The fractionation experiment: reducing heterogeneity to investigate age-specific mortality in Drosophila

• Published in: Mechanisms of ageing and development Vol. 105; no. 3; pp. 301 - 317
• Main Authors: Khazaeli, Aziz A., Pletcher, Scott D., Curtsinger, James W.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 16.11.1998; Elsevier Science
• Subjects: Aging - genetics; Aging - physiology; Animals; Biological and medical sciences; Computer Simulation; Development. Metamorphosis. Moult. Ageing; Drosophila; Drosophila melanogaster - genetics; Drosophila melanogaster - physiology; Female; Fractionation; Fundamental and applied biological sciences. Psychology; Genetic Heterogeneity; Heterogeneity; Leveling off; Male; Models, Genetic; Mortality; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Heterogeneity; Fractionation; Leveling off; Mortality; Drosophila; Senescence; Insecta; Environmental factor; Drosophilidae; Larva; Arthropoda; Animal; Development; Invertebrata; Animal population; Diptera; Age
• ISSN: 0047-6374; 1872-6216
• DOI: 10.1016/S0047-6374(98)00102-X

Age-specific mortality rates decelerate at older ages in both genetically homogenous and heterogeneous populations of Drosophila. One explanation proposed for deceleration is population heterogeneity. This hypothesis suggests that a population consists of sub-populations that differ in mortality characteristics and that the deceleration is the result of selective survival of stronger individuals. Here we describe an experiment that fractionates populations into several sub-populations without changing the physiological characteristics of the post-fractionated populations. Through a careful process of selection of Drosophila eggs, larvae, pupae and adults, we attempt to reduce as much as possible the degree of pre-adult, environmentally induced heterogeneity among individuals of a genetically identical cohort. We then ask whether such cohorts, when compared to non-fractionated populations, exhibit a lesser degree of mortality deceleration at advanced ages. From a total of 106 fractionated and control populations, consisting of 51 331 individuals, 101 populations (93% of the fractionated populations and 100% of the control populations) exhibit a significant amount of mortality deceleration late in life. These observations suggest that environmental heterogeneity accrued during larval development is not a major factor contributing to mortality deceleration at older ages.