Abstract
Genotypic variation, environmental variation, and their interaction may produce variation in the developmental process and cause phenotypic differences among individuals. Developmental noise, which arises during development from stochasticity in cellular and molecular processes when genotype and environment are fixed, also contributes to phenotypic variation. While evolutionary biology has long focused on teasing apart the relative contribution of genes and environment to phenotypic variation, our understanding of the role of developmental noise has lagged due to technical difficulties in directly measuring the contribution of developmental noise. The 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 variation in the component of the developmental process corresponding to environmental and genetic factors (here treated together as a unit called the LALI-type) 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 variation in the LALI-type 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, variation in color pattern due to LALI-type variation exceeds that due to developmental noise in the studied gecko cohort. However, the effect of developmental noise on patterning is also substantial. Our approach addresses one of the major goals of evolutionary biology: to quantify the role of stochasticity in shaping phenotypic variation.
Highlights
A first-order approximation of phenotypic variation is that genotype and environment variation maps to phenotype variation
We found that for our cohort, the proportion of phenotypic variation due to variation in the unit composed of genotypic and environmental variation is larger than that due to developmental noise
For each of the two local activation and long range inhibition (LALI) models we considered, we found that the resulting phenotype clouds for each of the phenotypes did not all overlap (Fig 10) indicating that developmental noise alone cannot explain the variations among the phenotypes
Summary
A first-order approximation of phenotypic variation is that genotype and environment variation maps to phenotype variation. At the developmental level, genotypic (developmental program) and/or environmental changes, or stochastic variation can generate developmental variation This stochastic variation, called developmental noise, is the difference in phenotypic outcomes that occurs when genotype and environment are fixed (e.g.,[5,6,7]), due to stochasticity in cellular and molecular processes [4, 6]. The interaction of these sources of variation (genotype, environment, and stochasticity), combined with the sheer magnitude of the number of phenotypic variables, makes the study of the phenotypic variation of a population extremely complex. We do not analyze each component (genotype, environment, developmental noise) of the developmental process alone, but we use different fixed combinations of genotype and environment taken together (each one of them called LALI-type, see below and Table 1) versus developmental noise to estimate the influence of variation in LALI-type and developmental noise on phenotypic variation
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