Quantitative analysis of mating behavior in aging male Drosophila melanogaster.

Dynamic changes in quantitative aspects of mating behavior of the male fruit fly as its life unfolds, from eclosion through maturity (peak performance) and "physiological death" (loss of fertility followed by complete loss of ability to mate), towards actual death, have been identified in this work by observations and measurements on 28 male fruit flies of the Oregon R strain studied individually. At weekly sessions from the first day of their imaginal life until their natural death, each fly was given the opportunity to mate with up to three virgin females during a one-hour period. Length of the latency period of each accomplished mating and duration of copulation were recorded. After mating the females were allowed to lay eggs for 24 hours and the number of offspring was counted 26 days later. The period between 1 and 4 weeks of age is characterized by peak and fairly constant performance: multiple matings, short latencies, long durations of copulation, and high degree of fertility (number of offspring); then a decline sets in, in some measures slower than in others, as the flies age. Large intra- and inter-individual variabilities were, however, found which obscure possible correlations between individual measures of mating ability and length of life. At the individual level, a preliminary analysis showed a good correlation (r = 0.80 and 0.79) between life span and week of last mating (onset of impotence) or week of last fertile mating (onset of sterility). At the population level it was found that a number of measures, i.e. number of remaining maters at each age, number of remaining fertile maters and total number of matings, had an age-course similar to survivorship but anticipated it by 4--6 weeks. Other measures, such as number of multiple matings and number of offspring declined with age faster than survivorship.