The evolution of senescence under curtailed life span in laboratory populations of Musca domestica (the housefly)

The evolution of senescence may be explained by two different, but not mutu ally exclusive, genetic mechanisms. The antagonistic pleiotropy hypothesis predicts that senescence is a consequence of the fixation of alleles with p leiotropic effects favouring early life fitness, but bearing a cost in late r life. The mutation-accumulation hypothesis attributes senescence to the a ccumulation of deleterious mutations with late-acting effects on fitness in mutation-selection balance. Experiments were carried out on the housefly, Musca domestica, in which large and small populations were maintained so th at reproduction was limited to four or five days after reaching sexual matu rity. Longevity declined significantly under the husbandry protocol and was largely the same in large and small populations; this is consistent with t he random accumulation of deleterious alleles affecting longevity under cur tailed life span, although laboratory adaptation cannot be ruled out entire ly as a causal mechanism. An analysis of life-history data did not provide evidence for a trade-off between longevity and age at sexual maturity, deve lopmental time, or dry body weight, but there was an apparent trade-off bet ween longevity and early progeny production, in support of antagonistic ple iotropy.