Sinervo Barry, DeNardo Dale F
Department of Biology, Jordan Hall, Indiana University, Bloomington, Indiana, 47405.
Department of Integrative Biology, University of California, Berkeley, California, 94720.
Evolution. 1996 Jun;50(3):1299-1313. doi: 10.1111/j.1558-5646.1996.tb02370.x.
During 1991 through 1994, natural selection on reproductive effort in side-blotched lizards was indexed by measuring total clutch mass produced on the first clutch of the reproductive season and assessing how such effort in current reproduction affects subsequent survival and clutch production. In addition, selection was also experimentally assessed in free-ranging female side-blotched lizards by (1) surgically decreasing total clutch mass (direct ovarian manipulation) and enhancing clutch mass using (2) exogenous gonadotropin, and (3) exogenous corticosterone. Surgical reduction of clutch mass uniformly enhanced survival. However, increasing clutch mass had more complex effects depending on year. Experimentally enhanced clutch mass enhanced survival in 1991, had no effect on survival in 1992, and decreased survival in 1993. Despite the complexity of these experimental results, they are corroborated by our comparative data. It is important to note that local environmental effects can obscure detection of costs arising from natural variation in reproductive effort, and we removed such effects using path analysis. The striking shift in natural selection favoring females laying a large clutch mass (1991) to selection against females laying a large clutch mass (1993) is associated with an end of a severe multiyear drought. Our natural-history observations suggest that the correlated increase in predatory snake activity on our study site, coincident with the end of the drought, is the agent of natural selection. Although the actual agents of selection (e.g., snake predation versus drought-related effects) are not resolved, the patterns of natural selection measured in our comparative and experimental data are also consistent with year-to-year changes in clutch mass and egg size that would be indicative of rapid short-term evolution in these traits.
在1991年至1994年期间，通过测量繁殖季节首次产卵的总窝卵质量，并评估当前繁殖中的这种投入如何影响后续的生存和窝卵生产，来衡量侧斑蜥蜴繁殖投入的自然选择。此外，还通过以下方式对自由放养的雌性侧斑蜥蜴进行了实验性评估：（1）通过手术减少总窝卵质量（直接卵巢操作），以及使用（2）外源性促性腺激素和（3）外源性皮质酮来增加窝卵质量。手术减少窝卵质量一致地提高了生存率。然而，增加窝卵质量的影响因年份而异，更为复杂。实验性增加窝卵质量在1991年提高了生存率，在1992年对生存率没有影响，而在1993年降低了生存率。尽管这些实验结果很复杂，但我们的比较数据证实了它们。需要注意的是，局部环境影响可能会掩盖因繁殖投入的自然变异而产生的成本的检测，我们使用路径分析消除了这种影响。自然选择从有利于产大窝卵的雌性（1991年）显著转变为不利于产大窝卵的雌性（1993年），这与一场严重的多年干旱的结束有关。我们的自然史观察表明，在我们的研究地点，与干旱结束同时发生的捕食性蛇类活动的相应增加是自然选择的动因。尽管实际的选择动因（例如，蛇的捕食与干旱相关的影响）尚未确定，但我们在比较和实验数据中测量到的自然选择模式也与窝卵质量和卵大小的逐年变化一致，这表明这些性状在短期内迅速进化。
