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Author ORCID Identifier
Open Access Dissertation
Doctor of Philosophy (PhD)
Organismic and Evolutionary Biology
Year Degree Awarded
Month Degree Awarded
R Craig Albertson
Evolution | Integrative Biology
Phenotypic constraints are ubiquitous throughout nature, being found throughout all stages of life and at multiple different biological levels including cellular, genetic, environmental, behavioral, evolutionary, and developmental. These constraints have shaped, not only the natural world, but the way that we perceive what is possible, or impossible, an observation made clear by François Jacob in his 1977 paper “Evolution and Tinkering”. This is reflected in the literature, repeatedly, by the regular occurrence of densely packed visualization of phenotypic space that seemingly always have large areas that go unoccupied. Despite constrained regions of space being observable across countless taxa, identifying the mechanisms of those constraints remains elusive. Given that constraints are widespread and have influenced how evolution may work, my aim was to identify mechanisms of constraint throughout multiple biological levels. Chapter one is divided into two parts, sections A and B, but largely focuses on how constraints are influenced by genetics. For this, we investigated crocc2, a protein that encodes for a structural component of the ciliary rootlet which in turn plays a major role as a mechanosensory for nearly all cells. We found dysfunctional crocc2 resulted in both dysmorphic bone development and a decrease in the plastic response potential of zebrafish (section A), as well as altered developmental trajectories in juvenile morphology, presumably due to alterations in cellular polarity and inadequate extracellular communication. Importantly, all results from this chapter point toward crocc2 play a canalizing role in the production of phenotypes at multiple life-history stages. Chapter 2 takes a different approach into understanding constrains by looking at broad ecological alterations and how those alterations may alter morphology of resident taxa. Here, we utilized the heavily altered habitat of the Tocantins River in the Amazon and the existing museum collections to evaluate how select representatives of the cichlid community had responded to such change. We found significant changes in contemporary morphology across all included cichlid species compared to their historical counterparts. These data show that alterations to the environment have resulted in changes to the local resident species, and possibly an alteration to their future evolutionary trajectories. Among the species included, one was found to have the most substantial morphological changes, which is what we followed up in the next chapter. Chapter 3 dug into the morphological changes of Satanoperca, a Geophagine cichlid with a unique feeding mechanism known as winnowing. Winnowing is a poorly understood mechanical process involving substrate manipulation. Given that anthropogenic alterations to local hydrology oft result in changes to the benthic sediment composition, we wanted to know if differing substrates was enough to induce a plastic response in winnowing fishes, and if so which traits were effected. We found significant differences across our experimental populations in both shape and disparity and present evidence in support of wide-spread integration across craniofacial traits. In addition, these data suggest that the novel anatomical structure, the epibranchial lobe, is more modular than other craniofacial traits involved in the winnowing process. Chapters 4 and 5 utilize a unique lineage of fishes, the Bramidae, to understand how developmental and evolutionary constraints are broken to produce morphological novelties. We used a combination of DNA sequences from GenBank and numerous museum specimens to illuminate constraints and determine how constraints are broken to produce complex phenotypic novelties. In Chapter 4, we found that the fanfishes had experienced greater rates of morphological evolution than other members of the Bramidae family, resulting in their occupation of an entirely novel region of phenotypic space. In Chapter 5, we elaborated on this by investigating the developmental processes involved in producing an extreme morphological novelty. The data presented in Chapter 5 provide evidence suggesting that the fanfishes have broken various constraints, resulting in prominent anatomical and morphological changes to accommodate their novel phenotype. In all, my dissertation provides examples of how constraints have shaped the variability that we see throughout life and shows examples of how constraints can be identified, what happens when they are broken, and how they work to control the pace and trajectory of evolutionary processes.
Gilbert, Michelle, "CONSTRAINTS OF THE IMAGINATION: HOW PHENOTYPES ARE SHAPED THROUGH GENETICS, THE ENVIRONMENT, AND DEVELOPMENT" (2022). Doctoral Dissertations. 2622.
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