Meeting Abstract
P1.52 Tuesday, Jan. 4 Development and evolution of varition in the autopod KEMP, AD*; THORINGTON, JR, RW; JERNVALL, J; Univeristy of Helsinki; Smithsonian (NMNH); Univeristy of Helsinki addisonkemp@gmail.com
The development and evolution of variability in the autopod Developmentally associated variability in teeth has previously been linked to evolvability. This study aims to examine a potentially similar pattern in the mammalian autopod. We took digital x-rays of over 1,500 mature specimens representing 52 species in 13 genera of Marmotini (Sciuridae). The lengths of all metapodial and phalangeal bones were digitized and coefficients of variation calculated. Variability was analyzed along two primary developmental axes of the limb. A trend toward increasing variability was found moving outward along the proximodistal axis; however no such trend was found along the anterior-posterior axis. Rather, anterior-posterior variability was found to correlate roughly to the order in which the cartilage models of the digit rays condense. The elements that vary most between individuals are the same that exhibit the greatest variability between species. This correlation may indicate that the increased variability found at the individual level facilitates the evolution of specific morphological diversity at the species level. These most-variable elements are also generally the distal-most ones in each digit, which may make the distal phalanges the most easily evolvable. This pattern relates well to Spermophilopsis leptodactylus, a sciurid noted for having highly elongated digits and claws. This increase is achieved by a general lengthening of all elements; however the greatest relative increases in length are found in the distal phalanges which, based on species and individual variability, may be the most highly evolvable. This work is supplemented by developmental studies in mice. Cartilage condensations were measured in embryos from e13 on and morphological measurements were taken in neonates and juveniles to determine when during development the observed patterns of variability become established.
