Canalization and developmental instability of the fetal skull in a mouse model of maternal nutritional stress

Abstract

Nutritional imbalance is one of the main sources of stress in both extant and extinct human populations. Restricted availability of nutrients is thought to disrupt the buffering mechanisms that contribute to developmental stability and canalization, resulting in increased levels of fluctuating asymmetry (FA) and phenotypic variance among individuals. However, the literature is contradictory in this regard. This study assesses the effect of prenatal nutritional stress on FA and among-individual variance in cranial shape and size using a mouse model of maternal protein restriction. Two sets of landmark coordinates were digitized in three dimensions from skulls of control and protein restricted specimens at E17.5 and E18.5. We found that, by the end of gestation, maternal protein restriction resulted in a significant reduction of skull size. Fluctuating asymmetry in size and shape exceeded the amount of measurement error in all groups, but no significant differences in the magnitude of FA were found between treatments. Convsersely, the pattern of shape asymmetry was affected by the environmental perturbation since the angles between the first eigenvectors extracted from the covariance matrix of shape asymmetric component of protein restricted and control groups were not significantly different from the expected for random vectors. In addition, among-individual variance in cranial shape was significanlty higher in the protein restricted than the control group at E18.5. Overall, the results obtained from a controlled experiment do not support the view of fluctuating asymmetry of cranial structures as a reliable index for inferring nutritional stress in human populations.

Analyzing Fluctuating Asymmetry with Geometric Morphometrics: Concepts, Methods, and Applications

“…A useful measure for this is the ratio of the respective mean squares in the Procrustes ANOVA, which is also the F ratio for the effect of fluctuating asymmetry [11,13]. Under favorable conditions, this ratio can be high (e.g., 25 in the example of Table 1, or also in published examples [44,56,93]), indicating that the measurement error makes up no more than a few percent of the estimate of fluctuating asymmetry and is therefore negligible. More often, however, this ratio is lower, with fluctuating asymmetry just a few times bigger than the error term, suggesting that replication and other measures to reduce the effect of measurement error are necessary.…”

Maternal Stress Affects Fetal Growth but Not Developmental Instability in Rabbits

“…Under this model, it is expected that developmental imprecision accumulates during the continued growth such that effects on foetuses will become expressed later in life [47]. Interestingly, skull shape FA in mice under nutritional stress did not increase in magnitude, but the spatial pattern of FA was altered [48]. Unfortunately, this aspect could not be studied here because we used linear FA measures.…”

“…Unfortunately, this aspect could not be studied here because we used linear FA measures. Future research should (also) focus on spatial/shape aspects of FA (see also [48]). …”

Morphometrics, 3D Imaging, and Craniofacial Development

“…Late fetal (Gonzalez et al 2014), Neonatal (Boughner et al 2008) ), and adult mouse landmark sets used in recent studies by our group.…”