CAREER: Venom Evolution in Sicariid Spiders: A System for Undergraduate Training in Integrative Biology

Lewis And Clark College, Portland OR

Investigators

Abstract

Spider venoms are cocktails of chemicals evolutionarily designed for prey immobilization. Large differences in venom composition among the few studied species make the rest of the 39,000 species exciting sources of discovery of novel chemistry. Moreover, this chemical diversity makes a great context for studying evolutionary mechanisms that create novel toxins and modify them over time. This CAREER grant will fund development of an undergraduate-centered research program focused on the evolutionary origin and diversification of a unique and medically important toxin in venoms of brown recluse spiders and their relatives (Sicariidae). This toxin, sphingomyelinase D (SMase D) causes dermonecrotic lesions after bites of these spiders. The evolution of SMase D is particularly interesting because this enzyme is unique to venoms of sicariid spiders and pathogenic bacteria that cause disease in farm animals. Recent evidence from the PI and collaborators indicates that the evolutionary history of this toxin includes lateral transfer between spiders and bacteria. Furthermore, this toxin is a member of a gene family in spiders that undergoes periodic homogenization among different members, and either gene duplication and loss, or turning on and off of genes, which has resulted in loss of SMase D activity in some species. The specific research goals are to: (1) resolve relationships among worldwide representatives of species in this lineage and their close relatives using molecular phylogenetic analyses; (2) analyze the dynamics of origin and loss of venom-expressed SMase D using comparative enzyme assays and analyses of venom-expressed genes (cDNAs) from across the complete range of species with this toxin; (3) refine our understanding of the source of origin by probing for related genes in related groups of spiders. Understanding the mechanisms of origin and diversification of SMase D will serve as a case study of the molecular evolution of a unique toxin, and will provide information of medical relevance. Understanding the distribution and diversity of the SMase D molecule will inform us about the risks of bites from related species, and will aid in the development of treatments that are effective against bites of any member of this spider family. In so doing, it will promote awareness of the value of understanding basic systematics, organismal diversity, and evolution for the field of biological toxicology. Educational goals: This work will involve undergraduates in collaborative, interdisciplinary research that spans organisms and molecules. They will learn the value of approaching questions with an evolutionary (historical) perspective. In coursework, the PI will: (1) expand a phylogenetic biology course at Lewis & Clark College that includes bioinformatics, reconstruction of tree topologies and ancestral character states, and applications of these methods; (2) create a non-majors arachnology course that emphasizes the value of evolutionary approaches and integrated knowledge of organisms; (3) create a Web-based interactive diagnostic key for Loxosceles and Sicarius species diversity that is connected to the Tree of Life Web site.