The effect of serial founder-flush cycles on quantitative genetic variation in the housefly

Abstract

Experimental populations of the housefly, initiated from a single outbred natural population, were subjected to five serial founder events of one, four, or 16 pairs of flies. After each bottleneck the populations were allowed to flush to approximately 1000 pairs, at which time they were assayed for additive genetic variance for eight morphometric traits using parental-offspring covariances. Additive genetic variance for all bottleneck sizes rose above the level of the outbred control in response to the first bottleneck and remained comparable to or higher than that of the control over most of the successive bottleneck episodes; no bottleneck size exhibited additive genetic variance significantly below the level of the control throughout the experiment. Such changes in additive genetic variance in response to bottlenecks are inconsistent with a model of neutral additive gene action, suggesting that non-additive components of genetic variance are likely to have affected the traits. Two models of non-additive genetic variance, pure dominance and additive-by-additive epistasis, provided reasonable fits to our data, but were not distinguishable from each other. Both empirical and theoretical results suggest that additive genetic variance for quantitative traits can remain high despite repeated reduction of the population size to as low as a single mated pair. Historical bottlenecks cannot be accurately inferred from levels of additive genetic variance for complex quantitative characters that are affected by non-additive components of genetic variance. © The Genetical Society of Great Britain.