Albinism and phenotype of barn swallows (Hirundo rustica) from Chernobyl

The effects of mutation on phenotypic expression are supposed to be mainly deleterious because mutations disrupt the expression of genes that function relatively well under current environmental conditions. Thus, mutations ar e assumed to give rise to deviant phenotypes that are generally selected ag ainst. Radioactive contamination in the Chernobyl region of Ukraine is asso ciated with a significant increase by a factor two to 10 in mutation rate i n microsatellite markers of the barn swallow, Hirundo rustica. Barn swallow s from Chernobyl had a temporally constant, elevated frequency of partial a lbinism compared to the situation before radioactive contamination and comp ared to birds from a control area. Albinism disproportionately affected the carotenoid-based plumage of the head, suggesting that carotenoid metabolis m is particularly susceptible to the effects of radiation. Individuals with partially albinistic plumage had, on average, lower mean phenotypic values than other birds, and this was particularly the case for males. Furthermor e, differences in phenotypic variation, as determined using Levene's test, were significantly larger in partial albinos compared to nonalbinos in male s, but not in females, even though the null expectation would be the opposi te due to the lower mean phenotypic values of partial albinos. Although sma ll phenotypes were commonly associated with germline mutations, there was n o general decrease in overall body size during the period 1991-2000, implyi ng that small individuals were selected against. Because partial albinism i s disfavored by natural selection, the effects of mutations are deleterious , giving rise to a balance between mutation and selection.