Date of Award

12-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Statement

Doctor of Philosophy in Biological Sciences

Department

Department of Biology and Wildlife

Granting Institution

University of Alaska Fairbanks

Committee Chair

O'Brien, Diane

Committee Member

Hansen, Cristina

Committee Member

Kielland, Knut

Committee Member

Muscarella, Mario

Table of Contents

Chapter 1: General introduction

Chapter 2: The distinct amino acid carbon isotope fingerprint of obligate anaerobic bacteria allows estimation of gut bacteria as protein sources for herbivorous mammals

Chapter 3: Carbon isotope ratios of amino acids estimate the seasonal contribution of rumen bacteria as a protein source to moose

Chapter 4: Amino acid δ15N values predict severe underweight status in a captive population of muskoxen

Chapter 5: General conclusions

Abstract

Knowing how large herbivorous mammals acquire nutrients is critical to understanding how they can survive and reproduce in seasonally nutrient-limited landscapes. Gut bacteria and other microorganisms in herbivores digest plant fiber, providing energy, and potentially protein. In my first data chapter, I evaluated the importance of dietary and gut microbial protein to herbivores with different digestive physiologies using carbon isotopes of essential amino acids as markers of protein source. Foregut fermenters, moose (Alces dices) and muskox (Ovibos moschatus), and a hindgut fermenter with coprophagy, snowshoe hares (Lepus americanus), derived half of their protein from gut bacteria, whereas horses (Equusferus caballus), a hindgut fermenter, derived one-third. In my second data chapter, I evaluated how protein sources for moose change seasonally between summer, when plant quality is highest, and winter, when plant quality is lowest. Moose used nearly equal protein from plants and rumen microbes (bacteria and fungi) in summer but increased their use of rumen microbes in winter. Gut bacteria are an important source of protein to both foregut and hindgut fermenters and provide additional protein to moose when forage quality is lowest. In my final chapter, I proposed and evaluated a novel measure of body condition in muskoxen. Body condition is central to animal health and fitness but can be difficult to assess in free-living animals. I evaluated the δ15N values of amino acids to predict underweight status in muskoxen that underwent severe loss of body mass due to a trace mineral deficiency. δ15N values of glutamate/glutamine and leucine predicted underweight status, in combination with aspartate/asparagine and serine in females and proline in males. In contrast, bulk δ15N values had no relationship with underweight status. δ15N values of amino acids are potentially a useful tool to evaluate body condition in free-living animals.

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