Hibernacula and hormones of an endangered jumping mouse

Zahratka, Jennifer Lynn (2023) Hibernacula and hormones of an endangered jumping mouse. Doctoral thesis, Northern Arizona University.

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Abstract

In seasonal environments, animals must adjust their behavior and physiology to balance energetic demands. The strategies animals use to balance energy demands and adapt to seasonally changing environments determines their survival and fitness. Among these strategies, hibernation is an evolutionary adaption to cope with seasonally available resources that is marked by dramatic physiological and behavioral adjustments affecting fitness, reproduction, and phenology of life histories. Hormones serve as chemical messengers to translate perceived environmental signals into behavioral and physiological adjustments. In my dissertation, I provide insight into the hibernation strategy among one of the smallest, nonvolant terrestrial hibernators, the New Mexico meadow jumping mouse (Zapus luteus, formerly Zapus hudsonius luteus) and the role of hormones in making seasonal adjustments, specifically during reproduction and the onset of hibernation. The lack of data on this federally Endangered species limits our understanding of how it adjusts to fluctuating environmental conditions. To address this, I first sought to describe hibernacula (unconfirmed for this species) and developed methods and criteria to identify them. Once a hibernaculum was confirmed, I measured soil temperatures at 3 depths within 3 m of each hibernaculum as an approximation of temperatures in the hibernaculum. I compared these soil temperatures to those to collected at randomly selected sites located within 500 m of the hibernaculum in potential habitat. I also collected aspect, slope, horizontal and canopy cover, elevation, and depth of the underground burrow to describe each hibernaculum. I found New Mexico meadow jumping mice favored sites for hibernacula with north-facing aspects and some vegetation cover. Proximity to water varied but averaged 59.6 m ± 19.6 (standard error; SE). New Mexico meadow jumping mice dug hibernation burrows at an average depth of 29.5 cm ± 2.4. Soil temperatures at this depth were cold in winter (x̅ = 1.0°C ± 0.01 from December through February) and relatively consistent (CV = 118% at 30 cm depth) compared to other depths (CV = 163% at 10 cm and 37% at 50 cm). Soil temperatures near hibernacula were colder and warmed later in spring than randomly selected comparison sites. Females selected hibernacula where soil temperatures were colder (x̅ = 2.1 °C ± 0.03) than hibernacula of males (x̅ = 2.5 ± 0.02; W = 230944353, p < 0.0). New Mexico meadow jumping mice presumably constructed hibernacula at sites cold enough to reduce body temperature and maximize metabolic savings, but not so cold that they catabolized all their fat reserves to maintain their set body temperature. We assume females selected colder hibernacula than males because it conferred an energetic advantage that females needed compared to males. In my second study, I addressed the capacity for New Mexico meadow jumping mice to reproduce more than once during an active season. Reproduction is an energetically demanding annual life cycle event so that animals must balance energetic demands with the tradeoffs between survival and reproduction. Further, the timing of reproduction and potential number of young produced during the active season by this species is unknown. The fecundity of this Endangered species is important to its recovery. Using enzyme immunoassays on fecal samples collected from captured females (n = 75), I quantified progesterone levels, the pregnancy hormone, coupled with physical condition of captured females, to determine pregnancy. We found fecal progesterone metabolite (FPM) levels from pregnant animals were highest in July (x̅ = 1000.1 pg/mg ± 142.7). We used the range of mean FPM levels when jumping mice are not known to reproduce in September (224.0 pg/mg ± 86.2) and October (122.4 pg/mg ± 74.0) as our baseline. We used both months because no animals were captured in Arizona in October due to the onset of hibernation. Based on these fecal progesterone metabolite levels, I found New Mexico jumping mice reproduced only once, most commonly in July. I also found differences in fecal progesterone metabolites between states (i.e., study areas) suggesting more females were pregnant in Arizona than Colorado. Finally, I used glucocorticoids (cortisol) and thyroid hormones (T3) coupled with body mass and the predictable timing of life events as tools to identify energetically demanding periods during the active season. Glucocorticoids and thyroid hormones are primarily responsible for mediating the trade-offs in energy modulation between predictable annual life events. Reproduction and the pre-hibernation period, specifically, are characterized by changing energetic demands. I found New Mexico meadow jumping mice showed variations in cortisol and T3 metabolite levels consistent with the onset of hibernation in fall, but not reproduction. These data suggest the pre-hibernation period was the most energetically demanding period during the active season. I also found lower levels of fecal T3 metabolites in Colorado than Arizona and higher cortisol in Colorado than Arizona, suggesting phenotypic plasticity to environmental conditions (e.g., elevation, moisture regimes, vegetation, latitude). These data will facilitate informed conservation measures for recovery of this species and provide a platform for future research on hibernation physiology.

Item Type:	Thesis (Doctoral)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	conservation; hibernation strategu; hormones; New Mexico Jumping Mouse; Zapus luteus; Hibernation physiology
Subjects:	Q Science > QL Zoology
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Forestry
Date Deposited:	07 Aug 2026 17:58
Last Modified:	07 Aug 2026 17:58
URI:	https://openknowledge.nau.edu/id/eprint/6340

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