Rudimentary, "functionless" first metapodials of Canis latrans: Variation and association in length with longer, functional metapodials.

A tenet of evolutionary theory is that phenotypic variation of a trait is inversely related to the intensity of stabilizing selection pressure. Among homologous bones, such as metapodials, a rudimentary, "nonfunctional" bone is expected to be more variable in length than nonrudimentary bones. This study compares variation and association in length among metapodials using 277 adult skeletons of Canis latrans. Canis latrans has a short, "functionless" first metacarpal (mc1) and "rudimentary, vestigial" first metatarsal (mt1). Results show that among the 10 metapodials, mt1 has the highest variation in length; other metapodials do not differ significantly from one another in their variation. Correlation coefficients for length of mc1 and mt1 with their ipsilateral metapodials 2-5 are significantly lower than coefficients for all other ipsilateral pairs. The correlation coefficient between left and right mt1 is significantly the lowest among all bilateral pairs of metapodials. Results are interpreted as follows. Mt1's high variation and low association in length are the outcome of less intense stabilizing selection pressure compared with other metapodials. The nonsignificant difference for variation in length between mc1 and metapodials 2-5 may be that mc1 is functional for development of a pollical dewclaw that helps restrain small prey.