Figure 1

Predicted extinction times of C. elegans based on mutations in the nuclear genome. (A) Analytical results only. (B) Analytical and simulation results combined. The solid, black horizontal line denotes the estimated divergence time of C. elegans relative to its closest known outcrossing relatives (18 Myr), including upper and lower limits (grey lines; the upper limit of about 100 Myr from some older studies is marked separately). Extinction time estimates below this line indicate that extinction by Muller's ratchet is expected to have occurred, under a scenario of pure self-fertilization since divergence from known outcrossing sister taxa. The bar along the bottom labeled N _e s = 1 indicates the boundary for selective neutrality of mutational effects (for the range of N _e given in Table 1). Thick colored lines represent the analytic predictions of the extinction time for different effective deleterious genomic mutation rates (U _sdm ) for N _e = 10 000, T _gen = 60 d, and R _max = 280 offspring/generation. Thin dashed lines demarcate bounds of uncertainty for U _sdm = 0.5, based on upper and lower limits of N _e , T _gen and R _max (Table 1); variability in extinction time is similar for other U _sdm . Large symbols denote valid extinction time estimates from independent simulation runs with two or more observed clicks of Muller's ratchet. Small symbols denote lower limits for extinction times from simulations without observed clicks, assuming that the ratchet would have clicked just after stopping the simulation. This plot contains 36 393 simulations with a total of 19.9 years of computing time. The nearly vertical right portion of the extinction time curves represents the "wall of background selection", indicating that mutations with larger effects are eliminated deterministically.