Khazaeli A A, Pletcher S D, Curtsinger J W
Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul 55108, USA.
Mech Ageing Dev. 1998 Nov 16;105(3):301-17. 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 51331 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.
在基因同质和异质的果蝇种群中，特定年龄死亡率在老年时都会减缓。针对这种减缓现象提出的一种解释是种群异质性。该假说认为，一个种群由死亡率特征不同的亚种群组成，而死亡率减缓是更强壮个体选择性存活的结果。在此，我们描述了一项实验，该实验将种群分成几个亚种群，同时不改变分群后种群的生理特征。通过精心挑选果蝇的卵、幼虫、蛹和成虫，我们试图尽可能降低基因相同群体中个体间成年前由环境诱导产生的异质性程度。然后，我们探究与未分群的种群相比，这样的群体在老年时是否表现出较低程度的死亡率减缓。在总共106个分群和对照种群（由51331个个体组成）中，101个种群（93%的分群种群和100%的对照种群）在生命后期表现出显著的死亡率减缓。这些观察结果表明，幼虫发育期间积累的环境异质性并非导致老年死亡率减缓的主要因素。
