Energy management and life history evolution in variable environments

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The energetic status of an individual is hypothesized to be a core influence on its reproductive output, but energetic measurements are typically made in laboratories, far removed from their eco-evolutionary context. My long-term goal is therefore to understand how environmental variation influences the energetic statuses of, and shapes the reproductive allocation decisions made by, wild animals. I will meet three short-term objectives over this granting cycle: (1) Determine the environmental and intrinsic influences on variation in levels of energy acquisition and assimilation in preparation for reproduction; (2) Test two hypothesized energetic mechanisms put forward to explain reproductive constraints during a single breeding event; and (3) Uncover relationships between breeding events that explain optimal energy allocation decisions across the lifetime. I will use a state-of-the-art mobile laboratory to characterize the energetic statuses of individuals within two established wild mammal study systems (the Rocky Mountain Ground Squirrel (RMGSP) and Kluane Red Squirrel Projects (KRSP)) as well as a new field study on Arctic ground squirrels (Urocitellus paryii) and a captive study on lab mice (Mus musculus). Specifically, I will use a quantitative magnetic body composition analyzer to measure energy stores (fat and lean mass) and open flow respirometry to measure energy use (metabolic rate). In the field projects, we will collect complete life history data for all individuals in fully censused populations against a backdrop of quantifiable environmental variation. In RMGSP, we will study the influences of natural and manipulated variation in food resources and weather on hibernation profiles and reproductive allocations of Columbian ground squirrels (U. columbianus). We will also collect detailed energetic data during hibernation of individuals from two different elevations in a common, captive environment. I will evaluate the generality of these findings by conducting a parallel study on wild Arctic ground squirrels. In KRSP, we will assess the determinants of variation in cached and on-body resources, and how this variation influences reproductive allocations made within and across breeding events in red squirrels (Tamiasciurus hudsonicus). We will also use a fur reduction experiment to test the hypothesis that limits on dissipating extra metabolically generated heat during reproduction can constrain output. In lab mice, I will study the interactive effects of fur reduction and calorie restriction on longevity and reproductive output. Variation in reproductive output is a central component in both population and microevolutionary dynamics, but a main contributor to this variation (energetic status) is typically treated as a black-box'. By opening this black box, this research should produce results of both important fundamental and applied relevance.