Year of Award

2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Organismal Biology, Ecology, and Evolution

Department or School/College

Division of Biological Sciences

Committee Chair

Zachary A. Cheviron

Commitee Members

Creagh W. Breuner, Brandon S. Cooper, Jeffery M. Good, Winsor H. Lowe

Keywords

bergmann's rule, body composition, fat mass, high elevation, peromyscus maniculatus, thermogenesis

Publisher

University of Montana

Abstract

Body composition, the percent of lean and fat mass, is a snapshot of an individual’s energetic state at a moment in time. Wild organisms should allocate energy to optimize fitness, so tracking changes in body composition provides a window into how priorities may shift throughout the year or across environments. While seasonal variation in body composition is wellcharacterized in systems such migrating birds (Scott et al. 1994) and hibernating mammals (Hellgren 1998), much less is known about how this trait varies across species ranges and thus how organisms modify their body composition and to meet local environmental challenges. For my dissertation I investigated the relationship between body composition and environmental variation, genetic background, and survival in the wild.

In my first chapter I surveyed deer mice at thirty sites along a 4000-meter elevational transect to quantify variation body composition and determine if the species follows Bergmann’s rule. While the phenomenon of increasing body size at higher latitudes is well documented, there are fewer tests across elevational gradients, and it is unknown whether species that follow Bergmann’s rule preferentially add fat or lean mass. Deer mice conformed to Bergmann’s rule, increasing mass with elevation, but body composition did not change as fat and lean mass increased in equal proportion.

For my second chapter I used an acclimation experiment to tease apart the effects of temperature and hypoxia on variation in body composition and thermogenic capacity in two populations of captive deer mice. Highland mice were able to attain greater hypothermia resistance than lowlanders in the combined cold and hypoxia treatment, while also adding less lean mass over the course of the acclimation.

Body composition is often quantified using condition indices, which are then used to assess individual health and habitat quality. Although the role of fat stores in reproduction is welldocumented, there are few tests of the association between condition and survival. In my third chapter I used two-year mark-recapture experiment to quantify the effect of condition and body composition on survival. I documented significant variation in body composition and survival between sites, but in this case the “snapshot” of fat and lean mass did not affect future survival.

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© Copyright 2023 Cole Joseph Wolf