ABSTRACT
Dietary choice in relation to some biological characteristics of Drosophila melanogaster (Miegen, 1830) (Diptera, Drosophilidae) in Samaru Zaria, were investigated. Sixty Drosophila melanogaster used for the experiment were identified morphologically using the hand lens, dissecting and light microscope. The fruit flies were left to select a diet of Banana, Orange and Pineapple and some number of combinations based on ratios 1:1 and 2:1. The number of Drosophila melanogaster found on each diet were observed and counted. The diet introduced to the fruit flies was covered with a fine mesh cloth and left to breed. The numbers of progenies found on each substrate was observed and recorded. The fecundity of fruit flies found on each of the substrate was estimated based on the number of progenies that emerged. From the result obtained, Banana food substrates recorded the highest preference (8.67) P>0.05 which was the most preferred fruit diet. Followed by Pineapple fruit substrates (6.00) and Orange food substrate with (3.67) which was the lowest, combination of food substrate based on equal proportion (1:1) indicates that Banana-Pineapple combination (7.33) was the most preferred diet amongst the various combinations. The (2:1) combination indicates that Banana-Pineapple (8.00) was the most preferred diet. Banana fruit diet recorded the highest number of progeny with (18.00). Pineapple fruit substrates (10.33) did not differ significantly (P>0.05). Orange fruit substrates recorded (9.67). The average progeny observed in each individual fruit substrates was (12.67) which was higher than Orange-Pineapple but lower than Banana fruit substrates. Similar trend was observed in various combinations based on ratios 1:1 and 2:1.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the study
Drosophila melanogaster Meigen,1830 (Order :Diptera, Family: Drosophilidae) is a fruit fly that is approximately 3mm long being used as the model organism for research in genetics. The knowledge of the complete genome makes it easy to conduct experiments and research with these flies that have a comparatively short life cycle and are easily cultured. Like many insects, the Drosophila life cycle involves complete metamorphosis, in which there is distinct larva, pupal and adult stages. The female Drosophila lays its eggs, each approximately half a millimeter in length after a day of fertilization, the embryo is formed into larva then consumes food and therefore grows in a continuous manner for nine days (Manning, 2006).Drosophila depends on hair like structure called sensilla located on multiple parts of their body including the proboscis, legs and ovipositor. Each of these receptors contains 68 gustatory receptors that helpDrosophilato select Food nutrients and mates.They prefer food with High sugar content and salt content (Montell, 2009). The proboscis ofDrosophila is made up of internal and external sensilla, the external sensilla detect preferable food sources and the internal sensilla check the food before it is allowed into the digestive system. There are also the sensilla located on the ovipositor, which is used by the females to identify oviposition sites. Males on the other hand have more sensilla on their forelegs to allow them to sense pheromone levels when choosing a mate. The taste sensing neurons in the receptors are called bona fide neurons which are similar to the neurepithelial neurons found in the tastebuds of mammals. The readings from the sensilla are absorbed and transmitted to the sub esophageal ganglion region of the brain where it is then processed (Montell, 2009). These sensilla are subdivided into categories that classify them in
terms of length and function in terms of length they are separated into long (l–type), intermediate (i–type), and a short (s-type). Then another subdivision separated them by function into cells focused on fourGustatory Receptor Neurons (GRNs) in the response to sugars (s cell), water (w cell), and low concentrations of salt (L1), and high concentrations of salt (L2). These different types of sensilla act as taste buds for the Drosophila in search for nutritious food (Montell, 2009).
All insects including Drosophila have a natural ability to evaluate their nutrient requirements based on the supply from environment and translate this information into behavioural responses;there is little knowledge of this regulatory underlying mechanism that does these induced modifications (Shiraiwa and Carlson, 2007). Most animals prefer a particular food or drink based on the taste. Therefore it is very efficient to form a memory lasting for days in Drosophila with a single two minimum pairing of odorant and sucrose (Ryudaet al., 2008). Sweet taste can be an undependable indicator of nutrient value because some sugars such as sucrose and fructose cannot be metabolized. The issue is that these sugars are both detected by the same gustatory sensory in Drosophila therefore making it difficult to distinguish between sugars.Nutritious food generate quick and healthy memories, it is possible to train this Drosophila to prefer more nutritious sugar (Burke and Waddell, 2011). Drosophila primarily sense sugars using Gustatory Receptor Neurons (GRNs) located on tarsae and mouthparts. Contact through the tarsae of desirable sugars drives proboscis extension, while stimulation of gustatory neurons on the labellum promotes food acceptance and then ingestion (Burke and Waddell, 2011). It is a well-known fact that when there is an availability of food, there will be an increase in population of any vertebrate animal and it is no different in Drosophila (Elland, 2006).
For egg-laying insects, selecting the best site to lay eggs is crucial for the survival of the eggs and larvae. Once the eggs have been deposited, the maternal care of the female flies‟ ends: the eggs and larvae are henceforth at the mercy of their environment; their range is usually limited so suitable and sufficient food sources for the hungry larvae and protection against predators and parasites are important selection criteria for the best oviposition substrates (Elland, 2006).
The complex nutritional environment of growing, developing animals contributes to shaping an equally complex suite of life history characters, such as survival, developmental time, final body size and shape, longevity, and fecundity (Simpson and Raubenheimer, 2012). Yeasts are known to play an important role in nutrition physiology and host attraction of many Drosophila species. Among other saprophagousDrosophila species, Drosophila melanogaster shows high attraction to Saccharomyces cerevisiaefor oviposition. Studies on the nutritional importance of dietary yeast on Drosophila melanogaster show an explicit influence of different yeast species to larval and adult fitness traits (Anagnostouet al., 2010). Additionally, it was found that larvae and adults of D. melanogaster prefer specific yeast species. However, these preferences vary between adult and immature Drosophila stages (Anagnostouet al., 2010). Specific effects of single yeast species however may be less important, considering the findings of Rholfsand Kürschner (2010). Their findings suggest favourable effects of an increased species diversity and appropriate species combination of dietary yeast on DMelanogaster
Figure1.1: Drosophila melanogaster Life Cycle, the Drosophila develops through the first instar larva, second instar larva, third instar larva, and pupa stage to mature into an adult fly (Elland, 2006)
The biological characteristics which involve the mechanism of deciding or changing food preferences in Drosophila melanogaster is not fully documented (Fougeronet al., 2011). Information on the choice of food in Drosophila melanogaster and how it affects the growth and development in the natural population is limited in Zaria
1.3 Justification of the Study
The knowledge on the types of food and their effects on the biology of the Drosophila will shade light on the nutritional requirements for Drosophila melanogaster.
The information on nutrition that shapes the life history character and the detailed relationships between diet, nutrient intake, lifespan and reproduction in Drosophila melanogaster (Lee, 2007)
1.4 Aims and Objectives of the Study
The Aim of the Study is to evaluate the natural choice of food requirement of
Drosophila melanogasterwhile the Objectives of the Study are as Follows:
To determine the choice of food based on theprotein-carbohydrate ratios in Drosophila melanogaster population diet.
To determine the effects of the food chosen on the fecundity of Drosophila melanogaster.
To determine the effect of food choices on Drosophila melanogaster larval development.
There is no significant difference in the choice of food in Drosophila melanogaster population based on the protein-carbohydrate ratio.
There is no effect of the food chosen on the fecundity of Drosophila melanogaster.
There is no significant difference on the effect of food choices on Drosophila melanogaster larval development time.
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