Longevity in the protozoa

What's Genetic Variation Got to Do with It? Starvation-Induced Self-Fertilization Enhances Survival in Paramecium

The pervasiveness of sex despite its well-known costs is a long-standing puzzle in evolutionary biology. Current explanations for the success of sex in nature largely rely on the adaptive significance of the new or rare genotypes that sex may generate. Less explored is the possibility that sex-underlying molecular mechanisms can enhance fitness and convey benefits to the individuals that bear the immediate costs of sex. Here, we show that the molecular environment associated with self-fertilization can increase stress resistance in the ciliate Paramecium tetraurelia. This advantage is independent of new genetic variation, coupled with a reduced nutritional input, and offers fresh insights into the mechanistic origin of sex. In addition to providing evidence that the molecular underpinnings of sexual reproduction and the stress response are linked in P. tetraurelia, these findings supply an integrative explanation for the persistence of self-fertilization in this ciliate.

An alpha-tocopherol dose response study in Paramecium tetraurelia

Vitamin E (D,L-alpha-tocopherol) was administered to Paramecium tetraurelia in doses of 10, 100, 1000 and 10,000mg/l throughout its clonal lifespan. ANOVA revealed significant differences in clonal lifespan between groups, whether lifespan was measured in total fissions, or in days (P<0.05). When mean clonal lifespan was measured in fissions the greatest difference was between the 1000mg/l alpha-tocopherol treatment at 382 fissions, and the ethanol control at 255.5 fissions. The greatest difference in mean clonal lifespan in days survived was between the 10,000mg/l alpha-tocopherol treatment at 292.5 days and the ethanol control at 76 days. ANOVA also revealed significant differences (P<0.05) in the initial cell fission rates between groups. At the 1000 and 10,000mg/l concentrations of alpha-tocopherol, a decrease in cell fission rates was apparent early in the lifespan, but these rates began to increase gradually during the late clonal lifespan. Although no clonal toxicity effects were found in terms of decreasing life-expectancy, the 1000 and 10,000mg/l treatment groups exhibited higher background mortality rates throughout their respective lifespans than did the control groups, which could represent a cytotoxic effect.

Body composition and longevity: is there a longevous morphotype?

Life expectancies are increasing in populations throughout the world. As infectious diseases decline as causes of mortality, certain degenerative diseases including cardiovascular disease and cancer account for an increasing percentage of deaths. As more people survive into old age, the intrinsic limits on the human life span will be reached. It is clear that genetic factors have a strong influence on the life span. It is not clear, however, that there are identifiable longevous body types (morphotypes). For the first time in human history, large numbers of people 80 years old and older are available for study. If there is an association between body form and composition and superior longevity, it should be possible to identify its major aspects. Monitoring changes in body composition throughout the life cycle and the retention of reserves to be drawn upon when disease or trauma threaten life may provide the basis for prediction of the course of life threatening diseases. The unusually high survival of morphotypes classifiable as "moderately obese" casts doubt on standards recommending "ideal weights for height" if the criterion in question is survival.