Unlike mice and humans, basal vertebrates such as sharks and fish exhibit continuous tooth renewal and thus offer an attractive model for studying tooth replacement. Here, by taking advantage of the natural variation in threespine stickleback fish populations, Craig Miller and colleagues examine the genetic and developmental basis of tooth regeneration (p. 2442). They first compare the tooth morphology of three laboratory-reared populations: one marine population and two freshwater populations. They report that, relative to the ancestral marine population, the two freshwater populations exhibit increased numbers of pharyngeal teeth, increased tooth plate areas and decreased intertooth spacing. The increase in tooth number, they demonstrate, occurs late in development and is due to an elevated rate of tooth replacement. When comparing the two freshwater populations, the researchers further note that the spatial patterning of newly formed teeth and the timing of their emergence differ between the two populations, suggesting that they use distinct developmental mechanisms. Finally, using quantitative trait loci mapping, the researchers show that different genomic regions contribute to the increase in tooth number in the two freshwater populations. These findings support a model for convergent evolution via distinct developmental routes and provide insights into the genetic factors that govern tooth replacement.
- © 2015. Published by The Company of Biologists Ltd