An experimental assessment of artificial within-family selection for fitness in conservation programs

Equalizing familiar contributions is the simplest recommended strategy to maintain genetic diversity in conservation programs. However, this method implies a relaxation of natural selection and the possibility of accumulation of deleterious mutations. Computer simulations have shown that performing selection within families for fitness traits in a conservation program can be useful to alleviate such problems. We thus carried out an experiment with the model species Drosophila melanogaster in order to assess whether or not selection for fitness traits can be useful. We considered a fitness trait (pupa productivity) that was first checked to perform as a typical fitness component. The trait showed an inbreeding depression of 1.2 per 1 % increase in inbreeding and an asymmetrical response to selection with average realized heritabilities of about 0.04 in the upward direction and an order of magnitude larger (0.36) in the downward direction. The management experiment indicated that artificial within-family selection for fitness had only a marginal success for two reasons. First, there was not an appreciable decline in fitness across the experiment despite the low population sizes assumed (N = 10 or 20), even in the population not subjected to selection. This result is compatible with fitness models which imply the segregation of few deleterious mutations of large effect. Second, artificial selection within families had a limited impact on the trait, as one expects for a typical fitness component with very low heritability.