Graduation Year

2021

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts

Department

Biology

Second Department

Computer Science

Reader 1

Findley Finseth

Reader 2

Danae Schulz

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Terms of Use for work posted in Scholarship@Claremont.

Rights Information

© 2021 Fiona M Callahan

Abstract

Multiple mammalian lineages have independently evolved to both marine and subterranean environments, and yet mammals in each of these extreme environments exhibit convergent similarities, including genes related to muscle physiology. The muscle protein titin, encoded by the gene TTN, is much less conserved than other fundamental muscle fiber proteins. This suggests titin as a key contributor to physiological diversity across mammalian muscles. Large deletions were previously found in a variable region of TTN, called the PEVK region, in several marine mammals and one subterranean mammal.

Here, we test the hypothesis that titin evolved convergently in response to novel environmental challenges posed by marine or subterranean environments by 1) testing for differences in TTN structure in the PEVK region and 2) investigating evolutionary rate on branches after habitat change. We find no evidence that the overall structure (number of exons or total exon length) varies significantly by habitat. Additionally, we find no evidence that the evolutionary rate of a subset of conserved PEVK exons is significantly different after the divergence into marine or subterranean environments. Therefore, differences seen in muscle physiology in these mammals may not originate in this genomic region, or they may be more subtle than originally predicted. We also find that the number of exons found changes dramatically with the quality of genomic sequences. Therefore, higher-quality genomic sequences will be needed to fully resolve differences in repetitive genes such as titin.

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