Studies in several species have revealed that changes in reproductive activity result in inverse changes in lifespan. It is interesting to know how this "cost of reproduction" is incurred. Earlier, investigators had shown that mated female fruitflies have significantly shorter lifespan than virgin females. Recently, it has been demonstrated that mated young female fruitflies are significantly more susceptible to oxidative stress and starvation than virgin ones. It is possible that reproductive activity renders organism more vulnerable to various types of stress and that the accumulated damage has a role in the observed decrease in lifespan. To explore the extent of the relation between reproduction and stress susceptibility, we compared mated and virgin young fruitflies for susceptibility to another type of stress, heat stress. Fruitflies were sexed within two hours after eclosion. Half of fruitflies were kept together and were allowed to mate freely. The other half were segregated according to sex and kept in separate bottles for virgin males and virgin females. After five days in standard laboratory conditions, fruitflies were incubated at 40 degrees Centigrade and each individual was closely observed until death. Analysis of survival data revealed that in both sexes mated fruitflies were significantly more susceptible to heat stress than the virgin ones.
Cost of Reproduction