Heterochrony and Frogs: The Relationship of a Life History Trait to Morphological Form

Frog species are often characterized by minor differences in relative hind-limb length. Although the length of the hind limb generally correlates with locomotor performance, differences between closely related species are often too small to affect jumping ability significantly. Thus, it seems unlikely that the selection for relative hind-limb length is the source of the differences. Rather, heterochrony is suggested as a source of these minor shape variants, since it is known that (1) hind-limb and body lengths scale allometrically in frogs during development, and (2) there are significant differences in relative hind-limb length in frogs when the developmental time is altered. Some possible evolutionary and ecological ramifications of such an association between a life history trait and a species-typical morphological feature are discussed.