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. Ants may respond to thermal variability by 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). My lab is also interested in how these responses vary between ants native to South Dakota and non-native ant species.

The Roeder lab is currently conducting a 3-year study in Minnehaha County that aims to investigate the following questions using two abundant ant species in the western region of the state-the native Lasius neoniger and the non-native Tetramorium immigrans.

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 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)? The ability to acclimate may provide future protection against daily and seasonal changes in temperature. However, short bouts of exposure to very stressful conditions might be energetically costly and cause cellular damage. We hypothesize that when exposed to moderately hot conditions, species with higher heat tolerance will exhibit heat hardening. When ants are exposed to moderately cold conditions, species with greater initial cold tolerance will increase their cold resistance to subsequent cold exposures. Exposure to extremely stressful hot and cold conditions will result in decreased thermal tolerance for all species.

3.    After exposure to stressful thermal conditions, do native and non-native ant species regulate heat-shock gene expression in a similar manner? Ants with high heat tolerance may experience constitutively up-regulated heat-shock gene expression, while species living in less stressful conditions may facultatively up-regulate expression to address transient thermal challenges. We hypothesize that genes associated with heat-shock response, heat tolerance, and protein folding will exhibit greater changes in expression in ants with lower heat tolerance than in ants with higher heat tolerance due to the proposed 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.