that can contribute genes equally to the next generation and is usually smaller then the actual size of a population. The aims of this study were: (i) to assess the Ne for two Drosophila subobscura populations sampled from geographically close, but ecologically and topologically distinct habitats, (ii) to compare the results obtained from two independent approaches for estimating Ne [an ecological (capture-mark-release-recapture) and a molecular (microsatellite data, linkage disequilibrium and heterozygote excess)], and (iii) to obtain a long-term Ne estimation using a variety of mutational models for D. subobscura populations. The ecological method showed that the beech wood population (B) had a significantly larger Ne compared to the oak wood population (O). Observed sex ratio was in favor of females in both populations studied. The microsatellite analysis of populations showed that short-term effective population size in beech wood was larger when compared to population from oak wood, which is in concordance with results obtained by the ecological method. Long term Ne of both natural populations is infinite according to a variety of mutational models. Our results confirmed concordance between ecological and molecular methods in Ne estimation, but also suggested that ecological approach showed less robustness. Molecular approach provides a promising opportunity for more effective monitoring of Ne in Drosophila subobscura. However, the biology, demography and history of the populations may affect different estimators differently so we suggest that ecological and molecular approach should be combined in Ne estimation.