Roeder, Diane

• Ph.D., Ecology and Evolutionary Biology, University of Oklahoma 

• M.S., Zoology, University of Oklahoma 

• B.S., Biology, Cameron University

Increasing global temperatures and variability in weather patterns are expected to significantly affect the

distribution, persistence, and behavior of a wide range of species. This is particularly true for ectotherms, which are animals that rely on environmental temperatures to regulate their body temperature. Ectotherm metabolic rates vary with thermal conditions, directly impacting activity levels, interactions with other species, and ecosystem services. In urban heat island environments, variation in temperature across both the short (e.g. days and seasons) and long term (e.g. years) is often more extreme than in natural settings due to heat retention by surfaces such as pavement, asphalt, and metal. Because of this, urban organisms may be under even greater pressure to adapt or acclimate to extreme temperatures.

Given that species may experience a broad range of temperature fluctuations across days, seasons, and years, the Roeder lab is investigating how behavioral, physiological, and genetic traits respond to increasingly hot and cold temperatures using ants as a study system. Relevant responses to thermal variability include minimizing exposure to stressful microclimates through behavioral avoidance of undesirable temperatures, acclimating physiologically to stressful temperatures when avoidance is impossible or disadvantageous to the colony (e.g. when foraging takes priority over individual safety), and regulating expression levels of genes associated with thermal resistance (e.g. heat-shock, thermal tolerance, and protein-folding regulatory genes).

As a part of a long-term investigation into how organisms respond to variable abiotic environments, the Roeder lab is conducting a two-year study (Summer 2025-Spring 2027) in Minnehaha County that aims to investigate the following questions using three ant species (Lasius neoniger, Tapinoma sessile, Tetramorium immigrans) in different subfamilies:

1. Do activity levels, heat tolerance, and preferred temperature correlate to local site temperatures and daily temperature variation? If so, this would signify adaptation or acclimation to urban warming and thermal variability in abiotic environments. We hypothesize that thermal tolerance and preferred temperatures measured under laboratory conditions will reflect activity patterns and temperatures at each sampling site for all species. Species with higher heat tolerance will also exhibit preference for warmer temperatures and greater activity during the warmer parts of the day and at warmer sites.

2.    Does exposure to short bouts of challenging hot and cold temperatures (such as an ant might experience when on a foraging trip or when defending a colony against threats) increase an individual’s ability to tolerate subsequent exposure to stressful conditions (called heat and cold hardening)? We hypothesize that when exposed to very hot conditions, species with higher initial heat tolerance will exhibit a heat hardening response but will be unable to maintain robust cold tolerance, while species with a lower initial heat tolerance will suffer decreases in both heat and cold tolerance following exposure. When exposed to very cold conditions, species with greater initial cold tolerance will have higher cold resistance in subsequent cold exposures but will be unable to maintain initial levels of heat tolerance, while species with low initial cold tolerance will increase their cold resistance upon subsequent exposure but maintain normal heat tolerance.

3.    After exposure to stressful thermal conditions, do ant species up- or down-regulate heat-shock gene expression in a similar manner? We hypothesize that genes associated with heat-shock response, heat tolerance, and protein folding in other ant species (candidates include hsf1, hsc70-4h, hsp83, hsp90, hsc70-5) will exhibit greater expression upregulation in ants with lower heat tolerance than in ants with higher initial heat tolerance due to constitutive upregulation of these genes.

Students involved in this project will learn skills in behavior, ecology, and molecular biology, providing cross- discipline training applicable to many fields. Students will have the opportunity to engage in field ecology, lab assays using living invertebrates, and molecular lab techniques from RNA extraction through RT-qPCR.