Skeletal patterns in the autopodium of native and regenerated limbs of the larval axolotl, Ambystoma mexicanum

Abstract

The purpose of this investigation was to study the autopodial skeletal patterns that are observed in native (never regenerated) and regenerated limbs of the larval axolotl, Ambystoma mexicanum. The axolotl is used widely in limb regeneration studies, and in the regenerating axolotl limb mesopodial patterns can be modified by such factors as vitamin A administration. It is also known that other salamander species show significant variation in autopodial skeletal patterning. Hence, it seemed important to determine the type and frequency of autopodial variants in both native limbs and those that have regenerated after amputation at either the stylopodial and zeugopodial levels. The results showed that native limbs exhibited a complete skeletal pattern in the majority of cases, but that variants involving loss of a phalange or reduction in the number of carpals or tarsals occurred frequently. Regenerated limb patterns were more variable than those seen in native limbs, and limbs regenerating from zeugopodial level amputations were more variable than those regenerating from stylopodial level amputation. The significance of these observations for the development and regeneration of limb pattern is discussed.