drawing by Nadine Dupérré

Arachnids are one of the major groups of arthropods, and show a diversity of behaviors, lifestyles, and features that make them fascinating organisms to study. Arachnids are also one of the most species-rich groups of organisms, yet they have not been nearly as well-studied as some of their arthropod kin. We seek to determine the systematic relationships among the 11 orders of this ancient group of chelicerates by utilizing information from mitochondrial genomes. We are finding that some arachnid mitochondrial genomes have quite unusual features, and that they encode some of the smallest transfer RNA genes known. Learn more about these charismatic creatures and this NSF-funded project by clicking on the ricinuleid illustration to the left.

Evolution of mitochondrial transfer and ribosomal RNAs

We have discovered that the transfer RNA genes in the mitochondrial genomes of many arachnids are truncated and are missing the sequences for one of the arms typically encoded by tRNA genes. Many of the 22 mitochondrial tRNA genes have sequences that are unable to form the cloverleaf-shaped secondary structures found in typical tRNAs of nearly every other organism on the planet. Spider tRNA genes are even more unusual, in that they also often lack the sequence for the 3' aminoacyl acceptor stem. How such unusual tRNAs can function is unknown. We seek to understand when in evolutionary history these aberrant tRNAs arose within arachnids, and whether the mitochondrially encoded ribosomes have also undergone reductions in size due to loss of helices.

My lab has discovered that spiders emit fluorescence in response to ultraviolet light. Very few organisms are known to fluoresce, so we surveyed diverse spider families for this novel character. Our data suggests that the expression of fluorescence is under selection. Our work on the phylogenetic distribution of fluorescence will inform further research on its evolution and on the potential behavioral and ecological roles fluorescence may play in visual signaling among spiders, insects, and birds. For instance, we seek to determine whether fluorescence helps make spiders cryptic from or conspicuous to their predators and prey. I also am collaborating with chemist Scott Reed to isolate and identify the chemical compounds (fluorophores) responsible for spiders’ fluorescence. It is possible that novel compounds are involved that may potentially have medical or other practical applications.

My early research focused on population-level study of factors that influence speciation and the distribution of organisms (in both spiders and amphibians), and I continue to be interested in these questions. With Wayne Maddison, I studied the phenotypic changes and neutral genetic changes in mitochondrial loci that accompanied isolation of jumping spiders on the islands of montane habitat in the southwestern U.S. known as "sky islands". We found evidence that sexual selection has driven phenotypic diversification in the jumping spider Habronattus pugillis. Currently I am surveying variation in the jumping spider Habronattus oregonensis, which inhabits varied montane habitats of the western U.S. My lab seeks to determine whether selection drives geographic color variation in males, and if so, whether it is natural selection or sexual selection via female choice. By studying variation in male color, courtship behavior, habitat, and molecular markers, we seek to explore tradeoffs between crypsis and conspicuousness, and to examine the potential interplay between sexual and natural selection from one geographic region to another.