A Cost of Reproduction in Drosophila Melanogaster: Stress Susceptibility

Abstract

Abstract. 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. The cost of reproduction is a relationship of central importance in life-history theory (Williams 1966). Demographically, the cost of present reproduction is paid in terms of reduced future reproduction and decreased longevity (Bell and Koufopanou 1986;Stearns 1991). The cost of reproduction has been documented in numerous studies on plants and animals (reviewed in Roff 1992) in terms of phenotypic correlations, experimental manipulations, genetic correlations, and correlated responses to selection (reviewed in Reznick 1985). However, relatively little is known about the mechanistic underpinnings of this fundamental relationship. Stearns (1991) argued it is important to investigate life-history trade-offs from the viewpoint of mechanisms. It is essential to delineate mechanisms underlying trade-offs to understand how life histories evolve. Life-history trade-offs are thought to evolve around constraints such as limiting commodities (energy, space) or structural components, which can optimize one function but not another simultaneously. Partridge (1989) identified Drosophila melanogaster costs of reproduction associated with egg production and with mating. The cost of egg production (Partridge et al. 1987;Partridge 1989) results in a time lag impact on age-specific mortality (Sgro and Partridge 1999). In addition, exposure of females to males without mating reduces the life span of females (Partridge and Fowler 1990). Mating has a major deleterious effect on female longevity resulting from the transfer of male accessory gland secretion at the time of mating but not from the transfer of sperm (Chapman et al. 1993(Chapman et al. , 1995. If the female response to the male accessory gland sex peptide is blocked, then the mating cost of reproduction increases (Chapman et al. 1996).Lines of D. melanogaster selected for increased longevity and late-age reproduction have been used to investigate the cost of reproduction. One such set of lines (Rose 1984) 2 Present addr...

Reproductive protein protects functionally sterile honey bee workers from oxidative stress

“…53). JH increases female reproduction, reduces tolerance to oxidative stress, and shortens lifespan in the fly (4,30). Also, ablation of Drosophila insulin peptide synthesizing cells reduces fertility, elevates oxidative stress resistance, and extends longevity (54).…”

“…We suggest that a changed connection between vitellogenin activity and aging in the bee can be understood by the role of decoupling of caste physiologies in social insect evolution (12,13) and selection on longevity in species with continuing care for offspring (46)(47)(48). Specifically, life-history evolution in the bee, which provides continuing care via alloparents stemming from a single reproductive female, favored a positive link between vitellogenin activity and lifespan over the negative association (3,30) we assume is the ancestral condition.…”

“…JH is part of the IIS pathway in Drosophila (5) that coregulates yolk peptide expression and somatic maintenance antagonistically (1,4,(28)(29)(30). In C. elegans, reduced activity of the vitellogenin-encoding genes vit-2 and vit-5 (which are downstream of the IIS receptor Daf-2) lengthens lifespan (3).…”

“…Oxidative modification of intracellular proteins is a major aspect of senescence (40, 41), and loss of oxidative stress resistance is a biomarker of aging in the nematode, fly, and mouse (5). Thus, the role of vitellogenin in honey bee aging could deviate substantially from the effect of yolk precursor gene activity (3) in the aging machineries (4,5,28,30) of the distantly related solitary invertebrates that have been studied. However, a positive connection between vitellogenin activity and longevity first has to be established.…”

“…Here, we investigated whether a pathway of aging in a eusocial organism diverges from the current model in the published literature (3,30) by testing the hypothesis that vitellogenin protects the bee from oxidative stress. Workers were studied because a vitellogenin RNA interference (RNAi) method is established for this caste (42).…”