Bugs on Drugs: Paracetamol Exposure Reveals Genotype-Specific Generational Effects on Life History Traits in Drosophila melanogaster

Abstract

Few investigations have been made to determine whether pharmaceutical drugs cause any generational effects. These effects can be divided into intergenerational and transgenerational effects. In insects, the F1 offspring of exposed individuals are considered to show intergenerational effects (as they have been exposed as germ cells or early embryos), while the F2 generation is fully non-exposed and considered to show transgenerational effects. Here, the common over-the-counter (OTC) drug, paracetamol, is investigated for genotype-specific responses and effects across generations on three life-history traits: fecundity, longevity, and spontaneous locomotor activity levels in the model species Drosophila melanogaster. Seven isofemale D. melanogaster lines were exposed to a high and intermediate dose of paracetamol determined by a dose-response curve. NMR investigations verified the long-term presence of paracetamol in the food substrate. Phenotypic effects of paracetamol ingestion were investigated on flies exposed to the drug and in their offspring and grand-offspring. The dose-response curve indicated genotype-specific responses to paracetamol. In the following experiment, all traits investigated displayed significant effects of paracetamol ingestion for at least one of the seven isofemale lines, and we detected strong genotype-specific responses to paracetamol. Fecundity tended to increase in individuals directly exposed to the drug whereas fecundity in the F2 generation was reduced (transgenerational). Longevity generally decreased in directly exposed individuals but tended to increase in F1 offspring (intergenerational). Paracetamol effects on spontaneous locomotor activity were primarily detected as transgenerational effects and were rarely seen in directly exposed individuals. However, across lines, no clear overall trend could be determined for any trait. The generational effects and marked genotype-specific response to paracetamol warrants further investigation of both genotype-specific responses and generational effects in general.

Keywords: epigenetic inheritance; fecundity; genotype by environment; insect model; longevity; personalized medicine; pharmaceutical; precision medicine; spontaneous activity.

Figure 1

Experimental design of Experiment I (top panel) and Experiment II (bottom panel). In experiment I, egg-to-adult viability was investigated in five (isofemale line) or ten (outbred population) replicate vials with 50 eggs each.

Figure 2

Percentage egg-to-adult survival of individuals from an outbred population (n = 10 vials of 50 eggs) or an isofemale line (n = 5 vials of 50 eggs) at different concentrations of paracetamol. Points represent means ± standard error of the mean.

Figure 3

Fecundity of exposed flies (F0) or their offspring across two generations. Bars show the mean of all seven isofemale lines. Error bars show the standard error.

Figure 4

Longevity of exposed flies (F0) or their offspring across two generations. Bars show the mean of all seven isofemale lines. Error bars show standard error.

Figure 5

Spontaneous locomotor activity of exposed flies (F0) or their offspring across two generations. Bars show the mean of all seven isofemale lines. Error bars show the standard error. Hatched bars represent old flies and unhatched bars young flies.

Figure 6

Line-specific responses to paracetamol of seven different isofemale lines (L1–L7) represented in different columns, and for four different phenotypic traits (fecundity, longevity, and young and old spontaneous locomotor activity) represented by rows. Lines show reaction norms to 0, 20, and 40 mM paracetamol exposure in the first (F0) generation. All values are normalized to the F0, 0 mM treatment for all lines for easier comparison of the response to paracetamol. Filled symbols represent significant differences from the associated (same generation) control (red = increased and blue = decreased). For an evaluation of absolute differences between treatments, refer to Figure 3, Figure 4 and Figure 5.