Embryological origins of developmental stability: size, shape and fluctuating asymmetry in prenatal random bred mice

Ontogenetic patterns of fluctuating asymmetry (FA) can be used to test models for the mechanisms underlying stability during embryonic development (developmental stability). In this study, we ask whether developmental processes initially show high levels of instability that are subsequently dampened through active compensatory mechanisms or passive properties of developmental systems or whether the effects of instability accumulate during embryonic development causing random drift away from an earlier stable state. Previous work on this question has dealt with postnatal skeletal growth and thus been unable to effectively distinguish developmental instability from the effects of mechanically mediated variation in bone modeling and remodeling. Here, we report that FA variances of limb skeletal elements in CD1 mice decrease with gestational age from day 14 to birth (day 20.5). Thus, in mouse limbs, skeletal development is characterized by a high level of developmental instability initially that is reduced during subsequent prenatal development. These results are consistent with the existence of active mechanisms that compensate for the effects of minor perturbations or deviations during development. However, they are also consistent with Soule's model of allomeric variation in which the variance of structures is reduced as the number of independent developmental events that produce them increases. This study illustrates that predictions based on morphometric analyses can yield insights into general properties of developmental systems in cases where specific developmental mechanisms are not yet known.