INNATE CONTROL OF LOCAL SEARCH BEHAVIOR IN THE HOUSE-FLY, MUSCA-DOMESTICA

The genetic basis of variation in local searching behaviour in the house fly, Musca domestica L., was examined by estimating the heritability of locomotory parameters using parent-offspring regressions. Pathways of adult flies were videotaped for 3 min after ingestion of a 1 mul drop of 0.25 M sucrose in a 75 cm diameter circular arena with minimal external cues. Locomotory variables computed from digitized walking pathways, including locomotory rate, turning rates per unit of distance and time, turn bias, number of stops, and stop duration, were significantly heritable, but heritabilities (additive genetic variance divided-by total phenotypic variance) was generally low (<0.25). Phenotypic variance in search parameters increased with time since ingestion of the sucrose drop, but heritabilities were highest when only the first 30 s of the searching bout were examined, and declined as longer periods were considered. Significant genetic correlations among search parameters suggest that many of these characters are influenced pleiotropically by the same genes or closely linked genes. However, some aspects of local search were inherited independently (e.g. stop duration and locomotory rate). The independence of controlling mechanisms was supported by observed differences between genetic and environmental correlations. This genetic independence could enhance the likelihood of appropriate population responses to temporally or spatially changing selective forces.