Sinervo Barry
Department of Zoology NJ-15, University of Washington, Seattle, WA, 98195.
Evolution. 1990 Mar;44(2):279-294. doi: 10.1111/j.1558-5646.1990.tb05198.x.
I used comparative and experimental analysis of egg size in a Sceloporus lizard to examine a fundamental tenet of life-history theory: the presumed trade-offs among offspring number, offspring size, and performance traits related to offspring size that are likely to influence fitness. I analyzed latitudinal and elevational patterns of egg life-history characteristics among populations and experimentally manipulated egg size and hatchling size by removing yolk from the eggs to examine the causal bases of population differences in offspring traits. Mean clutch size among populations increased to the north (seven vs. 12 eggs/clutch, California vs. Washington), whereas egg size decreased (0.65 g vs. 0.40 g). The elevational patterns in southern California paralleled the latitudinal trends. Several offspring life-history traits that are correlated with egg size also varied geographically; these traits included incubation time, hatchling size, growth rate, and hatchling sprint performance. Hatchling viability of experimentally reduced eggs was remarkably high (~70%), even when up to 50% of the yolk was removed. The experimentally reduced eggs and hatchlings demonstrated the degree to which size influences each of the offspring life-history traits considered. Northern eggs hatched sooner, in part because of their small size. Though growth rate is allometrically related to size within each population (i.e., smaller hatchlings grow faster on a mass-specific basis), population differences in growth rate, as measured in the laboratory, are likely to reflect genetic differentiation in the underlying physiology of growth. Moreover, smaller juveniles, because of experimental reduction, had slower sprint speeds than larger juveniles. The slower sprint speed of hatchlings from Washington compared to hatchlings from California is thus largely due to the fact that eggs are smaller in the Washington population. These results provide a basis for interpreting the evolutionary divergence of the suite of traits involved in the evolution of maternal investment per offspring in lizards. For example, evolutionary divergence in some offspring traits functionally related to size (e.g., sprint speed) may be constrained, relative to traits that are determined by other aspects of development or physiology (e.g., growth). I also discuss issues relating to the evolution of maternal investment that could be tested in laboratory and natural populations using experimentally reduced offspring.
我通过对一种强棱蜥属蜥蜴的卵大小进行比较分析和实验分析，来检验生活史理论的一个基本信条：即后代数量、后代大小以及与后代大小相关的表现型性状之间可能存在的权衡取舍，而这些性状很可能会影响适合度。我分析了不同种群间卵的生活史特征的纬度和海拔模式，并通过从卵中去除卵黄来实验性地操控卵大小和幼体大小，以检验后代性状种群差异的因果基础。种群间的平均窝卵数向北增加（加利福尼亚州为每窝7枚卵，华盛顿州为每窝12枚卵），而卵大小减小（0.65克对0.40克）。南加利福尼亚州的海拔模式与纬度趋势相似。几个与卵大小相关的后代生活史性状在地理上也存在差异；这些性状包括孵化时间、幼体大小、生长速率和幼体短跑表现。实验性减小的卵的幼体存活率非常高（约70%），即使去除高达50%的卵黄也是如此。实验性减小的卵和幼体展示了大小对所考虑的每个后代生活史性状的影响程度。北方的卵孵化得更快，部分原因是其尺寸较小。尽管在每个种群中生长速率与大小呈异速生长关系（即较小的幼体在特定质量基础上生长得更快），但在实验室中测量的生长速率的种群差异很可能反映了生长基础生理学方面的遗传分化。此外，由于实验性减小，较小的幼体短跑速度比较大的幼体慢。因此，与加利福尼亚州的幼体相比，华盛顿州的幼体短跑速度较慢，这在很大程度上是因为华盛顿种群的卵较小。这些结果为解释蜥蜴中每个后代的母体投资进化过程中所涉及的一系列性状的进化分歧提供了基础。例如，相对于由发育或生理学的其他方面所决定的性状（如生长），一些与大小功能相关的后代性状（如短跑速度）的进化分歧可能受到限制。我还讨论了与母体投资进化相关的问题，这些问题可以在实验室和自然种群中通过对后代进行实验性减小来进行检验。
