Random environmental variation and inbreeding: effects on pure-strain and hybrid populations of flour beetles (Tribolium)

Publisher Website
Google Scholar
Abstract
The effect of inbreeding and of random environmental variation on fitness characters was studied in small populations derived from 10 inbred laboratory strains of Tribolium castaneum (1) and in 18 hybrids (IH) populations, obtained by crossing six mutant to three wild-type strains. Replicate population of each type were held in a constant (C) and a randomly varying (V) environment. Each replicate population was founded by a single pair of adults and one pair of sibs founded each subsequent generation. Thus four groups of inbreeding populations were created: IC, IV, IHC, and IHV. Outbred hybrid populations were held in the varying environment (OV). Several fitness characters were measured. The results confirmed that inbreeding populations exposed to random environmental variation had lower fitness than similar populations in the constant environment populations, as expected (IHC > IHV, IC > IV for each fitness trait). The environmental stress did not result in selection for individuals with higher fitness. In the hybrid populations, consistent and significant differences in fitness between populations having different wild-type (female) ancestors persisted for several generations. No such differences were found among populations grouped by their mutant ancestor. Within each environment, inbreeding had a pronounced effect on fitness. The order of magnitude of the fitness characters was IHC > IC, OV > IHV > IV, parallel to the level of inbreeding. Directional changes in relative (rank) magnitude of fitness characters among populations suggested that their genetic composition was changing temporally.