Posted: April 4, 2018

This is the 1st of ten short news articles written by students, during the professional development class. This year we had the students interview their advisor(s), in an effort to help them better understand the larger context of their projects.

From Cell to Smell--Investigating Chemical Defense Evolution
By Adam Rork

Whether it's a group of lady beetles, a stink bug, or an earwig, we've all smelled insects with unpleasant odors, usually in our homes where we don't want them. What makes these insects smell so bad when bothered, though? Generally, the odor that they give off is a chemical defense mechanism that has evolved to ward off predators. To Tanya Renner, Assistant Professor of Entomology at Penn State, these organisms represent complex and fascinating evolutionary networks of genes, enzymes, chemicals, and physical characteristics, all of which contribute to their chemical defenses. One of the primary interests of her lab's research is understanding the evolution of chemical defense in ground beetles, specifically bombardier beetles.

Why bombardier beetles? It isn't simply that they are a charismatic beetle with an interesting name. Tanya and her lab are interested in understanding how certain genes that play roles in general insect metabolism have evolved over time for defensive purposes in insects - such as spraying caustic chemicals from the abdomen at temperatures up to 212°F!

That seems like a lot of moving parts to understand at once; how is such a system studied? "The biggest thing is that we are using genetic-based methods to solve our problems", says Tanya. Looking into the summation of an organism's genes, enzymes, chemistry, and coupling that information to physical characteristics, allows researchers to piece together intricate puzzles regarding the evolution of such traits.

To detect mechanisms which give rise to different defensive strategies, it is necessary to conduct studies across the entire ground beetle family. Members of Tanya's lab are also interested in a group of ground beetles closely related to the bombardiers which mostly produce formic acid. Using molecular approaches, they can examine which metabolic processes may be upregulated in defensive glands versus the rest of the body. Once they identify a metabolic pathway that is highly expressed in defensive glands, they can infer the function of those genes and conduct experiments to determine if they play roles in the biosynthesis of target chemicals.

Researchers in the lab's larger team of collaborators use methods to shut off genes within the insects' defensive glands, which allows one to study how gene silencing affects the final chemical output. Once the metabolic pathways contributing to the production of defensive chemicals have been elucidated in enough taxa, comparative investigations can be made at the genetic level. By doing so, scientists can begin to understand the evolutionary differences among species, which can influence gene expression, biochemical pathways and defensive strategies.

Odorous insects are all around us. The next time that you find a stink bug or lady beetle in your home, take a moment to appreciate its smelly defensive abilities before you return it to the outdoors.