ZELDITCH, ML*; MYERS, P; LUNDRIGAN, BL; Univ. of Michigan, Ann Arbor; Univ. of Michigan, Ann Arbor; Michigan State Univ., E. Lansing: Dietary consistency and the canalization of skull growth

Forces generated by biting and mastication influence mammalian skull shape and are also thought to influence its variability. As a result, eating soft food reduces growth, and reportedly alters skull proportions and elevates craniofacial variability. However, even dramatic differences in dietary consistency might have little or no impact on skull shape, as we found in a prior analysis of deer mice (Peromyscus maniculatus bairdii) who were fed either hard laboratory chow or a gruel made from that chow. To explain that lack of impact, we postulated that these active animals, observed to gnaw their cages and bedding, might thereby compensate for any reduction in forces generated by feeding. If that is the case, we might expect that eating soft food would have no impact on skull variability either. However, that nonnutritive compensatory gnawing might be fairly idiosyncratic, and therefore fail to maintain the normally low level of variance. To determine if variance is any more affected by diet than the average skull form, we first reanalyze the impact of diet on that average, taking advantage of recent progress in morphometrics, and then compare variance in skull size and shape. We confirm diet has no significant effect on average skull shape, but it does have a very slight impact on size, at least in ventral view; skulls of the hard-diet group are larger in ventral view (albeit by only 2.5%). Contrary to expectations, the group fed hard chow is more, rather than less variable, in skull size, but, as expected, is less variable in skull shape. Taken together, that greater variability in skull size and lesser variability in skull shape, suggests that the forces generated by biting and mastication effectively canalize skull shape even in the face of elevated variation in size.