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The Evolutionary History and Preservation of Melanins and Melanosomes

2018, Doctor of Philosophy, University of Akron, Integrated Bioscience.
Melanins are a class of ubiquitous pigments that provide not only coloration to the organisms in which they produced, but also serve as a mechanism for thermoregulation, protection from ultraviolet radiation and cytotoxicity induced by free radicals, as well as numerous other beneficial roles. In most animals, melanins are housed in organelles called melanosomes. Melanosome morphology correlates with melanin-based coloration in birds and mammals, but melanosome diversity is limited in basal amniotes. Approximately 10 years ago, the study of melanosomes, melanin, and coloration was extended to the fossil record by the reinterpretation of microbodies preserved in fossil feathers initially interpreted as bacteria as remains of melanosomes. However, despite countless lines of evidence for this hypothesis that have been described since, some authors argue that the bacterial hypothesis is equally parsimonious.

This dissertation will address some of the concerns of purveyors of the bacterial hypothesis and discuss the evolutionary history of melanosomes and melanins. We first tested the hypothesis that striped fossil feathers are the result of bacterial preservation through taphonomic experimentation. We found that modern keratinolytic bacteria preferentially colonize unpigmented stripes in modern feathers over melanized stripes, so it is unlikely that this hypothesis was supported in ancient ecosystems. We also found that bacteria and biofilms preserved in association with fossil integument are dissimilar to microbodies interpreted as fossil melanosomes.

We began the second part of this dissertation by describing an enantiornithine bird that exhibits a mix of juvenile skeletal characteristics and sexual ornaments. Melanosomes preserved in its feathers are similar in morphology and arrangement to those in modern iridescent feathers, which are predominantly used to attract mates. We also described melanosomes associated with the fossilized skin of amphibians and lampreys, which do not exhibit diverse melanosome morphologies. Convergent shifts in melanosome diversity in mammals and pennaraptoran dinosaurs may have occurred due to changes in physiology between these two groups and their ancestors. Finally, we reviewed the functions of melanins in modern organisms and evidence for these functions in the fossil record. Based on their modern ubiquity, we hypothesized that melanin may have evolved early in the history of life.
R. Joel Duff, Ph. D. (Advisor)
Matthew Shawkey, Ph. D. (Committee Member)
Liliana D'Alba, Ph. D. (Committee Member)
Julia Clarke, Ph. D. (Committee Member)
John Senko, Ph. D. (Committee Member)
200 p.

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Peteya, Jennifer. "The Evolutionary History and Preservation of Melanins and Melanosomes." Electronic Thesis or Dissertation. University of Akron, 2018. OhioLINK Electronic Theses and Dissertations Center. 19 Sep 2018.

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Peteya, Jennifer "The Evolutionary History and Preservation of Melanins and Melanosomes." Electronic Thesis or Dissertation. University of Akron, 2018.


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