Heat-induced maternal effects in Drosophila mercatorum and its evolutionary consequences

The impact of temperature-induced maternal effects on offspring phenotypic variability (delta(p)(2)), developmental instability, the interaction between developmental instability and the environmental variability (delta(e)(2)). here called the environmental covariance effect (ECV), and the size of ten wing traits were investigated in a parthenogenetic strain of Drosophila mercatorum. The maternal flies were treated in water-baths at different high temperatures (25 degrees C [control], 36 degrees C. 37 degrees C. 37.5 degrees C and 38 degrees C). The results showed an overall increase in offspring wing traits' delta(p)(2) and ECV with increasing maternal temperature up to 37 degrees C. Above this temperature delta(p)(2) and ECV decreased. and in some cases dropped below the values found for the control temperature. Developmental instability and delta(e)(2) did not show a clear pattern with increasing temperature stress. even within the same trait. The mean size of the offspring wing traits increased with maternal temperature up to 37.5 degrees C, where it reached a plateau. By using a parthenogenetic strain we were able to exclude any genetic contribution to the variation among individuals. The results show that the effect of temperature stress can be maternally transmitted and that it has an impact on offspring size and delta(p)(2). This study is the first to provide a precise quantitative estimate of the maternal effect and its components (delta(p)(2) developmental instability, ECV, delta(e)(2), and mean trait size). The evolutionary consequences of the changes on these components are discussed.