Table 2 The speed of Muller’s ratchet under obligate asexuality, assuming fixed population size N = 10^{3} individuals and deleterious mutation rate U = 1.116. n_{0} = Number of individuals within the least-loaded class, s = selection coefficient, t_{(J)} = interclick time estimate based on Eq. 34 in [28], t_{(NS)} = interclick time estimate based on Eq. 33 in [29] and t_{(ME)} = interclick time estimate based on Eq. 24 [30]; all time estimates are given as numbers of generations per “click”. Bold text = estimates of the selection coefficients of the fastest ratchets; the (J)-value was computed according to Eq. 34 in [28], corresponding to a U-shaped function with a local minimum at s = 0.212, which we considered as a critical value of the fastest ratchet acting on sporophytes