Title

Linkage Analysis of Caffeine Resistance and Circadian Rhythm in Caffeine-Treated DDT Resistant and Susceptible Strains of Drosophila melanogaster

Date of Award

8-2007

Degree Type

Thesis

Degree Name

Master of Science

Major

Biochemistry and Cellular and Molecular Biology

Major Professor

Ranjan Ganguly

Committee Members

Jae H. Park, Mariano Labrador

Abstract

Caffeine is found in coffee, tea, soft drinks, many plant products and various drug preparations. It is the most consumed common psychoactive drug around the world. Consumption of caffeine causes several behavioral and physiological responses in humans and other mammals. Caffeine is also known to be an insect repellant and can be used as an insecticide. As observed in mammals, caffeine treatment increases the locomotor activity in insects including Drosophila. However, very little is known about genetic and molecular basis of caffeine sensitivity and action in insects. In the present study, I have used DDT resistant (91-R) and susceptible (91-C and ry506) strains of Drosophila melanogaster to examine whether these strains also differ in caffeine resistance and locomotor activity following caffeine treatment. Results showed that time required for 50% mortality (LT-50) of the 91-R strain were at least 2-fold higher than the LT-50 of the 91-C and ry506 strains. In all strains, caffeine LT-50 was found to be at least 1.5-fold higher in females than in males. I also used chromosome substitution stocks made between the DDT resistant 91-R and DDT susceptible 91-C and ry506 strains. Caffeine-mortality tests on these stocks showed that the major resistance factors against caffeine are linked to the second chromosome and the factors on the X and the third chromosomes play a minor but positive role. Experiments on locomotor activity showed that on caffeine-free media both DDT resistant and susceptible strains were more active during light than dark cycle. While the both DDT susceptible strains showed increased locomotor activity on caffeine media during dark and light cycle, the DDT resistant 91-R strain did not show any change in locomotor activity on medium containing low dose (1.5mM) caffeine. This refractoriness to low dose of caffeine appears to be linked to the second chromosome as deduced by examining the chromosome substitution stocks; strains carrying the second chromosome of 91-R displayed this behavior. On the other hand, locomotor activity of the DDT resistant strain decreased both during light and dark cycle when exposed to higher dose (3mM) of caffeine. This behavior is again found to be linked to the second chromosome because chromosome substitution stocks carrying the second chromosome of the 91-R strain showed decrease in locomotor activity on medium containing 3mM caffeine. The X and 3rd chromosomes also carry factors that modulate the effect of the second chromosome, but in a complex manner.

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