Genetic and Sex-Specific Transgenerational Effects of a High Fat Diet in Drosophila melanogaster

Abstract

An organism's phenotype is the product of its environment and genotype, but an ancestor's environment can also be a contributing factor. The recent increase in caloric intake and decrease in physical activity of developed nations' populations is contributing to deteriorating health and making the study of the longer term impacts of a changing lifestyle a priority. The dietary habits of ancestors have been shown to affect phenotype in several organisms, including humans, mice, and the fruit fly. Whether the ancestral dietary effect is purely environmental or if there is a genetic interaction with the environment passed down for multiple generations, has not been determined previously. Here we used the fruit fly, Drosophila melanogaster, to investigate the genetic, sex-specific, and environmental effects of a high fat diet for three generations' on pupal body weights across ten genotypes. We also tested for genotype-specific transgenerational effects on metabolic pools and egg size across three genotypes. We showed that there were substantial differences in transgenerational responses to ancestral diet between genotypes and sexes through both first and second descendant generations. Additionally, there were differences in phenotypes between maternally and paternally inherited dietary effects. We also found a treated organism's reaction to a high fat diet was not a consistent predictor of its untreated descendants' phenotype. The implication of these results is that, given our interest in understanding and preventing metabolic diseases like obesity, we need to consider the contribution of ancestral environmental experiences. However, we need to be cautious when drawing population-level generalization from small studies because transgenerational effects are likely to exhibit substantial sex and genotype specificity.

Fig 1. Crossing schematic.

In the first generation (P), larvae were fed a normal diet (Control) and a high fat diet (High Fat). P adults within each genetic line were crossed to create three treatment groups for the second generation (F₁). The Control treatment consisted of both males and females from P:Control. F₁:MA were offspring from P:Control males and P:High Fat females. F₁:PA contained offspring from P:Control females and P:High Fat males. F₁ adults were mated to individuals from the same treatment group to create the third generation (F₂). All F₁ and F₂ larvae were reared on a normal diet.

Fig 2. Weight 10 Line Study Data.

Polka dots indicate treatment is significantly different from Control. Black border indicates treatments are significantly different from each other. Multiple testing was corrected using false discovery rate of 0.05.

Fig 3. Substantial variance due to treatment effects in F₁ and F₂ generations in the partition of variance effects for pupal weight phenotypes.

The total explained variance is graphed for females (A) and males (B). The 10 line study is the left most column in each graph while the fall and spring replicates of the 4 line study are the middle and right columns respectively. Variance components are indicated as genotype (periwinkle), generation (green), and generation-by-genotype interaction (fuchsia), while the treatment effects (treatment and all its interactions) are indicated with brackets. The treatment-related effects are enlarged in C (females) and D (males). Variance components of treatment-related effects are indicated as main treatment (aqua), treatment-by-genotype (red), treatment-by-generation (yellow), and treatment-by-genotype-by-generation (blue). The main effect of treatment and its interactions with genotype and generation explain between 5 and 20% of the total variance in the weight phenotype. Relative effect sizes of treatment and treatment-by-genotype-by-generation were consistent across studies in the males but showed more variation in females. The spring replicate of the 4 line study showed reduced total treatment variance effects than observed in the 10 line study, and the fall replicate of the 4 line study, a subset of the 10 line study.

Fig 4. F₁ and F₂ generations' distribution of p-values for ANOVA effects with support significance of treatment effects.

Arrows indicate actual p-values. Distributions based on 1024 permutations across treatments and generations (and replicate for the 4 line study) within genotype and sex to randomize treatment effects. Genotype and sex distributions not shown since they remain highly significant under the permutation model as expected. A-H are derived from the 10 line study while I-P are derived from the Fall and Spring replicates of the 4 line study. Note that all real p-values fall in or beyond the extreme tail of the permutation distribution. Additional ANOVA effect permutations can be found in Figs A and B in S1 Information.

Fig 5. Significant correlation between the Fall and Spring replicates of the 4 line study.

The overall correlation of the actual measurements for all three generations across four genetic lines and three treatments and two sexes showed robust correlation (A). The difference between the average control and treated measurements, across replicates within genotype/sex/generation combinations, also shows a significant positive correlation. (B). When the F₂ data points are isolated from the total set in (B), the correlation is stronger and significant (C).

Fig 6. Reaction norms for pupal weight in the F₂ generation.

The left panels indicate the 10 reaction norms across the three treatments for female pupal weight (A) and male pupal weight (C). The right panels indicates the subset of four genetic lines from the original 10 in the Fall and their Spring replicates for female (B) and male (D) pupal weight, bold indicates the reaction norm from the Spring replicate. For most genetic lines, the reaction norms across the two time replicates in panels B and D maintained a similar pattern.

Fig 7. Difference in egg size of Maternal Ancestor (MA) and Paternal Ancestor (PA) compared to the Control in the 3 line study.

Substantial differences by sex, genotype, and generation were observed for the influence of the high fat treatment. Significance values indicated as p < 0.05 *, p < 0.01 **.