Title:

Intrinsic and extrinsic drivers of brown lemming stress hormone levels in Utqiaġvik, Alaska

Arctic rodents often exhibit dramatic, yet regular (3-4 year) cycles in population density. Hypotheses attribute cyclicity to both extrinsic (e.g., predators, food, weather) and intrinsic (e.g., physiology, genetics, behavior) factors, the relative roles of which are debated. Here we explore the relationship between stress and cyclicity for brown lemmings (Lemmus trimucronatus) in Utqiaġvik (formerly Barrow) Alaska. Stress hormones (cortisol and corticosterone) are critical for allowing animals to cope with changes and challenges in their environment and can affect individual survival and reproductive success. Using hair collected twice a year (at snowmelt and peak green up) over a 5-year period (2018-2022) we assess whether lemming stress hormones (corticosterone) reflect changes in population density, predator density, or environmental conditions. We used capture mark recapture surveys to generate density estimates, NOAA weather station data and a NEON snow camera to characterize environmental conditions. We found significant intrinsic effects of age, sex, and reproductive status on stress hormone levels. Summer temperature was positively and winter temperature was negatively associated with hormone levels. Of interest, we found a positive relationship between stress hormones and lemming density, but not with cycle phase. Understanding which factors drive rodent populations and how these dynamics might change with warming is essential for predicting the impacts of climate change on arctic ecosystems as herbivore pressure shapes plant community composition, soil nutrient availability and carbon concentrations.

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