Collaborative Research: The genetic basis, biosynthetic pathways and evolution of chemical defense in carabid beetles

The main goal of this project is to understand, at the molecular level, one of the most remarkable chemical defense systems found in nature - the explosive, extremely hot spray of the bombardier beetles. Insects make up much of the animal life that has evolved on Earth. Understanding why there are so many different kinds of insects and why they are so successful is fundamental to understanding how the wide diversity of life evolved. Insects are well known for producing many different chemical compounds that are required for their communication. Some chemicals help them to locate mates and food resources, others help them to organize activities within the nest or hive, and many others are used to warn off and defend against predators. This project focuses on this last aspect and is specifically testing the idea that the genes responsible for production of the hot chemical spray of the bombardier beetles are closely related to the genes responsible for producing similar chemicals in the insect's outer shell or exoskeleton. A main strength of the project is that it tackles this question by using multiple complementary approaches and by comparing eight different beetle species that are related to varying degrees. Half of these species have evolved a chemical defense system, the other half have not evolved this ability. Many college students and young scientists will receive scientific training in conjunction with the project. People of all ages are highly captivated by these beetles, particularly school age children. With the bombardier beetle as a model, the project will help develop elementary school level hands-on activities and lesson plans on topics in chemical ecology and biological chemical defense evolution that will reinforce the Next Generation Science.

Ground beetles and their relatives form the largest clade of organisms that use a single homologous gland system to produce no less than 19 distinct classes of chemical compounds for defense. This project will develop a detailed functional and evolutionary understanding of defensive chemistry evolution by focusing on species from the four lineages of quinone producing carabid beetles, including species commonly known as the bombardier beetles, which chemically blast their defensive quinones at extremely hot temperatures (up to 100 °C). Using a multidisciplinary approach, this project will identify genes involved in quinone production, elucidate chemical biosynthetic pathways, and describe the genetic architecture of quinone evolution. From gland-specific transcripts, candidate genes related to the production of defensive secretions will be identified and gene function will be validated experimentally by blocking gene transcription and looking at phenotypic changes in the compounds produced. The researchers will test the hypothesis that the genes up-regulated in secretory cells during quinone synthesis are closely related to those involved in quinone production in arthropod cuticle. Thus the project will empirically address the well-known, but untested, scenario of how the bombardier beetle evolved its explosive defense abilities. Ultimately, this project will explore how genetics and chemistry can interact over time and will reveal insights into the fundamental process of evolution.