The use of fluctuating asymmetry and phenotypic variability as indicators of developmental instability – testing maternal effect employing clonal organisms

The impact of maternal effects on developmental stability (DS) was investigated in Drosophila mercatorum by measuring fluctuating asymmetry (FA) and phenotypic variability (Vp). Maternal effects are normally difficult to estimate, as both genetic and environmental components affect the phenotype; however, by using a homozygous parthenogenetic strain of D. mercatorum, we could exclude any genetic variance among the individuals. In order to estimate the amount of environmental variance (Venv) in a monoclonal population a new methodology was used. The impact of the maternal environment on FA and Vp for three wing traits was measured in the progeny. This new method has been applied for quantifying the produced "bias" of Venv on FA and Vp and may give insight into why non-reproducible results have been obtained in DS studies so far. The maternal flies were treated in a water bath at different temperatures (36 °C, 37°C, 38°C and 25°C as control temperature). The results showed a tendency towards an increase of FA and Vp for all three traits in the progeny from mothers being stressed at high temperatures. This shows maternal effects for temperature stress resulting in an increased developmental instability (DI) in the offspring of heatstressed mothers.