The effects of selection for early and late reproduction on metabolite pools in Acanthoscelides obtectus Say

The present study was aimed at revealing the responses of metabolite pools to selection for alternative reproductive schedules in the seed beetle, Acanthoscelides obtectus Say （Coleoptera： Chrysomelidae： Bruchinae）. The levels of metabolites （free sugars, glycogen, lipids, soluble and hydrophobic proteins） that were determined in virgin females and males at three ages from adult eclosion onwards were compared among the base population （B） and two derived lines that were selected for either early （Y） or late （O） reproduction. The results showed differences in the accumulation of metabolites during pre-adult development, as well as in the pattern of their changes during adult ageing, Generally, in comparison to the B population, the short-lived beetles from the Y line showed increased protein content and reduced carbohydrate and lipid content, whereas the opposite was true for the long-lived beetles from the O line. Females from the O line exhibited slower utilization of energy reserves and a slower increase in protein contents than females from the Y line. Females contained higher levels of free sugars, glycogen and hydrophobic proteins and lower levels of lipids and soluble proteins than males, although the sexual dimorphism was not evenly expressed among lines. Age-specific changes in metabolite contents were slower in females than males. Our findings suggest that trade-offs among capital resources are a physiological basis of early/late fitness trade-offs and point to a conservation of resources that can be used for somatic maintenance.

Heterosis in age-specific selected populations of a seed beetle： Sex differences in longevity and reproductive behavior

We tested mutation accumulation hypothesis for the evolution of senescence using short-lived and long-lived populations of the seed-feeding beetle, Acanthoscelides obtectus （Say）, obtained by selection on early- and late-life for many generations. The expected consequence of the mutation accumulation hypothesis is that in short-lived pop- ulations, where the force of natural selection is the strongest early in life, the late-life fitness traits should decline due to genetic drift which increases the frequency of mutations with deleterious effects in later adult stages. Since it is unlikely that identical deleterious mutations will increase in several independent populations, hybrid vigor for late-life fit- ness is expected in offspring obtained in crosses among populations selected for early-life fitness traits. We tested longevity of both sexes, female fecundity and male reproductive behavior for hybrid vigor by comparing hybrid and nonhybrid short-lived populations. Hybrid vigor was confirmed for male virility, mating speed and copulation duration, and longevity of both sexes at late ages. In contrast to males, the results on female fecundity in short-lived populations did not support mutation accumulation as a genetic mechanism for the evolution of this trait. Contrary to the prediction of this hypothesis, male mating ability indices and female fecundity in long-lived populations exhibited hybrid vigor at all assayed age classes. We demonstrate that nonhybrid long-lived populations diverged randomly regarding female and male reproductive fitness, indicating that sexually antag- onistic selection, when accompanied with genetic drift for female fecundity and male virility, might be responsible for overriding natural selection in the independently evolving long-lived populations.