Free Radical Stress

Free radicals are highly reactive species of molecules that cause immense damage to other molecules that contain double bonds. Most of us are familiar with household bleach or hydrogen peroxide. Both can be used to remove colors, commonly referred to as bleaching. This works because the free radical chlorine in bleach and the free radical peroxide in hydrogen peroxide attack the double bonds. In fact, double bonds in organic molecules are responsible for their unique colors and odors. Hence, a peroxide-based air freshener will also remove odors! However, in an organism's body free radicals do much more harm than simply removing color. When these compounds attack a cell membrane, they punch holes in the phospholipid bilayer leading to loss of the membrane's integrity. Fortunately, when at lower levels, the body can counter free radical attack by releasing antioxidants. These enzymes harvest or neutralize free radicals, preventing them from causing harm to the boy. These enzymes are parts of ancient pathways originally evolved in response to the rapid explosion of photosynthetic organisms that release oxygen into the environment. Oxygen, when assaulted by UV light readily creates free radical oxygen. This causes many health problems and also protects the earth. Antioxidant enzymes such as superoxide dismutase, glutothione reductase, glutothione transferase, catalase, and general peroxidase are among but a few that scavenge free radicals. I was actively trying to develop a proactive monitoring strategy using antioxidant enzymes to monitor stress. However, we have since replaced this physiological approach with a genomic one.


Jones, L., D.R. Gossett, M.L. McCallum, and S.W. Banks. 2010. The antioxidant defense system in tadpoles of the American Bullfrog (Rana catesbeiana) exposed to Paraquat. Journal of Herpetology 44(2):222-228.

Environmental Estrogens

Endocrinally active compounds like environmental estrogens are a important problems for environmental health. Reduced human sperm counts, osteoporosis, immunosuppression, depression and a host of other human ailments have been directly or indirectly tied to exposure to these compounds. Although there are many sources of environmental estrogens, one important source is herbicides used in agronomic settings. Many of these are capable of mimicking estrogen when they enter the body. As such, they trigger an array of metabolic chain responses that can lead to uncountable physiological disturbances. The hypothalamic-pituitary-gonadal axis is one of these. Many studies have demonstrated interactions between potential and actual environmental estrogens and reproduction. Most research has focused on the physiology and anatomies such as reduced fecundity, infertility, and related calcium metabolism. However, behavior is also a vital component of reproductive biology. As a doctoral student I first envisioned testing if environmental estrogen exposure could interact with the sexual selection process. However, after graduation I did not have that resources to do this kind of work with frogs as I envisioned it. So, I broke the project into a series of smaller subcomponents, each handled by a different undergraduate or team of undergraduates. We shifted the organism to a widely available insect (the mealworm) and ran the experiment with them. The problem was that the role estrogen plays in insect physiology is largely unknown, making this approach even more interesting. Our results provided convincing evidence that sexual selection processes were circumvented by environmental estrogen exposure. It also provided evidence that estrogen plays a bigger role in insect physiology than was previously believed.

McCallum, M.L., M. Matlock, J. Treas, B. Safi, W. Sanson, J.L. McCallum. (2013). Endocrine disruption of sexual selection by an estrogenic herbicide in Tenebrio molitor. Ecotoxicology 22:1461-1466. (Altmetrics ranked it #3 among articles of similar age in the journal Ecotoxicology as of 2018.


I have been collaborating with Dr. Yonathan Tilahun on this project. We have teamed his background in genomics with mine in ecotoxicology to develop a novel use of genomic tools to evaluate ecotoxicological outcomes. At this time, we have presented preliminary data at scientific meetings, and one student won a presentation award for some of this work. In the process, we are also constructing draft genomes for the commercially relevant freshwater prawn, Macrobrachium roosenbergi and a small frog, Acris blanchardi. We also intend to apply the work to catfish, which already have available genomes. The draft genomes are necessary in order to evaluate mRNA used in the genomic analysis with Partek Flow. The outcomes from this research promise to raise signficant attention in both the aquaculture and conservation communities. We are currently analyzing data and writing manuscripts associated with this research. We are also anxious to see how these data influence currently accepted phylogenies in the systematic literature.

Research in progress as of June 2021:
McCallum ML, Tilahun Y. Draft Genome of Blanchard’s Cricket Frog, Acris blanchardi. In Prep.

McCallum ML, Tilahun Y. Draft Genome of the Giant Freshwater Prawn. In Prep

McCallum ML, et al. Genomic approaches using Environmental RNA for stress detection in aquatic organisms and ecosystems. (working title).