DOI: 10.5061/dryad.mcvdnck21
title: Maternal and paternal sugar consumption interact to modify offspring life history and physiology

description: Intergenerational effects on offspring phenotypes occur in response to
 variation in both maternal and paternal nutrition. Because the combined
 maternal and paternal effects are rarely considered together however,
 their relative contributions, and the capacity for interactions between
 parental diets to shape offspring life history and physiology are not
 understood. To address this, we altered sucrose levels of adult fruit
 flies (Drosophila melanogaster) prior to mating, across two generations,
 producing parent-parent and parent-offspring combinations that were either
 matched or mismatched in dietary sucrose. We then measured lifespan,
 fecundity, body mass, and triglyceride levels in parents and offspring. We
 reveal complex non-additive interactions, that involve diets of each
 parent and offspring to shape offspring phenotypes, but the effects were
 generally not consistent with an adaptive response to parental diet.
 Notably, we find that interacting parental flies (sires and dams) lived
 longer when their sucrose treatments were matched, but they produced
 shorter-lived offspring.
description: Male and female virgin
 flies were assigned to one of the two dietary treatments prior to mating
 (we refer to this generation of flies as F0), and then the offspring
 produced (we refer to this as the F1 generation) were also assigned to one
 of the two treatments. All possible combinations of dam × sire × offspring
 diet treatment were represented (= 2 × 2 × 2 = 8 combinations).
 Specifically, we collected flies of the F0 generation as virgins and
 placed them in vials of 10 flies across 30 vial replicates per treatment
 (1300 flies, 650 of each sex), in their respective sexes, onto either the
 high sucrose (20%) or the low sucrose (2.5%) diets for the first 6 days of
 their adult life. We transferred flies to vials containing fresh food of
 the designated diet every 48 hours during this 6 day period.
 At day 6, we randomly
 sampled six vials from each treatment, and snap froze (using liquid
 nitrogen) the flies of these vials, storing them at -80°C for later
 triglyceride and body-weight assays. Cohorts of flies in the remaining
 vials then entered a cohabitation phase to enable female and male flies to
 mate. Cohorts of males and female flies were combined, in vials of 10
 pairs, in each of all four possible diet combinations: Lower sucrose
 females × lower sucrose males; higher sucrose females × higher sucrose
 males; lower sucrose females × higher sucrose males; higher sucrose
 females × lower sucrose males. During this phase, flies cohabited for 96
 hours, allowing them to mate. They were transferred to a new vial with
 fresh food of standard 5% sucrose diet every 24 hours during this
 time. Following the cohabitation
 phase of 96 h, the F0 flies were separated back into their respective
 sex-specific cohorts, and placed back onto the high or low sucrose diets
 that they were originally assigned prior to the cohabitation phase, in
 vials of 20 flies. Flies of these vials were then monitored for longevity
 (the longevity assay is described below). The vials from the 6 day old F0
 flies (i.e., the vials from day 1 of the 96 h cohabitation phase) were
 retained, and the eggs that had been laid by females of the respective
 vials were trimmed to 80 per vial (by removing excess eggs with a
 spatula). The remaining eggs were left to develop into adult offspring
 over 10 days at 25°C (on a 12:12 light/dark cycle in a
 temperature-controlled cabinet; Panasonic MLR-352H-PE incubator). These
 adult flies constituted the F1 offspring in the experiment, all F1 were
 reared on standard media (5% sucrose). We collected virgin F1 adults from
 each of the four combinations of parental diet treatments, and placed them
 in their respective sexes in vials of 10 flies, across 30 vial replicates
 per treatment per sex (2400 flies). We then assigned these F1 flies,
 produced by each dietary treatment combination of F0 flies, to either the
 lower sucrose or higher sucrose diet. At day 6 of adulthood, we snap froze
 F1 flies of six randomly chosen vials per dam × sire × offspring diet
 combination. On the same day, 10 virgin focal F1 flies were placed
 together with 10 <em>tester</em> flies of the opposite sex
 (age standardised), collected from the Dahomey stock population, entering
 into a cohabitation phase of 96 h (during which time the number of eggs
 laid by females of each vial was assessed). After 96 hours flies were
 separated again into their respective sexes (in vials of 20 flies), and
 assigned back onto either the lower sucrose or higher sucrose diets that
 they had been on prior to cohabitation, and a longevity assay carried
 out.