Effects of Gamma Radiation on Mating Competitiveness and Behavior of Drosophila melanogaster Males

To determine whether radiation affected the mating behavior, an irradiated or untreated male fly was introduced into a vial containing a single virgin female. All treated male flies were three to four days old when exposed to 8 or 16 kr of gamma radiation from a Co⁶⁰ source delivering about 320 r/min. Untreated males or males exposed to 8 kr showed no difference in courtship time during their first or second matings, either on the same day of treatment or on the day after treatment. Males exposed to 16 kr were slower to mate the first and second times on the day of treatment. However, 24 hr after treatment, males treated with 16 kr had recovered and mated as readily as untreated males or males exposed to 8 kr. The time in copulation was also unaffected by irradiation. Males exposed to 16 kr, when confined with 5 or 10 virgin females, mated fewer times than untreated males during the first 24 hr. Irradiated males confined with 20 virgin females mated less frequently than untreated males confined with 20 virgin females but not less than untreated males confined with 5 or 10 virgin females. However, at the end of three days the irradiated flies confined with 5, 10, or 20 virgin females had mated as many times as untreated males. Thus the delay in number of matings by males irradiated at 16 kr corresponds to the delay in the courtship period recorded in the 1st experiment. The effect of irradiation on competitiveness of males irradiated with 16 kr was determined by confining for a 24-hr period these males and untreated males in 1:1, all ratios, except the 5:1, treated males were as competitive as untreated males. (BBB)