Evolution of Biotic Interactions

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News
If you click on the title, you can read reporter Carolyn Wilke's story in the New York Times "Trilobites" features about the evolution of the plant-penetrating ovipositor (egg-guide) of Scaptomyza flava: "While Other Insects Played, This Species Evolved the Blade." 

Scaptomzya is a genus that evolved deep within the Drosophila lineage (and is the sister lineage to the Hawaiian Drosophila). The story features research led by Dr. Julianne Peláez and Dr. Andrew Gloss (that scientific study is here) while Ph.D. students in the lab.

See the videos of females making feeding and oviposition punctures in the genetic model plant Arabidiopsis thaliana leaves below. In the first video Julianne made you can watch the female turn around and drink the juice that seeps it the wound she's made. In the second video you can see what it looks like from the other side of the leaf as the female's two jaw-like ovipositor valves scoop out the hole (but, cleverly, she keeps the leaf's epidermis intact to protect the egg, we think, from drying out)--it looks like a mouth, but isn't! It is her ovipositor, the organ insects use to lay eggs. We've been studying interactions between this insect and its host plants as model for understanding the evolution and molecular mechanisms underlying plant-herbivore interactions.

Welcome
​The Whiteman Laboratory is at the University of California, Berkeley is within the Department of Integrative Biology and the Genetics, Genomics, & Development Division of the Department of Molecular & Cell Biology. We are also affiliated with the Helen Wills Neuroscience Institute, the Graduate Group in Microbiology, the Center for Computational Biology, the Essig Museum of Entomology, the Museum of Vertebrate Zoology and the University and Jepson Herbaria. 

Our research follows from Charles Darwin and Alfred Russell Wallace, who focused on the evolution of new traits shaped by ecological interactions between organisms, whether within or between species. These biotic interactions are an evolutionary crucible in which new adaptations are forged--traits that increase the fitness of their bearers. Adaptations arising from competition, host-parasite, predator-prey and mutualistic interactions are more straightforward to study than those shaped by the abiotic environment because their genomic architectures tend to be simpler and their evolutionary histories more dynamic. Species interactions can also drive the evolution of reproductive isolation, resulting in the origin of new species.

We use interdisciplinary approaches to study the role that species interactions play in driving the evolution of new adaptations and new species. We address these questions by integrating across as many levels of biological organization as possible, but with the goal of dissecting the genetic and molecular mechanisms, using tools from behavior, biochemistry, chemical ecology, comparative anatomy/morphology/physiology, computational biology, evolution of development, genetics (including CRISPR-Cas9 genome editing), genomics, molecular and cellular biology, plant biology, phylogenetics, and neuroscience. The reason so many different approaches are needed is that we study traits in multiple, interacting species, especially those involving host-parasite, plant-animal and plant-animal-microbial interactions. One of our main models is a leaf-mining drosophilid fly closely related to Drosophila melanogaster called Scaptomyza flava that attacks Arabidopsis thaliana. This duo allows us access to functional genomics and genetics on both sides of the plant-herbivore equation (Trudy Mackay referred to this once as "my model organism eats your model organism"). We also use D. melanogaster and other Drosophila species as study organisms in their own right.

An emerging theme in our lab focuses on the evolution of toxins produced by bacteria, plants and animals, as well as the evolution of toxin resistance. Sometimes these toxins, or even the genes involved in making them, are acquired by a different species through the diet or horizontal gene transfer. 

One of the most salient examples of how toxins can drive adaptation in other species is the monarch butterfly (images below by Julie Johnson). Eggs hatch on toxic milkweeds and as the caterpillars eat, they sequester cardiac glycoside heart poisons in their bodies through metamorphosis and are nearly completely resistant to their negative effects. The ability to resist and even acquire the toxins as a defense of their own opened a door to a suite of adaptations in the monarch, from its bright colors, which evolved to warn birds of their toxicity, to their migration from the prairies of Canada and the U.S. to the mountains of Mexico. These abilities have reverberated up to higher trophic levels as well. Recently, we and collaborators discovered that the black-headed grosbeak that preys upon these butterflies and is resistant to their toxins evolved convergent evolutionary changes in the target of the poisons, the sodium pump.

Finally, we also have a collaborative project on Broad-tailed hummingbirds that seeks to understand the evolution and genetic basis of foraging traits, including bill morphology, migratory behavior, and color vision. All of these projects are at the interface between species, even if the systems are diverse. 

Why do we study biotic interactions?