Conclusions

The proportion of environmental variance identified through fluctuating asymmetry was relatively small (11.0%-28.5% of the total variance), implying that heritabilities (h²) of tooth shape range from 0.71 to 0.89. These h² values are somewhat higher than in previous studies of heritability in dental characters, but not surprisingly so. Leamy and Bader (1968) found h² values that ranged between 0.60 and 0.66 for the linear size of field mouse molars. Hlusko and Mahaney (2003) found h² to be as high as 0.725 for the presence of cingular remnants in baboon molars, though in most cases h² was around 0.60 for that trait.

While the differences between contralateral teeth are often as great as between individuals of the same species, they were much, much smaller than differences between species (Figure 7). In Arvicola terrestris the maximum Procrustes distance between teeth from two sides of the same individual was 0.015 units. The mean distance between teeth belonging to different species was nearly an order of magnitude greater at 0.095 units.

Arvicoline rodents may have especially variable teeth, and they may vary within species and between species, but the magnitude of variation between species is so much greater than that within species that variation is not likely to confound palaeontological interpretations. The amount of ecophenotypic environmental variance within the species we measured appears to be negligible compared to the differences we observed between species.