An extreme test of mutational meltdown in small populations. Ronny C. Woodruff. Dept Biological Sciences, Bowling Green State Univ, Bowling Green, OH.

   In small populations, deleterious mutations arise and, because of inbreeding and drift, can go to fixation (become homozygous) over time. This slow decline in fitness may ultimately lead to extinctions. This process is called mutational meltdown. We tested mutational meltdown in small populations of Drosophila melanogaster that were previously inbred by single brother/sister matings for over 150 generations. Mutational meltdown did not occur in small populations (Ne = 2 to 4). Only one line went extinct out of 52 tested lines. In fact, there were significant increases in average progeny sizes over time that had to be caused by new beneficial mutations.