Academics

Abstract

Developmental timing and female fertility are dependent on a wide variety of factors.  Before female flies can allocate resources to reproduction, they must account for the risk-benefit ratio. It is known that changing protein levels in fly food, among other manipulations, affects female fertility and developmental timing. However, the influence due to only manipulating yeast levels is not fully characterized. We evaluated the impact of decreased yeast concentration on the fertility and developmental timing in Drosophila melanogaster. We also tested if there was a difference in the effect of yeast concentration on the fertility and developmental timing of differently aged flies. We found that the yeast concentration played a significant role in decreasing female fertility and increasing developmental timing regardless of age, though age had a negative effect on its own.

Introduction

The strength and survival of animals is dependent on their diet. Thus, altering the diet of an animal will lead to visible as well as cellular differences in animals (Grangeteau et al. 2018). There are multiple ways to test the effect of food on the health of an animal. One such measure is through female fertility and developmental timing. Fertility refers to the ability for the female to produce offspring. Developmental timing refers to the timeframe in which the offspring reach certain measurable changes during their development. In order to test for these parameters, it is helpful to choose an animal with a short lifespan and early maturity. One such model organism is Drosophila melanogaster. Drosophila is a common model organism and one that is relatively easy to take care of in the lab. Drosophila is one of the most used model organisms, not only because of the low cost, short lifespan, and well-documented genetics, but also because most of the genes present in Drosophila are homologous to those in humans (Tolwinski 2017). 

There are multiple possibilities that could be explored when experimenting on the effect of food on Drosophila, but for this experiment, we only chose to test the effect of decreased yeast concentrations on fertility and developmental timing. We chose to test yeast because it is the protein source for the flies. Proteins are known to be important for development, and previous studies have shown that decreasing the yeast concentration emulates overcrowding and has similar effects on the flies during larval development (Klepsatel et al. 2018). Overcrowding is when there are too many flies present and so the availability of nutrients is depleted. Larval crowding has been shown to affect multiple aspects of fly development, including decreased body size, an extended life span, lower fecundity, etc. (Klepsatel et al. 2018). Thus, decreasing yeast concentration will likely lead to smaller flies and other physical changes. 

Food and access to adequate nutrients are also important aspects for mating. Mating is not necessary for survival but is necessary for reproduction, therefore it is an action that can be put off in times when survival is not guaranteed or when nutrients are low. Mating has been shown to take a toll on female fly health, and so the female flies need high nutritional food in order for the benefits of mating to outweigh the risks (Gorter et al. 2016). This indicates that a decrease in the food quality will lead to a decrease in the amount of female mating. Decreased mating will directly influence the measured fertility of the female. Protein rich environments have been shown to lead to higher levels of mating which is associated with the levels of offspring produced (Gorter et al. 2016). In addition, the percentage of protein present in the environment affects the development of larva (Gorter et al. 2016; Grangeteau et al. 2018). Therefore, there are previous studies that support testing the effect of yeast concentration on female fertility and developmental timing (Good and Tatar 2001). For our experiment, we measured female fertility by the number of eggs laid over a certain timeframe and we measured developmental timing by counting the number of flies that eclose over a series of days. Eclosion is the process when an adult fly emerges from the pupal casing. This is a physical change that is easily seen. More information on how fertility and developmental timing were measured will be provided later in the paper.

Since there are common recipes to make food for Drosophila kept in the lab, we decided that we would keep the control group with the usual concentration of 4% yeast. In order to change the yeast concentration enough to have an effect, we halved the concentration of yeast in the experimental group down to 2% yeast. Since the concentration of the control is already relatively low, we hoped that a change of 2% yeast would be large enough, especially since we did not want to remove all yeast from the food source. As mentioned before, previous literature shows a preexisting connection between yeast concentration and the health and fertility of Drosophila, however further characterization is always necessary. Therefore, we hypothesize that if the yeast concentration in the Drosophila food source is halved, then there will be a negative impact on the fertility and development of the flies. To test this hypothesis, we manipulated both the yeast concentration as well as the time frame in which the flies were mated, five-day and twenty-day old female virgins, our “young” and “old” flies respectively. We tested both young and old flies to see if the effect of yeast stayed the same throughout the lifespan or if the effect was confounded in older flies.

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