mutation accumulation

Cutter AD & Payseur BA 2003 Rates of deleterious mutation and the evolution of sex in Caenorhabditis. J Evol Biol 16:812-822.

• deleterious mutations may not have synergistic effects on fitness, on average
• a recent test for synergistic epistasis between mutations affecting C. elegans life-history traits found only a nonsignificant trend for this mode of gene interaction (Peters & Keightley 2000)
• the lack of a dominant role of synergistic interactions also has been shown in Escherichia coli (Elena & Lenski 1997), viruses (Elena & Moya 1999; de la Pena et al. 2000), and Saccharomyces cerevisiae (Wloch et al. 2001)
• although experiments with Chlamydomonas (de Visser et al. 1996) and Drosophila melanogaster (Mukai 1964; Kitagawa 1967) have supported the notion of synergistic epistatic interactions

• ecological conditions in nature could induce epistatic gene interactions that are unobservable in the laboratory (Peters & Keightley 2000)
• the degree of epistasis in the C. briggsae and C. remanei genomes remains unknown