deleterious mutation & geographic structure

Theodorou K & Couvet D 2006 Genetic load in subdivided populations: interactions between the migration rate, the size and the number of subpopulations. Heredity 96:69-78.

in order to investigate the relative importance of the parameters that determine population structure (n, m, N) on the genetic load of the population, we calculated the elasticity of the mean fitness with respect to each of these parameters
we used elasticity, rather than sensitivity, because the parameters under study are measured and managed on different scales

the majority of mutations are slightly deleterious (s = 0.01–0.03) with mutation rates per diploid genome of U = 1 and a mean dominance coefficient of h = 0.2–0.4
the validity of these estimates has been recently questioned
new experimental studies on Drosophila melanogaster and other organisms suggest that mutation rates are much lower, U = 0.01–0.02, and the average effect in fitness higher than previously thought, s = 0.1–0.2 (Bataillon, 2000; Caballero et al, 2002)
other studies report intermediate mutation rates of U ≈ 0.1 (Fry, 2001; Fry and Heinsohn, 2002)
Rodríguez-Ramilo et al (2004) found evidence for both sets of mutation parameters (slightly deleterious – high mutation rate and mildly deleterious – low mutation rate)

most of our analysis considers the mutation set U = 1, s = 0.02 and h = 0.3
since the majority of arguments is in favor of such values (Lynch et al, 1999)
the dependence of our results on the choice of the mutations parameters was also checked

the inclusion of the third moment of allele frequency in the diffusion equations improves significantly the precision of our approximations in the case of slightly deleterious and highly recessive alleles (hs low)

we performed stochastic multilocus simulations in order to check the influence of the number of subpopulations (n) and the effects of linkage disequilibrium on the precision of diffusion approximations

for highly recessive alleles (h = 0.1) fitness is significantly lower after 50 generations of subdivision than at equilibrium
with subdivision, homozygosity increases and the previously masked deleterious alleles are now exposed to selection
during purging, fitness is low and it rebounds only after a considerable number of generations
for m = 0.025, it can take a 100 generations for fitness to recover to levels close to equilibrium (results not shown)
a transient genetic load due to highly recessive alleles was also observed by Kirkpatrick and Jarne (2000) for bottlenecked populations