An extreme test of mutational meltdown shows mutational firm up instead

Abstract

Traditionally, the accumulation of new deleterious mutations in populations or species in low numbers is expected to lead to a reduction in fitness and mutational meltdown, but in this study the opposite was observed. Beginning with a highly inbred populations of Drosophila melanogaster, new mutations that accumulated in experiments of two females and two males or of one female and one male each generation for 52 generations did not cause a decline in progeny numbers over time. Only two lines went extinct among 52 tested lines. In three of four experiments there was a significant increase in progeny numbers over time (mutational firm up), which had to be due to new beneficial, compensatory, overdominant, or back mutations.

Two sides of the same coin: A population genetics perspective on lethal mutagenesis and mutational meltdown

“…In other words, this literature has focused on experiments directly modulating either effective population size or mutation rate. It is additionally of note that several empirical papers claiming to study mutational meltdown do not observe extinction of their study population (e.g., Rowe and Beebee 2003 ; Shoubridge and Wai 2008 ; Allen et al 2009 ; Willi 2013 ; Woodruff 2013 ), which may partly be owing to a confusion of terminology: the process of Muller’s ratchet and the event of mutational meltdown are sometimes used interchangeably.…”