ORCID
0000-0003-2715-8759
Date of Award
2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biology
First Advisor
Melissa Pespeni
Abstract
The well-known quote, "It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is most adaptable to change." - ironically misattributed to Charles Darwin and itself a product of gradual modification over time - perfectly captures the essence of evolutionary biology. The environment, along with the populations inhabiting it, are in a state of continual change. When the same environmental change occurs repeatedly, different strategies can evolve to maximize long-term fitness. The type of strategy that evolves is heavily dependent on the features of such environmental change and typically involves the heritable bias of phenotypic variation - both its magnitude and shape. For example, organisms can change their phenotypes in response to an environmental cue (phenotypic plasticity), have an in-between phenotype, or a diverse set of offspring to minimize the risk of maladaptation upon a sudden change in the environment (bet-hedging). Furthermore, the phenotypic variation available to natural selection can be biased by a genotype-to-phenotype map that produces the new adaptive phenotype in fewer mutational steps and by chromosomal inversions that locally reduce the rate of recombination and therefore keep specific combination of alleles together in the population.
In this dissertation, I present research that investigates when and how phenotypic variability evolves in response to adaptation in variable environments using sequence analysis of natural populations and computational modeling. Research involving the purple sea urchin, Strongylocentrotus purpuratus, sampled along a broad latitudinal gradient uncovered potential genetic variants involved in local adaptation to pH variability (Chapter 1), along with putative inversion polymorphisms maintained by balancing selection (Chapter 2). In parallel, computational models of evolving genotype-to-phenotype maps showed that the kind of phenotypic variability that evolves is heavily dependent on the frequency of environmental change, the strength of selection, and the mutation rate that the populations experience (Chapter 3). In addition, the shape of the varying fitness landscapes was found to have an important effect on measures of evolvability and the maximum fitness the populations could reach, while average fitness, robustness, and genotype-space exploration were increased consistently in variable environments (Chapter 4).
Thus, my Ph.D. work presents real-world examples of adaptation to environmental variability, and sheds light on features of environmental variability that have an important influence on the kind of phenotypic variability that evolves. The speed and direction of evolution after a change in the environment is heavily dependent on the existence of, and the propensity for phenotypic variation. Therefore, this research may help advance our understanding of modern challenges such as adaptation to antimicrobials and to climate change across the globe.
Language
en
Number of Pages
176 p.
Recommended Citation
Petak, Csenge, "Exploring the effects of environmental variability on adaptation and phenotypic variation in sea urchins and simulations" (2025). Graduate College Dissertations and Theses. 2035.
https://scholarworks.uvm.edu/graddis/2035
