Isolating and Quantifying the Role of Developmental Noise in Generating Phenotypic Variation
Phenotypic variation in organisms is typically attributed to genotypic variation, environmental variation, and their interaction. Developmental noise, which arises from stochasticity in cellular and molecular processes occurring during development when genotype and environment are fixed, also contributes to phenotypic variation. The potential influence of developmental noise is likely underestimated in studies of phenotypic variation due to intrinsic mechanisms within organisms that stabilize phenotypes and decrease variation. Since we are just beginning to appreciate the extent to which phenotypic variation due to stochasticity is potentially adaptive, the contribution of developmental noise to phenotypic variation must be separated and measured to fully understand its role in evolution. Here, we show that phenotypic variation due to genotype and environment, versus the contribution of developmental noise, can be distinguished for leopard gecko (Eublepharis macularius) head color patterns using mathematical simulations that model the role of random variation (corresponding to developmental noise) in patterning. Specifically, we modified the parameters of simulations corresponding to genetic and environmental variation to generate the full range of phenotypic variation in color pattern seen on the heads of eight leopard geckos. We observed that over the range of these parameters, the component of variation due to genotype and environment exceeds that due to developmental noise in the studied gecko cohort. However, the effect of developmental noise on patterning is also substantial. This approach can be applied to any regular morphological trait that results from self-organized processes such as reaction-diffusion mechanisms, including the frequently found striped and spotted patterns of animal pigmentation patterning, patterning of bones in vertebrate limbs, body segmentation in segmented animals. Our approach addresses one of the major goals of evolutionary biology: to define the role of stochasticity in shaping phenotypic variation.