Reznick David N, Bryga Heather
Department of Biology, University of California, Riverside, CA, 92521.
Evolution. 1987 Nov;41(6):1370-1385. doi: 10.1111/j.1558-5646.1987.tb02474.x.
Previous investigations (Reznick and Endler, 1982; Reznick, 1982a, 1982b) demonstrated that genetic differences in guppy life histories were associated with differences in predation. Guppies from localities with the pike cichlid Crenicichla alta and associated predators matured earlier, had greater reproductive efforts, and produced more and smaller offspring than did guppies from localities with only Rivulus harti as a potential predator. Crenicichla preys primarily on large, sexually mature size-classes of guppies, while Rivulus preys primarily on small, immature size-classes. These patterns of predation are hypothesized to alter mean age-specific survival. Theoretical treatments of such differences in survival predict the observed trends in age at maturity and reproductive effort. We are using introduction experiments to evaluate the role of predators in selecting for these life-history patterns. The experiment whose results are presented here was conducted in a tributary to the El Cedro River (Trinidad), where a waterfall was the upstream limit to the distribution of all fish except Rivulus. Guppies collected from the Crenicichla locality immediately below the waterfall (the downstream control) were introduced over the waterfall in 1981. This introduction released the guppies from Crenicichla predation, exposed them instead to Rivulus predation only, and also introduced them to a different environment, since the introduction site has greater canopy cover than the site of origin. Changes in guppy life-history patterns can be attributed to predation and/or the environment. Evidence from fish collected and preserved in the field demonstrated that, by mid-1983, guppies from the introduction site above the waterfall matured at larger sizes and produced fewer, larger offspring. There were no consistent differences in reproductive allotment (weight of offspring/total weight). With the exception of reproductive allotment, these patterns are identical to previous comparisons between Rivulus and Crenicichla localities. A laboratory genetics experiment demonstrated that males from the introduction site matured at a later age and at a larger size than did males from the control site downstream, as predicted from the "age-specific predation" hypothesis. No differences between localities were observed for female age and size at maturity or for reproductive effort. The trends for fecundity and offspring size were the reverse of those observed in the field. Because only the males changed in the predicted fashion, it is not possible either to reject or to accept the hypothesis of age-specific predation at this time. We discuss the possible causes for these patterns and the high degree of plasticity in the life history, as evidenced by the differences in fecundity and offspring size between the field and laboratory results.
先前的研究（雷兹尼克和恩德勒，1982年；雷兹尼克，1982a，1982b）表明，孔雀鱼生活史中的遗传差异与捕食差异有关。与只有哈氏溪鳉作为潜在捕食者的地区的孔雀鱼相比，来自有高身丽鱼及相关捕食者地区的孔雀鱼成熟更早，繁殖投入更大，产出的后代数量更多但个体更小。高身丽鱼主要捕食体型较大、性成熟的孔雀鱼，而溪鳉主要捕食体型较小、未成熟阶段的孔雀鱼。据推测，这些捕食模式会改变特定年龄的平均存活率。对这种存活率差异的理论分析预测了成熟年龄和繁殖投入方面观察到的趋势。我们正在通过引入实验来评估捕食者在选择这些生活史模式中所起的作用。此处展示结果的实验是在埃尔塞德罗河（特立尼达）的一条支流中进行的，那里有一道瀑布是除溪鳉外所有鱼类分布的上游界限。1981年，从瀑布正下方高身丽鱼所在地区采集的孔雀鱼（下游对照）被引入瀑布上方。这次引入使孔雀鱼摆脱了高身丽鱼的捕食，转而仅面临溪鳉的捕食，同时也将它们引入了一个不同的环境，因为引入地点的树冠覆盖比原产地更大。孔雀鱼生活史模式的变化可归因于捕食和/或环境。对在野外采集并保存的鱼类的证据表明，到1983年年中，瀑布上方引入地点的孔雀鱼成熟时体型更大，产出的后代数量更少但个体更大。繁殖分配（后代重量/总重量）没有一致的差异。除了繁殖分配外，这些模式与先前对溪鳉和高身丽鱼所在地区的比较相同。一项实验室遗传学实验表明，正如“特定年龄捕食”假说所预测的那样，来自引入地点的雄性孔雀鱼比下游对照地点的雄性孔雀鱼成熟年龄更晚、体型更大。在成熟时的雌性年龄和体型或繁殖投入方面，未观察到不同地点之间存在差异。繁殖力和后代大小的趋势与在野外观察到的相反。由于只有雄性以预测的方式发生了变化，所以此时既无法拒绝也无法接受特定年龄捕食的假说。我们讨论了这些模式的可能原因以及生活史中的高度可塑性，野外和实验室结果在繁殖力和后代大小方面的差异证明了这一点。
