Meeting Abstract

56.6  Jan. 6  Evolution of murine dentitions along the path of least developmental resistance KAVANAGH, KD*; EVANS, A; JERNVALL, J; University of Helsinki, Finland; University of Helsinki, Finland; University of Helsinki, Finland kathryn.kavanagh@helsinki.fi

We report discovery of a developmental rule governing relative molar sizes
in the mouse Mus musculus, and, by a macroevolutionary test, we
demonstrate its success in predicting the range of dentition patterns
found among murine rodent species varying in diet, thereby providing an
example of ecologically-driven evolution along the path of least
developmental resistance.This study first examined relationships between
sequentially developing molars in the mouse by simple experimental surgery
to separate tooth germs.We cultured tooth germs from a mutant mouse that
expressed Green Fluorescent Protein off a Sonic Hedgehog promoter, which
marked the enamel knots and pinpointed the future positions of the molars
and cusps in vitro, thereby allowing us to follow sequential organogenesis
of molars in individual teeth. The results suggested an inhibitory
patterning cascade guiding development such that the size of each
subsequent tooth was related to the relative size of the preceding tooth.
To test the role of the inhibitory patterning cascade in evolution, we
measured crown areas of individual molars from 3D scans of dentitions from
25 species of murine rodents. We found that the developmental rule
predicted the macroevolutionary pattern shown among rodent species, and
that the dietary pattern of the species appeared to drive the evolutionary
shift in relative molar sizes.