Early mortality surge in protein-deprived females causes reversal of sex differential of life expectancy in Mediterranean fruit flies

Abstract

Experiments based on over 400,000 medf lies revealed that females maintained on a normal diet (sucrose plus protein) have a higher life expectancy than males maintained on a normal diet, with a difference of 1.30 ؎ 0.27 days in favor of females. However, this sex differential reverses under protein deprivation, with a difference of 2.24 ؎ 0.18 days in favor of males. The reversal of the male-female life expectancy differential is caused by a sustained surge in early female mortality under protein deprivation that is tied to egg-laying and physiological processes. In contrast, male mortality and life expectancy are only mildly affected by protein deprivation. The surge in early mortality for female medf ly cohorts is an instance of a vulnerable period. These vulnerable periods are linked with patterns in hazard rates.Life expectancy or average lifespan of individuals is an important quantitative characteristic for comparing the survival and thus frailty of cohorts subjected to various genetic and͞or environmental influences. Genetic factors play an important role in determining life expectancy, as exemplified by the well-known sex differential in life expectancy (1-4). Although life expectancy is an overall measure of longevity, the specific dynamics of mortality and the aging process are reflected by the hazard rate or force of mortality.We report the results of an experiment concerning the survival of cohorts of male and female Mediterranean fruit flies (Ceratitis capitata) under a full sugar-plus-protein diet and under protein deprivation (sugar only). The motive for this study was our interest in determining why hazard rates in female medflies began to level off at an earlier age and at a lower level than hazard rates in male medflies. These mortality patterns were observed in several recent studies involving a total of more than 1.2 million medflies (5), all of which were protein-deprived. We initiated the current investigation to see whether this phenomenon was due to protein deprivation and whether protein deprivation has a sex-dependent effect on life expectancy and hazard rates. MATERIALS AND METHODSWe investigated these issues by maintaining large cohorts of medflies at the Moscamed medfly mass-rearing facility located in Metapa, Chiapas, Mexico. Technical details on fruit fly mass rearing are as described in ref. 6. Adult flies were maintained under the following environmental conditions: 12-h͞12-h light͞dark cycle, 24.0ЊC (Ϯ2ЊC), and 65% relative humidity (Ϯ9%). Medflies were kept on one of two dietary regimes: (i) a sugar-plus-protein diet in which flies were provided with sucrose and a protein source; and (ii) a proteinfree diet in which flies were provided with a diet consisting only of sucrose (protein-deprived). A total of 416,289 medflies (about equally divided between males and females) were maintained in 66 aluminum cages, 15 ϫ 60 ϫ 90 cm, each containing about 6,000 medflies, males and females grouped together. Thirty-three cages were assigned to the sugar-plusprotein diet and the oth...

Effects of different protein concentrations on longevity and feeding behavior of two adult populations of Ceratitis capitata Wiedemann (Diptera: Tephritidae)

“…In general, females lived longer than males although no relationship was established between sex and diet quality. However, Muller et al (1997) found that females lived longer than males when both were fed on protein diets. Considering the important role of protein for egg production, we expected that females fed on the no-protein diet would live less than males reared under the same conditions, given that previous studies have shown a higher reproductive cost for females than for males, and lower female longevity (Chapman et al 1995(Chapman et al , 1998.…”

Evolutionary Optimality Applied to Drosophila Experiments: Hypothesis of Constrained Reproductive Efficiency

“…The reproductive contours technique, in principle, allows for the quantification of trade-offs induced by temperature manipulations, mating-and fecundity-related manipulations (Partridge et al 1987;Partridge 1989;Sgro and Partridge 1999), and diet-related manipulations (Chippindale et al 1993;Mü ller et al 1997;Simmons and Bradley 1997) in Drosophila. It is possible to proceed with the work to study the diversity of life-history patterns in other species such as Mediterranean fruit flies (Carey et al 1998) and Callosobruchus maculatus (Tatar et al 1993;Tatar and Carey 1995).…”

A mortality cost of virginity at older ages in female Mediterranean fruit flies

“…Because of the central importance of the reproductive and mating cost concept to theories of aging (Kirkwood and Rose, 1991;Rose and Charlesworth, 1980) and for understanding male-female mortality differentials (Hazzard, 1986(Hazzard, , 1990, we conducted experiments to determine whether the effects of mating in females were beneficial at older ages relative to virginity, as reflected in mortality rates of virgin and non-virgin cohorts. The current paper builds on the general findings from previous research on the mortality dynamics of the Mediterranean fruit fly, Ceratitis capitata (Carey, 1999;Carey and Liedo, 1999a,b;Carey et al, , 1999Müller et al, 1997aMüller et al, ,b, 2001Vaupel et al, 1998) including a recent modeling paper in which the data presented in this paper were used to test the hypothesis that oxidative damage accounted for differences in the mortality trajectory of virgin versus mated medflies (Novoseltsev et al, 2000).…”