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Introduction
Selecting food substances and reaching a nutritionally balanced diet is an important challenge for all animals, including humans (Schwarz et al., 2013). Feeding is an essential component of animal behavior and it is related not only to behavioral activities, but to physiological ones as well. To study these processes, fruit flies (Drosophila melanogaster) have traditionally been used as a powerful model. More recently, they have been used to study the neuronal and molecular mechanisms that intervene in the feeding process. Nevertheless, more studies are needed to quantify feeding in these flies (Itskov et al., 2014).
D. melanogaster is an insect which feeds on the fungi of rooting fruit (Thorne et al., 2014). In the food intake of Drosophila, several behavioral elements make a contribution, including foraging, feeding initiation and termination, and food fruit ingestion (Qi et al., 2015). Particularly, in foraging behavior, the central issue is the way how organisms adjust their activities in response to nature and how the resources are distributed (Prokopy and Roitberg, 1984).
In Drosophila melanogaster, the foraging activity is related to the foraging (for) gene. Two behavioral morphologies, rover and sitter, are associated to the natural alleles in that gene. The rover morphology is associated to the forR gene and the sitter to the forS gene; both of them are related the uptake of nutrients (Prokopy and Roitberg, 1984; Kent et al., 2009). Studies with regards to the foraging and feeding behavior in D. melanogaster can help by correlation to humans, since a link between their genes has been found related to feeding behavior.
The aim of this research was to determine the foraging and feeding behavior of fruit flies (D. melanogaster, apterous). The main question is, Do hungry (apterous) fruit flies prefer ayeast solution to a sucrose solution? Furthermore, the null hypothesis established is that there are no significant differences in the feeding preference of D. melanogaster apterous.
Results
At 30 minutes, the group with the highest value of flies (96) was the one where they were not feeding. Yeast and sucrose feeding test show similar quantities of flies, 50 and 42, respectively. These results changed at 60 min. At this moment, flies feeding with sucrose showed the highest value (76) and the values of the ones not feeding and the ones being fed with yeast solution were around 20 individuals (Table 1). Using the chi-squared analysis the p value for the calculated chi-squared (Х2=84.68, for 30 min) and (Х2= 82.88, for 60 min) was p <0.001 (which is the lowest p value on the table for degree of freedom of 3). Thus, the null hypothesis was rejected, since a significant difference was found.
Discussion
An important challenge for all animals is the selection of food and the achievement of a nutritionally balanced diet (Schwarz et al., 2013). Differences were observed for the 2-choice feeding test with yeast solution and sucrose solution. Around 50% of the starved flies did not feed during the first 30 minutes, while the other approximately 50% fed either with yeast or sucrose. This result can be related to the foraging process and the requirement of the organisms to adjust their activities in response to nature (Prokopy and Roitberg, 1984). It can also be related to the feeding initiation (Qi et al., 2015).
At 60 minutes, only 18.6% of the flies did not show any feeding, while around 74% of the flies fed either with yeast or sucrose, being the last one the highest value (58.9%). Previous reports had shown that larvae deprived with either sucrose or protein later feed with the diet providing the missing nutrient (Schwarz et al., 2013). In this experiment, flies initially fed either with sucrose or yeast, but later preferred to feed from sucrose solution.
During the experiment, no preference was found for either both substances. This is contrary to the results of Schwarz et al. (2013), who determined that larvae prefer a balance mixture of yeast and sucrose. This could be related to the age of the fly, since they worked with larvae, while in adults were used this experiment adults. Other investigations on fruit flies have shown that after a period of yeast deprivation, flies prefer yeast over sugar and those deprived on sugar preferred sucrose over yeast (Piper et al., 2014). This can be explained by referring to the fact that initially, at 30 minutes of this experiment, flies chose either yeast or sucrose. Also, there is a probability of running out of some nutrients in yeast and flies search for food in sucrose solution at 60 min. Significant difference (p<0.01) between the expected and observed result for feed treatment demonstrated that some factors other than the aleatory are operating for the deviation.
Differences between the values can be related to some aspects, such as dead flies and faulty observation ability to differentiate between flies. Other experiments can be done to determine the molecular influence in the differences on foraging behavior in fruit flies. Also, increasing the number of flies can bring more accurate results.
References
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Kent C. F., Daskalchuk T.,Cook L.,Sokolowski M. B.and Greenspan R. J. (2009) The Drosophila foraging Gene Mediates Adult Plasticity and Gene–Environment Interactions in Behaviour, Metabolites, and Gene Expression in Response to Food Deprivation. Public Library of Science. DOI: 10.1371/journal.pgen.1000609.
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