Landberg Tobias
University of Connecticut, Ecology & Evolutionary Biology, Storrs, Connecticut.
J Exp Zool B Mol Dev Evol. 2014 Jan;322(1):45-53. doi: 10.1002/jez.b.22544. Epub 2013 Oct 28.
Egg size is a key life history trait affecting fitness, and it varies abundantly. The value of egg size to a mother and her offspring is often determined by a trade-off between investing more yolk in a few large eggs or less yolk into many more, smaller eggs. Smaller eggs are generally expected to be phenotypically inferior or females could increase their fitness by making more smaller eggs. However, many females produce a mix of egg sizes and natural yolk variation induces normal developmental responses which may persist into subsequent stages of a complex life history. Since sources of phenotypic variation are easily confounded, I surgically removed yolk from embryonic spotted salamanders (Ambystoma maculatum) using a sham surgery as a control and a split-clutch design to isolate the effects of yolk reserve variation from genetic sources of variation. Yolk removal induced early hatching, reduced developmental stage and hatchling body size. Small hatchlings stayed relatively small through the early larval period, but 17 weeks later the correlation with early larval body size was lost. When the experiment ended, larger individuals were further along in metamorphic development but mortality was independent of early larval body size. Variation in spotted salamander yolk reserves affects a suite of hatchling life history traits that persists into the larval period. Outside the laboratory, egg size effects may cascade throughout complex amphibian life histories. Applied experimentally and comparatively, this simple yolk removal technique may help identify how traits increase or decrease their response to maternal yolk investment.
卵的大小是影响适合度的关键生活史特征，并且其变化很大。卵的大小对母体及其后代的价值通常由在少数几个大卵中投入更多卵黄与在更多较小的卵中投入较少卵黄之间的权衡来决定。一般认为较小的卵在表型上较差，否则雌性可以通过产出更多较小的卵来提高其适合度。然而，许多雌性会产出大小不一的卵，并且天然卵黄的变化会引发正常的发育反应，这些反应可能会持续到复杂生活史的后续阶段。由于表型变异的来源很容易混淆，我通过手术从胚胎期的黄斑蝾螈（Ambystoma maculatum）中取出卵黄，使用假手术作为对照，并采用分窝设计来分离卵黄储备变异与遗传变异来源的影响。去除卵黄会导致提前孵化、发育阶段降低和幼体体型减小。小幼体在幼体早期阶段相对体型较小，但17周后与幼体早期体型的相关性消失。当实验结束时，较大的个体在变态发育中进展更远，但死亡率与幼体早期体型无关。黄斑蝾螈卵黄储备的变异会影响一系列持续到幼体期的幼体生活史特征。在实验室之外，卵大小的影响可能会贯穿复杂的两栖动物生活史。通过实验应用和比较，这种简单的去除卵黄技术可能有助于确定性状如何增加或减少它们对母体卵黄投入的反应。
