Developmental study of mercury effects on the fruit fly (Drosophila melanogaster)

Abstract

Environmental pollution caused by heavy metals such as mercury is one of the most important human problems. It might have severe teratogenic effects on embryonic development. Some pharmacological and physiological aspects of fruit flies (Drosophila melanogaster) are similar to humans. So the stages of egg to adult fruit fly, as a developmental model, were employed in the study. Wild adult insects were maintained in glass dishes containing standard medium at 25 °C in complete darkness. Five pairs of 3-day old flies were then transferred to standard culture dishes containing different concentrations of mercury ion. They were removed after 8 hours. We considered the following: The rate of larvae becoming pupae and pupae to adults; the time required for the development; the hatching rate in the second generation without mercury in the culture; the morphometric changes during development in both length and width of the eggs through two generations; larvae, pupae and adult thorax length and width. The results showed that mercury in culture (20-100 mg/l) increase the duration of larvae (p<0.01) and pupae (p<0.01) development, the rate of larvae becoming pupae (p<0.001); pupae maturation (p<0.05), the hatching rate (p<0.01), the length (p<0.05) and width of larvae (p<0.01) and pupae (p<0.001) and the length in the adult thorax (p<0.01) decreased significantly. There was no effect upon the size of eggs. There were also no larvae hatching in concentrations of 200 mg/l of mercury. Negative effects of mercury as a heavy metal are possibly due to the interference of this metal in cellular signaling pathways, such as: Notch signaling and protein synthesis during the period of development. Since it bonds chemically with the sulfur hydride groups of proteins, it causes damage to the cell membrane and decreases the amount of RNA. This is the cause of failure of many enzyme mechanisms.

Keywords: fruit fly; hatching; larvae; mercury; pupae.

Figure 1

Comparing the mean length (A) and width (B) in larvae at different concentrations of mercury ions during larval growth. In concentration of 50 mg/l, 80 mg/l and 100 mg/l a delay is indicated during the larval sampling in the presence of mercury ions in the medium. Except for the delay, the transverse and longitudinal growth is declining and eventually their growth has not reached its maximum.For the length (F(6,32)=18.203, and p<0.001) and the width of larvae (F(6,30)=20.289 and p<0.001). The data were presented as mean±SEM (number of larvae n=7 and number of pairs of flies n=20).

Figure 2

Comparison of the mean of length (A) and width (B) in pupae at different concentrations of mercury. Following the high concentrations of mercury ions (80 and 100 mg/l), a significant decrease in mean length and width of the pupae was observed compared with the control (***p<0.001). The results were presented as mean±SEM (number of pupae, n=7).

Figure 3

The average size of the adult female at different concentrations of mercury. Following the high concentrations of mercury ions, a significant decrease in mean length of the adult female was observed compared with the control (**p<0.01 and ***p<0.001). The results were presented as mean±SEM (number of adults, n=7).

Figure 4

Comparison the length (A) and width (B) of eggs of insects which spent their embryonic and maturation periods in the culture medium containing mercury ions with the eggs of insects where only adults were exposed to the mercury ions. No effect on the length and width of the eggs is evident in both cases. The results were presented as mean±SEM (number of egg n=7).