Herbivorous insects and their hostplants together comprise about half of all terrestrial eukaryotes (Futuyma and Agrawal 2009) and are food for most of the rest. Among beetles alone there are over 135,000 described herbivores (Farrell 1998). With plant feeding insects exceeding 400,000 described species and estimates of double that number on Earth (Mitter et al. 1991) this is the most species rich class of interactions known. Understanding the plant-insect interface is therefore important if we are to understand the role of ecological interactions in generating diversity. My long-term plan is to investigate the mechanisms behind the diversification of the genus Monochamus, a group of economically important, world spanning, longhorned beetles that attack a wide array of seed plants. My PhD project focuses on the ecologically divergent clade comprising the Holarctic conifer feeding species, ecologically and economically important in coniferous forests. This system provides the perfect setting for exploring a number of questions pertinent to diversity: the origin of major natural history shifts, speciation, plant-insect relationships, ecological release and chemical mediated communication. My thesis will try to address each point as it relates to this system.
By sampling all conifer feeding Monochamus species worldwide, and closely related genera, I hope to determine the origin(s) of conifer feeding in the genus. By sequencing genes from the beetles I can build a branching diagram of how the beetles are related to one another and what their ancestors were likely eating. This will tell us if the group had a shift from feeding on other plants to conifers and if that shift helped them to escape ‘arms races’ with plant defenses. Current evidence supports the shift hypothesis but is missing many species, including all from North America.
To look at how host-plants may have influenced species formation I focus in on the species Monochamus clamator in western North America. This species’ five subspecies span the continent north to south and from west Texas to the pacific coast. On mountaintops in the Great Basin these beetles are restricted with a single conifer species. I am sequencing the transcriptomes of these beetles to see how many species there are, if they have adapted to individual host tree species and if their genes for ‘smelling’ have evolved through isolation with the plants. These beetles have extremely long antennae with smell sensors, which they use to find trees to feed on and their same-species mates. I hypothesize that through adaptation to different plants, the beetles evolve independently of one another.
These beetles use their antennae like we use our eyes when seeking a mate. When scent molecules land on special receptors genes are turned on and signals are sent to the insect’s brain. Through transcriptome building I hope to identify the genes responsible for smelling host trees and potential mates. I will also be analyzing the chemicals attached to the backs of female beetles to see if they are unique to species or populations of M. clamator in the west. Changing these chemicals may be a first step in isolating subgroups of a species destined to become new species.
I am also working on other projects that include: the phylogeny and coevolution with plant defenses of the milkweed longhorn genus Tetraopes, new species descriptions of beetles, a beetle inventory of Gorongosa National Park in Mozambique and A survey of insects on the Navajo Reservation in the southwestern United States. I appreciate samples that may contribute to any of these projects and encourage you to contact me if you would like to help!
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