Bryant Michael J, Reznick David
Department of Biology, University of California, Riverside, California, 92521,USA.
Am Nat. 2004 Jan;163(1):55-68. doi: 10.1086/380650. Epub 2004 Jan 28.
Investigators have rarely sought evidence for senescence in natural populations because it is assumed that relatively few individuals will survive long enough in the wild to exhibit the intrinsic increase in mortality with age expected from senescent individuals. Nevertheless, senescence has been documented in some natural populations, mostly in birds and mammals. Here we report on a comparative study of senescence in two natural populations of guppies (Poecilia reticulata). We document senescence as an age-specific increase in mortality rate, with use of mark-recapture studies and implementation of program MARK for analysis of such observations. Extrinsic mortality was controlled for by choosing populations that experience low rates of predation because they coexist with only a single piscine predator (Rivulus hartii). These populations differ in their evolutionary history because one was native to such a site whereas the other was introduced to a site that previously contained no guppies. The source of the introduced guppies was a high-predation population downstream below a barrier waterfall. Theory predicts that the guppies derived from a high-predation locality should experience senescence at an earlier age than the native low-predation population; however, the historical differences among these populations are also confounded with everything else that differs among the two localities. We found that females from a natural low-predation population have delayed senescence compared with the recently established population and hence that the differences among localities in senescence conform to theoretical predictions. The males from natural low-predation environments also had lower overall mortality rates, but contrary to predictions, the pattern of senescence for males did not differ between populations. The difference between the sexes is potentially attributable to two factors that lower the statistical power for distinguishing differences in the age-specific acceleration of mortality in males. One factor is that males have higher mortality rates, so fewer survive to advanced ages. A second is that we had a greater ability to discriminate among older age classes in females. We also found that the introduced population sustained a higher rate of disease than the native low-predation population. Such disease may represent a confounding factor in our comparison, but it may also reflect one of the trade-offs inherent in the life-history differences of these populations.
研究人员很少在自然种群中寻找衰老的证据，因为人们认为，在野外相对较少的个体能够存活足够长的时间，以展现出衰老个体预期的随着年龄增长而出现的死亡率内在增加。然而，衰老现象已在一些自然种群中得到记录，主要是在鸟类和哺乳动物中。在此，我们报告一项对孔雀鱼（孔雀鱼属）两个自然种群衰老情况的比较研究。我们通过标记重捕研究以及使用MARK程序对这些观察结果进行分析，将衰老记录为死亡率随年龄增长而增加的现象。通过选择与单一鱼类捕食者（哈氏溪鳉）共存、捕食率较低的种群来控制外在死亡率。这些种群在进化历史上有所不同，因为一个种群原产于这样的地点，而另一个种群是被引入到一个先前没有孔雀鱼的地点。引入的孔雀鱼来源是屏障瀑布下游的一个高捕食压力种群。理论预测，来自高捕食压力地区的孔雀鱼应该比本地低捕食压力种群更早出现衰老；然而，这些种群之间的历史差异也与两个地点之间其他所有不同之处相互混淆。我们发现，与新建立的种群相比，自然低捕食压力种群的雌性衰老出现延迟，因此，不同地点之间衰老情况的差异符合理论预测。来自自然低捕食压力环境的雄性总体死亡率也较低，但与预测相反，不同种群雄性的衰老模式没有差异。两性之间的差异可能归因于两个因素，这两个因素降低了区分雄性死亡率随年龄增长加速差异的统计效力。一个因素是雄性死亡率较高，所以活到高龄的个体较少。另一个因素是我们在区分雌性较老年龄组方面能力更强。我们还发现，引入的种群疾病发生率高于本地低捕食压力种群。这种疾病可能是我们比较中的一个混杂因素，但它也可能反映了这些种群生活史差异中固有的权衡之一。
