IS MUTATION ACCUMULATION A THREAT TO THE SURVIVAL OF ENDANGERED POPULATIONS

The accumulation of new deleterious mutations has been predicted to co nstitute a significant threat to the survival of finite sexually repro ducing populations. Three measures of genetic load were made on popula tions of Drosphila melanogaster maintained at effective population siz es of 25, 50, 100, 250, and 500 for 45 or 50 generations and their out bred base population and a new sample from the same wild population. G enetic loads were measured as fitness differentials between inbred and non-inbred lines derived from each population under both benign (prod uctivity of single pairs) and competitive (competitive index) conditio ns. No trend of smaller populations exhibiting greater genetic loads t han larger ones was observed under either benign or competitive condit ions. Further, genetic loads were similar in captive and wild populati ons. Frequencies of deleterious and lethal alleles on chromosome II we re measured by making the chromosome (approximately 40% of the genome) homozygous using a marked balancer stock. Neither deleterious nor let hal allele frequencies exhibited a relationship with population size. The accumulation of detrimental mutations does not appear to pose a si gnificant threat to finite sexual populations with effective sizes of 25 or more over the 100-200 year time frames considered in most wildli fe conservation programs.