Caroline Williams

2016 Hellman Fellow

Assistant Professor, Integrative Biology
UC Berkeley

Project Title: Balancing supply and demand: modulation of energy efficiency during life history evolution


Animals experience different energy demands over the course of their lifecycle, depending on whether they are reproducing, having high levels of activity, or growing energetically expensive tissues. Energy supply also fluctuates according to resource availability in the environment. Thus, balancing energy supply and demand can be a major challenge. Energy metabolism itself carries costs in the form of reactive oxygen species (ROS) – damaging chemical byproducts of metabolism that can decrease health and longevity if produced in excess. The efficiency of mitochondrial metabolism can be adjusted to mitigate ROS production: less efficient metabolism, which results in a lower yield of energy for nutrients consumed, also results in lower ROS production. Therefore, if nutrients are abundant and energy demands low, animals should run at less than maximal efficiency.

Animals from humans and penguins to insects routinely run at less than maximal energy efficiency, suggesting that mitochondrial metabolism may be adjusted to balance energy supply and demand against the production of ROS. However, the extent to which energy efficiency can diverge as a result of life history evolution is still an open question. This project aims to establish, for the first time, the degree to which energy efficiency changes during the varying energy demands of an animal’s lifecycle, and as a component of life history evolution. We hypothesize that modulation of energy efficiency is an essential component of life history evolution. To test this hypothesis, we will use a cricket species that has two distinct morphs with highly divergent life history characteristics. Field crickets, like many insects, have alternate morphs that are specialized for dispersal flight or reproduction during early adulthood, activities with vastly different energetic demands occurring at different points in the lifecycle. These divergent energy demands are likely to be accomplished by differences in energy efficiency, making this an ideal study system in which to explore the relationship between life history traits and energy efficiency. In crickets specialized for flight versus reproduction, we aim to determine how life history specialization for dispersal versus reproduction impacts energy efficiency throughout the lifecycle and during the day, and to assess flexibility of energy efficiency in response to variation in nutrient supply and energy demand in dispersal and reproductive morphs. This work will uncover the degree to which life history evolution is associated with modulation of energy efficiency, potentially adding a new dimension to our understanding of life history trade-offs.

“This Hellman Fellowship has provided my lab with the funding to procure an instrument that will allow the team to measure mitochondrial function in our own lab, enabling the team to collect the preliminary data necessary to get this idea funded by an external agency. Thank you to the Foundation for facilitating my research at this critical time!”