Fitness decline under relaxed selection in captive populations

We compared life-history schedules among populations of the housefly (Musca domestica L.) maintained in the laboratory under curtailed life span, such that selection on mutations that affected only late-life fitness traits was reduced As a result of this regime, late-life (but not early-life) fecundity declined within a few generations. The results suggest that if captive populations are maintained with minimal selection, either by direct manipulation of the environment or by equalizing family contributions, the increased frequency of potentially deleterious mutations may rapidly lower the ability of these populations to exist under natural conditions. This would be independent of population size, so expanding captive populations would not alleviate potential fitness reductions due to relaxed selection.