Ps. Miller et Pw. Hedrick, Purging of inbreeding depression and fitness decline in bottlenecked populations of Drosophila melanogaster, J EVOL BIOL, 14(4), 2001, pp. 595-601
Drastic reductions in population size, or bottlenecks, are thought to signi
ficantly erode genetic variability and reduce fitness. However, it has been
suggested that a population can be purged of the genetic load responsible
for reduced fitness when subjected to bottlenecks. To investigate this phen
omenon, we put a number of Drosophila melanogaster isofemale lines known to
differ in inbreeding depression through four 'founder-flush' bottleneck cy
cles with flush sizes of 5 or 100 pairs and assayed for relative fitness (s
ingle-pair productivity) after each cycle. Following the founder-flush phas
e, the isofemale lines, with a large flush size and a history of inbreeding
depression, recovered most of the fitness lost from early inbreeding, cons
istent with purging. The same isofemale lines, with a small flush size, did
not regain fitness, consistent with the greater effect of genetic drift in
these isofemale lines. On the other hand, the isofemale lines that did not
show initial inbreeding depression declined in fitness after repeated bott
lenecks, independent of the flush size. These results suggest that the natu
re of genetic variation in fitness may greatly influence the way in which p
opulations respond to bottlenecks and that stochastic processes play an imp
ortant role. Consequently, an attempt intentionally to purge a population o
f detrimental variation through inbreeding appears to be a risky strategy,
particularly in the genetic management of endangered species.