Allometric engineering: an experimental test of the causes of interpopulational differences in performance

Hatchling lizards (Sceloporus occidentalis) from a southern population are large and have high locomotor performance (speed and stamina) relative to hatchlings from northern populations. In order to determine whether differences in performance are an allometric consequence of interpopulation differences in size, yolk was removed from southern eggs, thereby producing miniaturized hatchlings equivalent in size to northern hatchlings. Miniaturized southern hatchlings no longer had higher speed than northern hatchlings, but maintained higher stamina. Interpopulation differences in speed but not in stamina are thus an allometric consequence of differences in egg size. Size manipulation adds an experimental dimension to aliometric analyses.