A cost of reproduction in Drosophila melanogaster: stress susceptibility.

Little is known about physiological mechanisms that underlie the cost of reproduction. We tested the hypothesis that stress susceptibility is a cost of reproduction. In one test of our hypothesis, Drosophila melanogaster females were exposed to a juvenile hormone analog (methoprene) to stimulate egg production followed by stress assays. A sterile stock of D. melanogaster was employed as a control for reproduction. Exposure of fertile females to methoprene resulted in an increase in female reproduction and increased susceptibility to oxidative stress and starvation (compared to solvent controls). Sterile females did not exhibit a decrease in stress resistance. Mating also stimulated egg production. As a second test of our hypothesis, mated females were compared to virgin females. Mated fertile females were relatively susceptible to oxidative stress, but this relationship was not evident when mated and virgin sterile females were compared. The results of the present study support the hypothesis that stress susceptibility is a cost of reproduction.

A cost of reproduction: oxidative stress susceptibility is associated with increased egg production in Drosophila melanogaster.

The present study tests the hypothesis that reproduction is correlated with decreased oxidative stress resistance. In numerous species, it has been observed that longevity is negatively correlated with reproduction but the physiological basis of this cost is not well understood. In the present study, female egg production was stimulated by adding live yeast to the surface of Drosophila food. After females were held on yeast-supplemented and unmodified medium for 6-12 days, susceptibility to oxidative stress was measured by exposure to methyl viologen. Added yeast was associated with stress susceptibility of fertile females but not of sterile females. The results of the present study suggest that oxidative stress susceptibility is a physiological cost of reproduction.

Breeding experience and parental behaviour in convict cichlids (Cichlasoma nigrofasciatum ).

Changes in the levels of activities by parental female and male convict cichlids were studied over three successive reproductive episodes and within each episode. No evidence was found for behavioural maturation independent of experience. With successive episodes, young survived for longer times, nests were cleaner, males ate less and females more, and males became more aggressive while females focused more on the nest. Within an episode there were also marked variations in activities by each sex. Reproductive behaviour is therefore open in a number of respects both within and across episodes to environmental inputs.