Display Full Text | Download Full Text
1.45 MB PDF file

Degree

Doctor of Philosophy, Case Western Reserve University, Biology, 2009.

Abstract

The success of the Modern Synthesis has resulted in forces of evolutionary change other than natural selection being marginalized. However, recent work has attempted to show the importance of non-selective influences in shaping organic form. One such force is developmental bias, the differential produced of phenotypes. I use a simulation model of neural development to explore questions of general interest about developmental systems. From an analysis of the bias in the production of phenotypic variants in the developmental model, I find the pattern of developmental bias varies strongly with the genotype even among phenotypically-neutral genotypes. In addition to this genotype-dependent developmental bias (local bias), an intrinsic bias exists in the developmental system (global bias). I also show that developmental bias varies among related genotypes that produce the same phenotype. Finally, I illustrate how a pattern of bias emerges from the manner in which mutations affect the regulatory structure of the wild-type genotype. These results suggest that developmental bias could have a strong influence on the direction of evolutionary modification. In subsequent analyses exploring the interaction of developmental bias and selection during adaptive evolution, I find developmental bias guides phenotypic transitions with the result that multiple phenotypic pathways are taken towards the target phenotype across simulations. I also find higher-fitness phenotypes often become accessible with the accumulation of selectively-neutral mutations. The change in accessibility is due to alterations of the regulatory structure of the genotypes through the neutral mutations. This lability of developmental bias recommends a comparative approach to the experimental investigation of bias in natural systems. The alteration of phenotypic accessibility following the accumulation of neutral mutations can be conceptualized as a population moving along a network of isofitness genotypes linked by mutations (neutral networks). The phenotypes produced by non-fitness-neutral neighbors of the neutral genotypes are likely to vary as the population moves to different regions of the network. These networks are created by the mutational operator and the degeneracies of the dual mappings of genotype to phenotype and phenotype to fitness. Topological properties of the neutral networks could lead to insights into the impact on evolvability of developmental systems.

Subject Headings

Biology

Keywords

evo-devo; developmental constraint; developmental bias; neutral networks

Committee / Advisors

Randall Beer, PhD (Committee Chair)
Radhika Atit, PhD (Committee Member)
Patricia Princehouse, PhD (Committee Member)
Robin Snyder, PhD (Committee Member)
Mark Willis, PhD (Committee Member)

Pages

89p.

Document number: case1232655232
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=case1232655232

This ETD has been downloaded 233 times (through March 2013)