A quantitative genetic analysis of nine adult fitness components was performed in two populations of cactophilic Drosophila mojavensis under natural conditions of fermenting cactus and ethanol vapour. Female progeny from 18 sires and 36 dams were treated to a range of six exposure periods to males to assess effects of remating frequency on female fitness. Lifetime fecundity increased with increasing male exposure, but longevity showed an intermediate optimum with temporary exposure to males of 2-4 days. Narrow-sense heritabilities were significant for egg production traits while broad-sense heritabilities were significant for longevity-related traits. Positive genetic correlations between components of fitness were expressed among functionally related traits, e.g. longevity was positively correlated with lifetime fecundity, the number of clutches laid, clutch size, and the number of eggs laid per day. Negative genetic correlations were detected between early and late life fecundity suggesting genetic tradeoffs among components of adult fitness.Keywords: cactus, Drosophila, genetic correlation, heritability, life history, remating.
IntroductionThe degree of parental investment in their genetic progeny is thought to result from a balance between future reproductive success and the immediate costs of parental care through investment of resources in current offspring. This classical tradeoff envisioned by Trivers (1972) has been perceived as a driving force in the evolution of plant and animal mating systems, particularly where sexual selection is involved (Parker, 1979). In many insect species, paternal contributions are essential elements of courtship behaviour and serve as nuptial gifts prior to copulation (Zeh & Smith, 1985). These paternal contributions include the provision of food captured or glandular secretions provided by males (Thornhill & Alcock, 1983). These contributions are presumably adaptive because they increase male mating success and may influence the fitness of his progeny. If females can choose males on the basis of their ability to provide, and such behaviour increases female fitness, sexual selection should reinforce natural selection and males that provide larger contributions will be favoured.The paternal contribution of substances other than *Correspondence 515 sperm used by females after copulation is well documented in 10 orders of insects (Thornhill & Alcock, 1983;Boggs, 1990). Within the Drosophilidae, paternal investment may involve courtship feeding (Steele, 1986a, b), where males present a nuptial gift of regurgitated food to the female as part of courtship behaviour or the direct contribution of ejaculate compounds that females assimilate into somatic and reproductive tissues (Chen & Buhier, 1970;Baumann, 1974;Markow & Ankney, 1984; Scott, 1986;Bownes & Partridge, 1987;Markow et al., 1990). Many compounds are present in the ejaculate of Drosophila males that can influence female receptivity to remating (Mane et a!., 1983; Scott, 1986), increase oviposition rates (Chen, 1984), and ...