The great British ornithologist David Lack proposed a hypothesis to explain the evolution of the number and the size of eggs laid in a clutch by a female bird. He proposed that evolution will favor females that lay intermediate sized eggs and clutches. Females that lay many small eggs will start with more offspring, but these offspring will be small and may have a low chance of survival. Females that lay few large eggs increase survival chances of their offspring, but start with fewer of them. Thus females that lay an intermediate number and size of eggs are likely to have the most surviving offspring. The investigators have developed the first experimental test of Lack's Hypothesis as it applies to egg size in lizards. They will release hatchlings from clutches with large versus small eggs, and then monitor their survivorship and age to first reproduction. Using novel techniques, they can produce "giant" and "miniaturized" hatchlings that enable them to control hatchling size independent of genotype. Thus, they will determine actual patterns of selection on egg size. These studies not only test a fundamental issue in evolutionary ecology, but also have important practical implications as well. Captive breeding programs (salmon, trout, sea turtles) have ignored the importance of egg size on future survivorship. These experiments will show whether that is wise and whether those breeding protocols require revision.
