Selection under assortative mating in mice

Abstract

1. Approximately 25000 mice have been produced over twelve generations of selection in nine lines. The experimental design involved a 3 × 3 factorial arrangement of direction of selection with mating system. The primary character measured was 6-week body weight.2. Consistently high phenotypic correlations between mates have been achieved, positive in the assortative lines, negative in the disassortative lines. Correlations were low and inconsistent in direction in the random-bred lines. These correlations have had very little, if any, effect in redistributing the genetic variance as estimated from the variance component analysis; the expected higher variances in the assortative lines and expected lower variances in the disassortative lines have not appeared, thus leaving heritability unaffected.3. Selection differentials likewise show no consistent advantage for the assortative lines, so that the progress from selection has been virtually identical in all three mating systems in each direction.4. Assortment of mates, either positively or negatively, for characters of even moderate heritability appears to have little influence on the outcome of selection. On the other hand, selection has been singularly effective in modifying the mean 6-week weight, with progress markedly greater in the downward direction; indeed it appears that the lower limit, may already have been approximately attained.5. Environmental effects operating in the various generations have affected all lines in remarkably consistent fashion.

The effects of assortative mating on the genetic change due to linear index selection in Tribolium

“…W ilson et al (1968) found no indication that assortative mating increases selection response for larval weight in Tribolium. S utherland et al (1968) used both assortative and random mating to select for 6‐week body weight in mice; the progress from selection was identical in both mating systems. B aker (1973) studied a single‐generation situation and found that assortative mating could increase response to selection but not by more than 10% in most situations.…”

“…Few experiments have checked the usefulness of positive assortative matings as a method of increasing selection response, and the experiments to date have been carried out in situations that only consider direct selection for a single trait (M c B ride and R obertson 1963; W ilson et al 1965, 1968; S utherland et al 1968). The effects of assortative mating in relation to selection for linear indices are not known from previous experimental and theoretical work.…”

Short-term Changes in the Variance: 1. Changes in the Additive Variance

“…Studies in both Drosophila melanogaster (McBride and Robertson 1963) and Trobolium castaneum (Wilson et al 1965;Garcia Gil 1993, 1994) observed slight (but not statistically significant) increases in response when parents were assortatively mated. Conversely, Sutherland et al (1968) and Garcia and Sanchez (1992) found no effect of assortative mating when selecting on body weight in mice and Drosophila pupal weight (respectively). Jorjani (1995) suggested that the combination of both a small expected increase coupled with unconscious assortative mating in the presumed random-mating controls accounts for this lack of consistency.…”

A note on the use of assortative mating in tandem selection

“…McBride and Robertson (1963) with Drosophila melanogaster, Wilson, Kyle and Bell (1965) with Tribolium castaneum and Sutherland, Biondini and Haverland (1968) working with mice evaluated experimentally the joint effect of mating systems and selection and reported, except in the last study, advantages in assortatively-mated lines compared with randomly-mated controls although the differences were not significant. McBride and Robertson (1963) with Drosophila melanogaster, Wilson, Kyle and Bell (1965) with Tribolium castaneum and Sutherland, Biondini and Haverland (1968) working with mice evaluated experimentally the joint effect of mating systems and selection and reported, except in the last study, advantages in assortatively-mated lines compared with randomly-mated controls although the differences were not significant.…”