Embryonic yolk removal affects a suite of larval salamander life history traits

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.